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Pharmaceutical Analysis:- PDF

Description

Best And Easy Notes

 

 

SENGHUNDHAR COLLEGE OF PHARMACY
TIRUCHENGODE

 

 

 

 

 

Estd. 2017

PHARMACEUTICAL ANALYSIS-I
B.PHARM- I YEAR
I SEMESTER

PREPARED BY:
Mrs.N.Gayathri..M.PHARM.,
(SUBJECT INCHARGE)

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PHARMACEUTICAL ANALYSIS SYLLABUS

UNIT-I

(a) Pharmaceutical analysis- Definition and scope

1) Different techniques of analysis

11) Methods of expressing concentration

iii) Primary and secondary standards.

iv) Preparation and standardization of various molar and normal solutions-

Oxalic acid, sodium hydroxide, hydrochloric acid, sodium thiosulphate, sulphuric
acid, potassium permanganate and ceric ammonium sulphate

(b) Errors: Sources of errors, types of errors, methods of minimizing errors,
accuracy, precision and significant figures

(c) Pharmacopoeia, Sources of impurities in medicinal agents, limit tests.

UNIT-I

Acid base titration: Theories of acid base indicators, classification of acid base
titrations and theory involved in titrations of strong, weak, and very weak acids
and bases, neutralization curves

Non aqueous titration: Solvents, acidimetry and alkalimetry titration and
estimation of Sodium benzoate and Ephedrine HCl

UNIT-II

Precipitation titrations: Mohr’s method, Volhard’s, Modified Volhard’s, Fajans
method, estimation of sodium chloride.

Complexometric titration: Classification, metal ion indicators, maskingand
demasking reagents, estimation of Magnesium sulphate, and calcium gluconate.

Gravimetry: Principle and steps involved in gravimetric analysis. Purity of the
precipitate: co-precipitation and post precipitation, Estimation of barium sulphate.

Diazotisation titration: Basic Principles,methods and application of diazotisation
titration.

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PHARMACEUTICAL ANALYSIS SYLLABUS

UNIT-IV

Redox titrations
(a) Concepts of oxidation and reduction
(b) Types of redox titrations (Principles and applications)

Cerimetry, Iodimetry, Iodometry, Bromatometry, Dichrometry, Titration
with potassium iodate

UNIT-V
Electrochemical methods of analysis

Conductometry- Introduction, Conductivity cell, Conductometric
titrations, applications.

Potentiometry - Electrochemical cell, construction and working
of reference (Standard hydrogen, silver chloride electrode and
calomel electrode) and indicator electrodes (metal electrodes and
glass electrode), methods to determine end point of potentiometric
titration and applications.

Polarography - Principle, IIkovic equation, construction and

working of dropping mercury electrode and rotating platinum
electrode, applications

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PHARMACEUTICAL ANALYSIS UNIT-I

Definition

Â¥ Pharmaceutical analysis is a branch of practical chemistry or Quantitative Pharmaceutical
chemistry.

Â¥ Pharmaceutical analysis may be defined as application of analytical procedures used to
determine the purity,safety,quality of drugs & chemicals.

TYPES
There are two types of chemical analysis.

1. Qualitative (identification)
2. Quantitative (estimation)

1.Qualitative analysis :

>» Completely unknown sample is taken & analysed to presence or absence particular
substance.

» Various qualitative tests are detection of evolved gas, formation of precipitates, limit
tests, cooler change reactions, melting point and boiling point test etc.

2. Quantitative analysis :

>» Analytical techniques are mainly used to quantify any compound or substance in the
sample.

» These techniques are based in (a) the quantitative performance of suitable chemical
reaction and either measuring the amount of reagent added to complete the reaction or
measuring the amount of reaction product obtained, (b) the characteristic movement of a
substance through a defined medium under controlled conditions, (c) electrical
measurement, (d) measurement of some spectroscopic properties of the compound.

>» Examination of raw material

» Analysis of various drug sample

» Qualitative / Qunatitative analysis of sample.

» Diagnosis of various disease by using chemical analysis.

» Determination of radioactive compounds.

>» Determination of naturally occurring phytoconstituents (chemical compound )
>» Determination of different sample of water.

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PHARMACEUTICAL ANALYSIS  UNIT-I

INSTRUMENTAL METHOD

 

Vv

 

Vv

 

 

\

( OPTICAL METHOD OF

ANALYSIS(OR)

SPECTRAL ANALYSIS

ELECTRICAL
METHOD OF
ANALYSIS

 

 

 

 

SAK

Visible
spectrophotomet
ry(colorimetry)
Ultra-visible
spectrophotomet
ry

Infra red
spectrophotomet
ry

Atomic
absorption
spectroscopy
Nephlometry&
Turbidimetry
Refractometry

 

Vv

 

   
 

EMISSION
METHODS

 

 

 

1.Potentiometry
2.Conductometry
3.Voltametry
4.coulometry

5.Polarography

 

 

 

 

1.Emission

CHROMATOGRAPHY
TECHNIQUE

  

  

OTHER
TECHNIQUES

 

  

 

 

 

spectroscopy 4
2.Fluorimetry

3.Flame
photometry

 

 

 

 

 

COLUMN [ PLANNER

 

1.X-ray
spectroscopy

2.mass spectroscopy

 

 

 

1.UPLC(ultra performance liquid chromatography
2.GC(gas chromatography )3.HPLC

4.Size Exclusion 5.lon Exchange 6.Affinity
chromatography
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N

l.paper chromatography

2.TLC(Thin layer chromatography)

3.HPTLC(High performance thin
layer chromatography.

 

 
PHARMACEUTICAL ANALYSIS

UNIT- I

NON-INSTRUMENTAL METHOD

 

Vv

| Gravimetric Analysis |

v

 

1.Electrogravimetry

2.Thermogravimetry

 

N

 

Titrimetric (or)

Volumetric

 

analysiss

[ Gasometric analysis

Volume of gas absorbed

 

y

y
| Proximate assay |

Determination of the
amount of organic
constituent.

(or)evolved is estimated

Eg:CO2,O2,nitrogen,

cyclopropane

 

 

  
  
 
 
 
     
    

Chemical
Method

Biological
Method

1.Invitro method

 

 

Various chemical

2.Animal studies
test.

3.Microbiological

assay

 

ACID BASE

(Neutralisation
titration)

1,Acidimetry
2.Alkalimetry

3.Non aqueous acid
base titration

 

OXIDATION-
REDUCTON(REDOX
TITRTION)

Iodimetry,lodometry

Titanometry,Ceriometry

Potassium bromated
titration,pot.Iodate titration

Permanganometry

 

 

 

N

 

 

PRECIPITATION
TITRATION

1.Mohrs method
2.Volhards method

3.Fajans method

mixeducatiomé

TITRATION

COMPLEXOMETRIC

 

Misscellaneous
Method

1.Diazotisation

2.kjeldahl Method

3.Oxygen flask
combustion

4.Karl-Fischers titration

 
 

 

PHARMACEUTICAL ANALYSIS UNIT-I

METHODS OF EXPRESSING CONCENTRATION :
Concentration of solution is the amount of solute dissolved in a known amount of the solvent or solution.
Concentration = Amount of solute / Amount of solvent
The three different ways to represent the concentration of solution are:
1) Percent concentration
2) Chemical methods of expressing concentration

3) Solubility Expression

SOLUBILITY EXPRESSION:
1 gram of substance in

+ Very soluble: less than 1 ml of solvent or solution.

«+ Freely soluble: 1-10 ml of solvent or solution

“+ Soluble : 10 — 30 ml of solvent or solution

%° Sparingly Soluble: 30-100 ml of solvent or solution

% Slightly soluble: 100 -1000 ml of solvent or solution

“* Very slightly soluble : 1000 — 10,000 ml of solvent or solution

«+ Practically Soluble (or) insoluble : greater than 10,000 ml of solvent or solution

Percent concentration:

Percentage: It refers to the amount of the solute per 100 parts of the solution. It can also be called as
parts per hundred (pph). It can be expressed by any of following four methods,

(i) percent w/w (% w/w) percentage weight in weight
_ Wt. of solute x 100
% whw Wt. of solution

Example: 100%(w/w)Nacl solution is made by weighing 100g Nacl & dissolving in 100g of solution

(ii) Percent w/v (%ow/v) Weight to volume percent

Wt.of solute

% wily . Volume of solution .

Example: 4% (w/v) Nacl solution is 4g of Nacl in 100ml of solution

4

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PHARMACEUTICAL ANALYSIS UNIT-I

(iii) Percent v/v (% v/v) Volume to volume percent

_ ¥ol. of solute x 100
% viv Yol. of solution

Example: 10% (v/v) Nacl solution is 10ml of Nacl in 100 ml of solution

(iv) Percent v/w (%v/w) Volume to weight percent

Vol. of solute

* Wt. of solution 100

% viw

Example: 10% (v/w) Nacl solution is 10 ml of Nacl in 100g of solution

WAYS OF EXPRESSING CONCENTRATIONS OF SOLUTIONS IN CHEMICAL UNITS:

Concentrations of solutions in chemical units can be expressed in various ways including

Molarity (M )
Molality (m_ )
Normality (N )
Formality ( F ).
Saturated solution

VV VV WV

1.Molarity (M).

> The molarity of a solution is the number of moles of the solute dissolved in one litre (1000
ml) of the solution

> 1gm in 1000ml =1 mol

» Molarity is indicated by M

. . number ofmoles ofsolute
Molarity of a solution = — -
number ofliters of solution

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PHARMACEUTICAL ANALYSIS UNIT-I

2. Molality (m) .

» The molality of a solution contain the number of moles of the solute per kilogram of solvent
» Molality is indicated by m

number ofmoles ofsolute

 

Molality of a solution — -
number ofkilograms of solvent

3. Formality (F). The formality of a solution is the number of gram-formula weights of the solute
contained in one liter of the solution. Formality is indicated by F .

* ' . : number of gram - formula weights of solute
Formality of a solution — -
number ofliters of solution

4. Normality (N). The normality of a solution is the number of gram-equivalent weights of the solute
(Substance)contained in one liter(1000 ml ) of the solution. Normality is indicated by N

. number of gram - equivalent weights of solute
Normality of a solution

number ofliters of solution

number of milligram - equivalents of solute

number ofmilliliters of solution

Where a milligram-equivalent is 1/1000 of a gram-equivalent weight.
5.Saturated solution:

A saturated solution is a chemical solution containing the maximum concentration of a solute dissolved in
the solvent. Additional solute will not dissolve in a saturated solution.

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PHARMACEUTICAL ANALYSIS UNIT-I

PRIMARY STANDARD AND SECONDARY STANDARD SOLUTION.

> A primary standard is a reagent that is extremely pure (99.95-100.05%),
> Stable

>» has no waters of hydration, and

>» has a high molecular weight.

>» Inchemistry, a primary standard is a reliable, readily qualified substance.

ideal requirments of primary standard :

= It should be easily obtained,purified,dried,& preserved in pure form.
= It should not change due to effect of air during weighing.

= It should be non-hygroscopic

= It should have high relative molecular mass

= It should rapidly soluble

= Free from impurities.0.01%-0.025

Some features of a primary standard are;

. High purity ,Non toxic, cheap, readily available.
° Less rective & stable

. Low hygroscopicity and efflorescence

. High solubility (Gf used in titration)

. High equivalent weight

EXAMPLES OF PRIMARY STANDARD :

~* Potassium hydrogen phthalate
“ Arsenic trioxide,

¢ Sodium Oxalate

“ Potassium dichromate,

“+ Potassium bromate,

%* Potassium iodate

“ Benzoic acid

“* Granulated Zinc,

¢ Calcium carbonate

“+ Magnesium sulphate

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PHARMACEUTICAL ANALYSIS UNIT-I

SECONDARY STANDARD:

> Secondary standards are substance used for standardisations and their content of the active
substance has been found by comparing against a primary standard.
» Asecondary standard is a chemical or reagent which has certain properties such as

(a) It has less purity than primary standard
(b) Less stable and more reactive than primary standard
(c) But its solution remains stable for a long time

(d) Titrated against primary standard anhydrous sodium hydroxide (NaOH).

It is extremely hygroscopic.

It is used for quantitative analysis

Secondary standard solution is used to determine the concentration of analysis.

Secondary standard solution which for one or more of reasons cannot used as primary standard.
For example sodium hydroxide cannot be used as primarys tandard.

VVVVV

REASON:

It absorb water and carbondioxide from atmosphere and the composition of its solution is subject to wide
varations at different periods.

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PHARMACEUTICAL ANALYSIS UNIT I

PREPARATION AND STANDARDIZATION
PREPARATION AND STANDARDIZATION OF 0.1M SODIUM HYDROXIDE

PRINCIPLE AND REACTION :

Potassium hydrogen phthalate is titrated directly with sodium hydroxide and gives
potassium sodium phthalate by using Phenolphthalein as an indicator.End point is
Colourless to faint pink.

COOH COoOMa
+ MaQH + HO
COOK COOK
Potassium hydrogen sodium hydroxide sodium potassium Water
phthalate hydrogen phthalate

PREPARATION OF 0.1M NaOH :

Take 100ml of distilled water in a cleaned and dried 1000m1 volumetric flask.

Add 4.0g of NaOH with continues stirring

Add 700ml of distilled water and mix well

 

Make up the volume 1000 ml “ water. Mix the solution thoroughly

Keep the solution for atleast an hour and then carry out standardization

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PHARMACEUTICAL ANALYSIS UNIT I

STANDARDIZATION OF SODIUM HYDROXIDE

Weigh 0.5¢g of potassium hydrogen phthalate

(previously dried at 120° for 2 hours)

Dissolved in 75 ml of CO, free water

Add 2 drops of phenolphthalein and titrate with 0.1M NaOH solution

Appearance of permanent pink colour

 

Each 1 ml of 0.1M NaOH is equivalent to 0.020422 of Potassium hydrogen phthalate

4 Burette

| MORN

he. Tap

Conical Flask

phenolphthalein

 

 

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PHARMACEUTICAL ANALYSIS UNIT I

PREPARATION AND STANDARDIZATION OF
0.1M HYDROCHLORIC ACID SOLUTION

PRINCIPLE AND REACTION:

» It is based on the principle Acid base titration (Acidimetry).

>» HClis a strong acid & sodium carbonate is a weak base ,

» The end point can be detected by methyl red as indicator.

» First the sodium carbonate react with HCl forms sodium bicarbonate and
further titration with HCI will converts into sodium chloride.

i) Na,CO;3 + HCl ---> NaHCO; + NaCl

ii) NaHCO; + HCl ---> NaCl + H,0 + co,

PREPARATION OF 0.1M HCl:

Take 100ml of distilled water in a cleaned and dried 1000ml volumetric flask.

Add 8.5ml of HCl with continues stirring

Add 700ml of distilled water and mix well,allow to cool to room temperature

Make up the volume 1000 ml with distilled water.

Mix the solution thoroughly

 

Keep the solution for atleast an hour and then carry out standardization

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PHARMACEUTICAL ANALYSIS UNIT I

STANDARDIZATION OF 1M HCl:

Weigh about 1.5g of anhydrous sodium carbonate (previously heated at 270°c for Lhours)

Dissolve in 100 ml of water and add 0.1ml of methyl red solution.

Add the acid slowly from a burette with constant stirring.

Until the solution become faintly pink

Heat the solution to boiling , cool &continue the titration

 

Heat again to boiling and titrate further as necessary until the faint pink color is no longer affected
by continued boiling

Each Iml of 1M HCl is equivalent to 0.05299 of Na,CO;

Burette

Hydrochloric Acid

« Tap

Conical Flask

12

  

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PHARMACEUTICAL ANALYSIS UNIT I

PREPARATION AND STANDARDIZATION OF 0.1M SULPHURIC ACID
Principal and reaction :

» It is based on the principle Acid base titration (Acidimetry).
>» sodium carbonate is titrated directly with Sulphuric acid forms Sodium

sulphate.
> End point can be detected by using Methyl red (or) Methyl orange as an
indicator.
Na2CO3 + HeS04 —> Na2804 + HO + CO2
Sodium carbonate sulphuric acid sodium sulphate water carbondioxide

PREPARATION OF 0.1M H,S04:

Add slowly with stirring 5.4 ml of sulphuric acid in 800 ml of purified water

Make up to 1000m1 with purified water

Allow cooling at 25° C

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PHARMACEUTICAL ANALYSIS UNIT I

STANDARDIZATION OF 0.1M H,S0O,:

Weigh about 0.2g of anhydrous sodium carbonate (previously heated at 270°c for Lhours)

Dissolve in 100ml of water and add 0.1ml of methyl red solution.

Add the acid slowly from a burette with constant stirring.

Until the solution become faintly pink

Heat the solution to boiling , cool &continue the titration

 

Heat again to boiling and titrate further as necessary

until the faint pink coloris no longer affected by continued boiling

Each Iml of 0.1M H2SOy is equivalent to of 0.0098g of Na,xCO3

Burette

 

SULPHURIC ACID

 

 

 

« Tap

Conical Flask

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PHARMACEUTICAL ANALYSIS UNIT I

PREPARATION AND STANDADIZATION OF SODIUM THIOSULPHATE

PRINCIPLE AND REACTION:

>» It standardized by redox titration involving iodometric methods.

>» Potassium Iodate is reacted with excess potassium iodide in acidic
condition,results in liberation of iodine.

» Liberated iodine is titrated directly with sodium thiosulphate.

>» End point can be detected with disappearance of permanent blue colour due
to conversion of iodine ino sodium iodide.

KIO; + SKI + 3H)SOQx, ----------- >3K,SO, + 31+ 3H,O
Potassium Potassium sulphuric Potassium Iodine Water
Iodate Iodide acid sulphate
lL + 2NaS,0;  _~—_----------- > NaS40¢ + 2Nal
Iodine sodium thiosulphate sodium tetrathionate sodium iodide

PREPARATION OF 0.1M SODIUM THIOSULPHATE:
Weigh accurately about 25g of sodium thiosulphate
Dissolve it in 200 ml of water freshly boiled & cooled water.
Shake the content for 2 minutes

|

Make up the volume upto 1000ml with water. Keep the solution for atleast one hour and carry out
standardization

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PHARMACEUTICAL ANALYSIS UNIT I

STANADARDIZATION OF 0.1M SODIUM THIOSULPHATE:

Weigh 0.15 g of potassium Iodate

Dissolve in 25ml of distilled water in a 500ml conical flask.

Add 2g of iodate free potassium iodide & add 5 ml of Sulphuric acid

Iodine evolved is titrated with the sodium thiosulphate until yellowish green colour appears.

y
Add 3ml of starch solution and continue the titration until the solution change from blue to coloueless

 

Each 1m] of 0.1M sodium thiosulphate is equivalent to 0.0214 g of Potassium iodate

Burette

 

SODIUM THIOSULPHATE

 

 

 

I \ Conical flask

 

/ ‘ Potassium Iodate solution + Potassium iodide +
Sulphuric acid + Starch indicator

 

i Endpoint - Blue to Colourless

 

 

 

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PHARMACEUTICAL ANALYSIS UNIT I

PREPARATION AND STANDARDIZATION OF 0.1 N POTASSIUM PERMANGANATE
PRINCIPLE AND REACTION:

The main principle is it standardized by redox titration involving permanganometry.
Potassium permanganate is used as a powerful oxidising agent in acid medium.

Potassium permanganate evolves nascent oxygen in acid which is responsible for oxidation.
Potassium permanganate is reacted with oxalic acid in presence of sulphuric acid to form
potassium sulphate with manganese sulphate and by carbonic acid.

>» Potassium permanganate act as self indicator, the end point is appearance of pink colour.

VVVWV

NOTE: KMn0O4 is standardized by titration against using primary standard such as sodium oxalate or

oxalic acid or by using secondary standard sodium thiosulphate.

Molecular equations
2KMn0O, + 3H,SO, » K,SO, + 2MnSO, + 3H,0 + 5/0]

COOH aa
| 2H,0 + (O] ———» 2CO,, + 3H,0] x5
COOH

 

COOH
2KMnO, + 2H,SO, +5 . 2H,0 ——> K,SO, + 2MnSO, + 18H,0 + 1000,
COOH

 

PREPARATION OF 0.1 N POTASSIUM PERMANGANATE:
Weigh accurately 3.2g of potassium permanganate dissolve in 1000 ml

of distilled water

Heat on a water bath for 1 hour.

Allow to stand for 2 days and filter through glass wool.
Standardize the solution in the following manner.

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PHARMACEUTICAL ANALYSIS UNIT I

STANDARDIZATION OF 0.1 N POTASSIUM PERMANGANATE:

20ml of prepared oxalic acid solution in a conical flask

Add 5 ml of sulphuric acid

Warm the mixture to about 70°C

Then fill the burette with potassium permanganate solution

 

End point is appearance of pink colour.

 

— >| KMn0, (Secondary standard)

 

 

 

 

 

Oxalic acid + sulphuric acid

\
\
ix
(Primary standard)

End point: pale
permanent

 

 

 

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PHARMACEUTICAL ANALYSIS UNIT I

PREPARATION AND STANDARDIZATION OF 0.1M CERRIC AMMONIUM SULPHATE
[Ce (NH4)4 (SO4)4 . 2 H2O]
PRINCIPLE AND REACTION:

» The main principle is it standardized by redox titration involving ceriometry.

» In this titration arsenic trioxide reacts with sodium hydroxide to give sodium arsenite

>» This sodium arsenite is oxidised to sodium arsenate in presence of sulphuric acid by
cerric ammonium sulphate.

The reaction is very slow at the ordinary temperature.

Hence it is necessary to add osmic acid is added as a catalyst using ferroin as a indicator.

VV Vv

The first sharp colour change to pink orange red to pale blue.

AS20,; + 6NaOH wees > NaAsO,

(Arsenic trioxide) Sodium hydroxide (Sodium arsenite)

2Ce (SO4)2 + NazASO3 + H,O ----> Ce 2(SO4)3 + Naz;ASO4 + H,SO,

Cerric sodium Cerrous sodium Sulphuric acid
Sulphate Arsenite sulphate arsenate
4[Ce* te - wn-n--e-ee--e >cCe* ]

PREPARATION OF 0.1M CERRIC AMMINIUM SULPHATE:

Dissolve 65g of ceric ammonium sulphate

Dissolve it in a mixture of 30 ml of sulphuric acid and 500m1 of water with gentle heat

|

Cool& filter the solution then make up to 1000m1 with water.

Standardize the solution in the following manner.

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PHARMACEUTICAL ANALYSIS UNIT I

STANDARDIZATION OF 0.1M CERRIC AMMONIUM SULPHATE:

Weigh 0.2 g of arsenic trioxide(previously dried at 105°C for 1 hour) transferred to a 500m1 conical flask.

Add 25ml of 8%w/v of sodium hydroxide solution, swirl to dissolve and add 100m1 water,

mix well.

Add 30m! of dil.sulphuric acid,0.15m1 of osmic acid solution, 0.1ml ferroin indicator solution.

Titrate withO.1M cerric ammonium sulphate solution until pink colour changed to very pale blue.

 

Each lm] of 0.1M ceric ammonium sulphate is equivalent to 0.004946 of arsenic trioxide.

 

Cerric ammonium sulphate

 

 

 

 

Arsenic trioxide + sodium hydroxide +dilute

 

 

Sulphuric acid + 0.15ml of osmic acid + ferroin Indicator

 

 

 

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PHARMACEUTICAL ANALYSIS UNIT I

PREPARATION AND STANDARDISATION OF 0.1N OXALIC ACID SOLUTION:

REACTION:
H.C204 + 2NaOH ~= ----------- > Na,C,04 + 2H,O
Oxalic acid sodium hydroxide Sodium oxalate Water

Accurately measure 6.3 g of oxalic acid is taken in a clean dry beaker

It is dissolved in about 200ml of distilled water

Finally make up the volume to one litre in a volumetric flask

The solution is mixed properly to form 0.1N Solution of oxalic acid which is
finally transferred to a reagent bottle and is labelled.

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PHARMACEUTICAL ANALYSIS UNIT I

STANDARDISATION:
Pipette 25ml of the 0.1M NaOH

Transfer it into a clean conical flask to it

Add 2-3 drops of Phenolphthalein indicator

 

Titrate with 0.1N Oxalic acid solution until colour change from purple to
colourless

Burette

 

 

 

OXALIC ACID

 

 

4 Tap

Conical Flask

 

SODIUM HYDROXIDE

 

 

 

phenoiphthale

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PHARMACEUTICAL ANALYSIS UNIT-I

ERRORS:

Sources of errors

Types of errors,

Methods of minimizing errors,
Accuracy,

Precision and

Significant figures

LLL K KK

Definition of errors:

» The difference between the Observed value Or calculated value and true value is
known as Error.

> If the error in an analysis is large, serious consequences may result as reliability,
reproducibility and accuracy are the basis of analytical chemistry.

SOURCES OF ERRORS :

1.Improper samplings :

Error may occur due to improper samplings.

2.Errors during sample preparation :

Error may occur during sample preparation.

3.Error by the analyst:

Analyst can do error during analysis,it is also known as manual error.
4.Error by the equipments :

Error occur due to improper function of the equipment.
5.calibration error:

Error may occur if proper calibration is not done.
6.Reporting Error :

Error occurs due wrong or improper data or observation.
7.Calculation Error:

Error occurs due to wrong calculation.

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PHARMACEUTICAL ANALYSIS UNIT-I

8.Error in method selection :

Error may occur due to wrong method selection.

9.Error during transport & storage :

Error may occur due to improper handling of materials during transport & storage.
10.Error due to Laboratory Environment :

Due to unsuitable laboratory environment.

TYPES OF ERRORS:

1) Determinate or systematic or constant error and

2) Indeterminate or random or accidental error

DETERMINATE OR SYSTEMATIC OR CONSTANT ERROR

> Known to be analyst
» Usually one sided & preplanning these errors can be Eliminated

EXAMPLES OF DETERMINATE ERROR :
1) Error in the calibration and the operation of measuring instruments.
11) Impurities in the reagents and drugs
ii) Biased personal errors.
-Reading the meniscus
-Pouring and mixing
-In weighing operation
-In matching colours

-In making calculation

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PHARMACEUTICAL ANALYSIS UNIT-I

Determinate Error can be classified into
1.Personal errors

2.Instrumental errors

3.Reagent errors

4.Additive/constant errors

5.Proportional error

6.Error in method

Operational and Personal errors:

» These are due to an individual analyst is responsible and are not connected with the method or
procedure they form part of the personal equation of an observer.

>» Examples are:

Mechanical loss of materials in various steps of analysis.

Underwashing or over washing of precipitates.

Ignition of precipitate at incorrect temperatures.

SAMAK

Some analyst is unable to judge color changes sharply in visual titrations, which may
result in slight overstepping of the end point.

x

Some other analyst — related errors are : Carelessness Transcription errors, i.e. copying
the wrong information into a lab notebook or onto a label.

Â¥ Proper training, experience, and attention to detail on the part of the analyst can correct
these types of errors.

Reagents and instrumentation:

 

> Contaminated or decomposed reagents can cause determinate errors.

» Prepared reagents may also be improperly labeled.

» Impurities in the reagents may interfere with the determination of the analyte, especially at the
ppm level or below.

>» Numerous errors involving instrumentation are possible, including Faulty construction of
balances, Incorrect instrument alignment, Incorrect wavelength settings, Use of uncalibrated or
improperly calibrated weights.

» These problems can be eliminated by a systematic procedure to check the instrument settings and
operation before use.

> Such procedures are called std. operating (SOPs) in the many labs.

> There should be a written SOP for each instrument and each analytical method used in the
laboratory.

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PHARMACEUTICAL ANALYSIS UNIT-I

Instrumental error:

>

Due to defect in the instrument or non calibrated instrument is uesd.

Example:use of defective pipettes.

Electrical line voltage fluctuations are a particular problem.

This is especially true for automated instruments running unattended overnight. Instruments are
often calibrated during the day, when electrical power is in high demand.

At night , when power demand is lower, completely changing the relationship between conc. Of
analyte and measured signal.

Additive /constant errors:

>

>

Sometimes error will be constant throughout the analysis irrespective of amount/volume of
sample.

Ex:10.1, 20.1, 30.1ml

0.1 ml of error irrespective of volume.

Proportional Error:

>
>

proportionally increment in the absolute error.
Ex:10.1,20.2,30.3ml.
Absolute error 0.1 ml, 0.2ml , 0.3ml.

Errors in method:

> Wrong method selection
>» Example if any synthesis takes 3hrs to complete by we have given only 2hrs,then final

product will be defective.

INDETERMINATE OR RANDOM OR ACCIDENTAL ERROR :

>
>
>

These are random errors & may be known or not known to the analyst.
This error is unpredictable and difficult to identify
Sources of random error are :
Â¥ Samples handled improperly
Â¥ Inefficient or inappropriate equipment(E.g : A balance of low resolution or low grade
glassware )
Incorrect parameters of the method are employed
Presence of bubbles in burettes
Less trained operators
Fluctuation in environmental conditions like temperature & humidity

SAK

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PHARMACEUTICAL ANALYSIS UNIT-I

MINIMIZATION OF ERRORS:

By the following ways errors can be minimized:

Calibration of apparatus and application of corrections
Running a blank determination

Running a control determination

Use of Independent method of analysis

Running of parallel determinations

Standard addition

Internal Standards

Amplification methods

LLL LKR

Isotopic Solutions

Calibration of apparatus and application of corrections:

 

> Calibration of instruments, apparatus and applying necessary corrections

» Instruments commonly used in lab, such as spectrophotometer, electrical balance etc must be
calibrated before use.

» Pipettes, burettes, volumetric flasks, thermometers must be calibrated.

» The response of most of the instruments changes with time because of wear corrosion or
mishandling, etc.

» The determinate personal errors may be eliminated by care, practice and self discipline

Running a blank determination:

> By using blank determination analyst can determinate impurities present in reagents &
solvents & ultimately errors can be reduced.

Example :

Normal determination:

Analyte A+Reagent B+Methanol

Blank determination :
Reagent B+Methanol (the sample being omitted)

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PHARMACEUTICAL ANALYSIS UNIT-I

Running a control determination:

 

> Standard substance(known conc/amount)is taken & analyzed.
> Compared with the normal determination.

Normal determination:
Analyte A+Reagent B+Methanol
Control determination :

Standard A+Reagent B+Methanol

Can be calculated by following expression:
(Result found for Standard/Result found for unknown)=(Weight of constituent in standard/X)
X=Weight of the constituent in the unknown.
Use of Independent method of analysis:
> Two methods are used & compared.
Example: Standardization of Hcl both

>» by precipitation titration- titration with solution of strong base, precipitate of AgCl is
weighed.
> by acid base titration- neutarlization of reactants.

Running of parallel determinations:

Â¥ Duplicate /triplicate determinaions reduces accidental or indeterminate errors
Standard addition:

» Standard substance of known amount is added in the sample/analyte solution.
» Recovery study of the standard is done.

Sample A+Reagent(s) —_—------------- > 10ug (after analysis)
Sample A+ Standard A+ Reagents(s)  ------------ > 15ug (afteranalysis)

(0g) (Gug)

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PHARMACEUTICAL ANALYSIS UNIT-I

Internal Standards:

» Suitable internal standard is selected & analysed in same experimental conditions.

» Absorption of peak size of the IS & the series of known conc.is plotted against the
conc. values.

» This should give a straight line.

>» Any unknown conc. Can be determined by adding same IS & finding the ratio obtained
falls on the conc.scale.

Spectroscopy

CALIBRATION METHOD & STANDARD
ADDITION METHOD TITRATIONS.

       
  
  

300 500
250 400
z 200 = 300
§ 150 S
= 100 £
50
oO Oo

“10 15 20 25 30 20 -10 0 10 2a 30

 

Amplification methods:

Â¥Y Determination in which a small amount of material is to be measured, it can be measured by the
small sample can be reacted in such a way that every molecule produces two or more molecules
of some other measurable material.

Isotopic Solutions:

Â¥ Radioactive isotope element is added with unknown sample.
Â¥ The radioactivity of the isolated element is measured and compared with that of the added
element.

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PHARMACEUTICAL ANALYSIS UNIT-I

ACCURACY:
» The difference between calculated value & accepted real value is known as
accuracy
» It refers to the closeness of a measured value to a standard or known value.
>» Eg: In lab, you obtain a weight measurements of 3.2kg for a given
substance, but the actual or known weight is 10kg.
» Then the measurement is not accurate. In this case, your measurement is
not close to the known value
PRECISION:

>» It is measureof reproducibility of data within a series of measurements of
the same quantity

» The results within series are closly with one another are said to be
precise.

» Precise results are not necessarily accurate.

>» Eg: If you weigh a given subsatance five times and get 3.2kg each time,
then your measurement is precise but inaccurate.

@ @
WA

Accuracy Vs Precision

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PHARMACEUTICAL ANALYSIS UNIT-I

SIGNIFICANT FIGURES:

v A figure of digit denotes any one of the ten numerals (0,1,2,3,4,5,6,7,8,9)

v A Digit alone or in combination serves to express a number.

Y AS ignificant figure is a digit having some practical meaning,that is a digit
,»which denotes the amount of the quantity in the place in which it stands.

Y For Example in 0.456 , 4.56 & 546 there are three significant figures in each
number.

Rules for significant figures:

Â¥ All non zero numbers are significant.

Â¥ Zero between non zero numbers are significant

Y Leading zerors are never significant

Â¥ Zerors on the end of a number are significant only if there is a decimal point.

SIGNIFICANT FIGURES & MAHEMATICAL OPERATIONS
1.Adding & subtraction

2.Multiplication & Division

3.Rounding

Identifying Significant Digits:

» The various rules to identify the significant digits in writing or interpreting
numbers are:
Non zero digits are significant.
Eg:12 show two significant digits that is 1 and 2

>

>

» Zeros between two non —zero digits are significant.

» Eg: 209 here the zero between the non zero digits is significant.
>

Leading zeros are insignificant and trailing zeros are significant.

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PHARMACEUTICAL ANALYSIS UNIT I
PHARMACOPOEIA

PHARMACOPOFIA:
Introduction, List, History, Individual monograph.

INTRODUCTION:

* Pharmacopoeia Derived from Greek word ‘Pharmakon’ means drug (Remedy and
poison) and ‘Poiea’ means to make.

* Tt is a legal and official book issued by recognized authorities usually appointed by
Government of each country.

* Tt comprises list of pharmaceutical substances, formulae along with their description and
standards.

LIST OF PHARMACOPEIAS:

a) Argentine b) Austrian c) Belgian d) Brazilian e) British f) Chinese
g) Egyptian h) European i) French 4) German k) Hungarian

1) Indian m) International n) Italian 0) Japanese p) Yugoslavian

q) Mexican r) Netherlands s) Nordic t) Polish u) Portuguese

v) Rumanian w) Russian x) Spanish y) Turkish  z) United state.
HISTORY:
Indian Pharmacopoeia:

» Indian Pharmacopoeia Commission (IPC) is an Autonomous Institution of the Ministry of
Health and Family Welfare, Govt. of India.

» IPC is created to set standards of drugs in the country.

>» Its basic function is to update regularly the standards of drugs commonly required for
treatment of diseases prevailing in this region.

» It publishes official documents for improving Quality of Medicines by way of adding
new and updating existing monographs in the form of Indian Pharmacopoeia (IP).

> It further promotes rational use of generic medicines by publishing National Formulary of
India.

> IP prescribes standards for identity, purity and strength of drugs essentially required from
health care perspective of human beings and animals.

» IPC also provides IP Reference Substances (IPRS) which act as a finger print for
identification of an article under test and its purity as prescribed in IP.

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Comments and
reponses displayed
on website/mailed

Further revision
needed

 

   
   
   
   

PHARMACEUTICAL ANALYSIS UNIT I
PHARMACOPOEIA

 

Indian pharm.

acopoeia commission (IPC)

 

 

+

 

Scientific Body approved item for the IP

 

 

y

 

IPC Scentific s

taff Liaisons & review items

 

 

 

y

 

Item displayed

mailed separately for public review

on the website &

 

 

v

 

 

Public comments recieved

 

 

!

 

 

Experts committees review
comments and respond to the
scientific staff Liaisions

 

 

 

IPC Scentific st

 

analvse comments

aff compile and

 

\

 

 

No Further revision needed

 

 

 

Proposal accepted and published

 

 

!

 

 

INDIAN PHARMACOPOEIA

 

 

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Feedback from
stakeholders

 

 
 

 

PHARMACEUTICAL ANALYSIS UNIT I
PHARMACOPOEIA

BRITISH PHARMACOPOEIA:

Â¥ First edition of BP was published in 1864. It consist of two sections Part I: - Materia
Medica & Part II: - Preparation & compounds.

Second edition of BP was published in 1867.

Fourth edition of BP was published in 1898.

Fifth edition of BP was published in 1914.

Eighth edition of BP was published in 1953.

In this edition titles of drugs & preparations were in English instead of Latin and metric
system. It has been published annually.

SLR K

xq

In BP 2007 monographs has been introduced for material specifically used in preparation
of Traditional Chinese medicines.

UNITED STATE PHARMACOPOEIA;:(US.P)

Â¥ USP is a Pharmacopoeia (Compendium of drug information) for the United States
published annually by the United States Pharmacopoeia Convention, a non profit
organization thatowns the trade mark and copyright.

Â¥ The USP is published in a combined volume with the National Formulary as the USP-
NF.

Â¥ Drugs subject to USP standards include both human drugs as well as animal drugs.
First edition of USP was published on 15thDecember 1820 in both Latin & English.

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PHARMACEUTICAL ANALYSIS UNIT -I

IMPURITIES

Impurities in pharmaceutical substances :

» Chemical purity means freedom from all foreign material.

>» Itis not possible to obtain an absolutely pure compound.

>» And even analytical pure samples contain minute trace of other
substances which are called as impurities.

>» Purification of chemicals is expensive and much costly.

>» Refined sugar contains more than 99.9% of sucrose, vacuum salt
made by purification of rock salt, contains more than 99.9% of
sodium chloride.

Disadvantages of Impurities :

1. Impurities which have a toxic effect and cause unpleasant reaction in the body
when present beyond certain limits.

E.g. Lead and Arsenic.

2. Impurities which, though otherwise harmless,are present in such proportions that
is not desirable.

E.g. presence of sodium bromide in the more expensive potassium bromide is not
likely to cause harm to the patient.

» However, potassium bromide should contain only potassium bromide and
not contain large amount of sodium bromide.

3. Impurities which lessen the keeping properties of the substance.

E.g. a small amount of moisture may cause many substances to be easy oxidized or
to undergo hydrolysis.

4. Impurities which render the substance incompatibility with other substances.

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PHARMACEUTICAL ANALYSIS UNIT -I

5. Impurities which cause technical difficulties in use of the substance.
e.g. presence of potassium iodate in a sample or potassium iodide.

» Such a sample will liberate iodine on being mixed with a mineral acid due to
the interaction of both the substances

6. Impurities which impart a different odor or color to the main substance and so
are desirable.

e.g. sodium salicylate is often discolored due to phenolic impurities.

» Sodium chloride becomes damp due to the presence of traces of deliquescent
magnesium salts.

SOURCE OF IMPURITIES :

1. Raw material used in manufacture :

>» A good example is the presence of tin, lead ,silver, copper, cobalt, and gold
in bismuth salts.

» These metals occur along with bismuth in bismuth ores.

> Rock salt contains small amounts of calciumsulfate and magnesium
chloride, so that sodium chloride prepared from this source will almost
certainly contain trace of calcium and magnesium compounds.

2. The Methods of Manufacture :

* Contaminating by reagents and solvents during manufacturing process.
i. Reagents employed in the process

11. Reagents added to remove the other impurities

1. Solvents

iv. The Reaction Vessels

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PHARMACEUTICAL ANALYSIS UNIT -I

i. Reagents employed in the process :

> lead as an impurity may results from the sulfuric acid used as
reagent, especially if it has prepared by the lead chamber process.

>» Soluble alkali may be an impurity in calcium carbonate if the
calcium carbonate is made by the reacting calcium chloride and

sodium carbonate and not properly washed.

ii. Reagents added to remove the other impurities :
>» Potassium bromide is liable to contain trace of barium which is
added in the course of the manufacturing process to remove the

excess sulfate.

ii. Solvents :

>» Water is the solvent easily available and cheap.
>» Itis used in manufacturing of inorganiccompounds.
» This can rise to a trace impurities such as sodium,calcium,

magnesium, carbonate, chloride and sulfate ions.
>» These difficulties do not arise in the use ofpurified or distilled or

demineralized water.

iv. The Reaction Vessels :
>» The vessels used in the manufacturing process are of metals like
copper, iron, aluminum, zinc, nickel and tin though these days

many of them are replaced with stainless steel.
>» The above metals are introduced as impurities due to the solvent

action of the raw materials.
>» Glass vessels may give rise to traces of alkali.

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PHARMACEUTICAL ANALYSIS UNIT -I

3. Atmospheric contamination :

>» Atmospheric contamination may take place through dust, Sulphur
dioxide, hydrogen Sulfide etc.

>» Carbon dioxide and water vapor are possible contaminants of
substances which are affected by their action.

4. Decomposition of products during storage :

» Many chemical substances undergo changes due to careless
storages.

>» Ferrous sulfate is slowly changed into ferric oxide by air and
moisture.

>» Solution of potassium hydroxide absorbs carbon dioxide on
exposure to air and exerts a solvent action on lead glass.

> Bismuth carbonate turns black on exposure to sunlight for long
time.

5. Deliberate Adulteration with usless materials :

>» This still a common occurrence in some parts of the country where
the drugs and cosmetic act has not yet been properly enforced.

>» Therefore one has to be vigilant and purchase drugs only from
reputed manufacturers.

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PHARMACEUTICAL ANALYSIS UNIT - I

Definition of limit test :

«Limit test is defined as quantitative test designed to identify and control small
quantities of impurity which is present in the compound.

¢Limit test is generally carried out to determine the inorganic impurities present in
the compound.

*In short, limit test is to identify the impurities present in the substance and
compared it with the standard

“¢ Limit test for Chlorides
“* Limit test for Sulphates
¢¢ Limit test for Iron

¢¢ Limit test for Arsenic
“¢ Limit test for Lead

LIMIT TEST FOR CHLORIDES
REQUIREMENTS: -
Chemical required: Silver nitrate, dilute nitric acid, sodium chloride etc.
Apparatus required: - Measuring cylinder, glass rod and Nessler’s cylinder.

Principle :

>» Limit test of chloride is based on the reaction of sodium chloride with silver
nitrate in the presence of dilute nitric acid to form silver chloride, which
appears as opalescence in the solution.

» Nitric acid is added to prevent precipitation of other acid radicals solution,

because in presence of nitric acid other precipitate are not produced and

only chlorides ions is precipitated.

dil. HNO3
Nacl + AGNO; (——————wwewnnenenee > AgCl + NaNo;

Sodium chloride Silver nitrate Silver chloride Sodium nitrate

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PHARMACEUTICAL ANALYSIS UNIT - I

PROCEDURE:

Simultaneously carry out the standard and test solution of preparation are

followed by utilizing approximately the same time period.

 

Sl

No TEST SOLUTION STANDARD SOLUTION

 

To specified amount of Place 1 ml of 0.05845% w/v

;, Sample add 10ml of distilled) NaCl and 10 ml of distilled water
’ lwater labelled as 'Test'. and labelled as
‘Standard’.

2. |Add 10 ml of dil. HNO, | Add 10ml of dil. HNO.

Diluted to 50 ml mark with| Diluted to 50 ml mark with

till
distilled water distilled

4. |Add Iml of AgNO; reagent | Add 1 ml of AgNO, reagent

 

 

 

 

 

Stir each solution with separate glass rods and allowed stand for 5
minutes. Compare the opalescence transversely against a dark back

ground to have a better contrast for comparison.

OBSERVATION :

>» The opalescence in the sample is less than the standard-It passes
the test,It is standard

» The opalescence in the sample is more than the standard-It fails
the test,It is Sub standard

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PHARMACEUTICAL ANALYSIS UNIT - I

LIMIT TEST FOR SULPHATE
REQUIREMENTS
Chemical required: Hydrochloric acid, Barium sulphate and Barium chloride
Principle :
» The principle involved in the limit test of sulphate is precipitation method and

comparison of test solution with standard solution containing a known amount of
sulphates.

 

>» The sulphates are precipitated as barium sulphate by the reacting them with barium
chloride in the presence of hydrochloric acid.
» The hydrochloric acid is used to prevent the reaction of other acid radicals with barium
chloride.
> In presence of HCI, only sulphates are precipitated.
> Due to the formation of precipitation, the solution appears turbid and the extent of
turbidity depends on the the amount of sulphates present.
HCl
2-
SOP + Bally -x-e---eeee-+- > BaS0, + 9 2CL-
Sulphate ion Barium chloride Barium sulphate Chloride ion
PROCEDURE:
SI TEST STANDARD
INo

 

Dissolve specified amount of |Placed 1 ml of 0.1089 % w/v Solution of
1. |sample in 10ml of distilled water |K,SO, in Nessler cylinder labelled as
and transfer in a Nessler cylinder. |'Standard’. Add about 10 ml of distilled
Labelled as ‘Test’ water.

9, |Add 2 ml of dil. HCl Add 2ml of dil. HCl
3, | Diluted with 45 ml distilled water | Dilute with 45 ml with distilled water

4, |Add 5 ml of 'BaSO, reagent’ Add 5 ml of “BaSO, reagent’

Stir each solution with separate glass rods and allowed stand for 5 minutes. Compare the

 

 

 

 

 

turbidity transversely against a dark back ground to have a better contrast for
comparison..

OBSERVATION :

» The opalescence in the sample is less than the standard-It passes the test,It is standard
>» The opalescence in the sample is more than the standard-It fails the test,It is Sub standard

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PHARMACEUTICAL ANALYSIS UNIT - I

LIMIT TEST FOR IRON
REQUIREMENTS
Chemical required: Thioglycolic acid, citric acid, Ammonia solution, ferric ammonium sulphate

Principle :
» The limit test of iron is based on the reaction between iron and thioglycolic acid in the presence
of citric acid in a ammonical solution.
> Citric acid prevents precipitation of iron with Ammonia.
» A deep reddish purple colour is formed. Ferrous thioglycolate is colourless in acidic medium but
in alkaline medium it gives purple colour.

2 +
Fe + + 2SHCH,COOH  ------------+-------22-0000 > Fe (SHCH,COO), + 2H

( Thioglycollic acid ) ( Ferrous thioglycollate complex)

Note:
1.Citric acid react with ammonia solution, giving ammonium citrate, which act as a buffer.

2.The citrate ions also prevent the precipitate of iron with ammonia by forming complex with it.

3.Thioglycollic acid not only react with ferrous ions, but also reduce ferric ions to ferrous ions
PROCEDURE:

 

 

Sl [TEST STANDARD
INO
1 Place specified amount of test Place 2 ml of standard solution in a
sample in a Nessler cylinder INessler cylinder labelled as standard

labelled as ‘Test’ and diluted to 40 land diluted to 40 ml with distilled water
im! with distilled water

2 |Add 2 ml of 20% w/v of iron free [Add 2 ml of 20% w/v of iron free citric
citric acid. lacid.
3 |Add 0.1ml of thioglycollic acid. [Add 0.1ml of thioglycollic acid
4 IMake the solution alkaline with Make the solution alkaline with iron free
iron free ammonia solution. lammonia Solution.

5 Dilute to 50 ml with distilled water IDilute to 50 ml with distilled water

 

 

 

 

 

Stir each solution with separate glass rods and allow to stand for 5 minutes. Compare the colour

produced in the two Nesslers cylinder by viewing vertically downwards.

OBSERVATION :

» The Purple colour in the sample is less than the standard-It passes the test,It is standard
>» The Purple colour in the sample is more than the standard-It fails the test,It is Sub standard

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PHARMACEUTICAL ANALYSIS UNIT - I

LIMIT TEST FOR LEAD

Principle :

» Limit test for lead is based on the reaction of lead and diphenylthiocarbazone (dithizone) in
alkaline solution to form lead dithizonate complex which is violet in color.
» In this test, Nessler cylinders are not used, instead it is performed by extraction with the help of

separating funnel.

IS Dwimsrwee ew rae ~td G H N 3
SHNHG es NH.NHG¢ he J oe SN N
Pb? + S=< KY, S==C Pb C= Ss
\ \
N=N.C,H. Niieg 6.46 / CgHs HN.HN
Note:

» The original color of dithizone in chloroform is green while the lead dithizonate complex is violet

in color.

Vv

medium.

The intensity of violet color depending upon the quantity of lead present in the solution.
Intensity of this violet color in both test and standard are compared in a chloroform solvent

» The interference & influence of other metal ion is eliminated by adjusting the optimum ph for the
extraction by using ammonium citrate,potassium cyanide,hydroxylamine hydrochloride reagents

 

 

 

 

 

 

etc...
PROCEDURE:
S.NO TEST STANDARD
1. A Known quantity of sample A Standard lead solution is prepared equivqlent to
solution is transferred in separating the amount of lead permitted in the sample under
funnel examination
2. Add 6 ml of ammonium citrate Add 6 ml of ammonium citrate
3. Add 2 ml of potassium cyanide & 2 Add 2 ml of potassium cyanide & 2 ml of
ml of hydroxylamine hydrochloride hydroxylamine hydrochloride
4. Add 2 drops of phenol red Add 2 drops of phenol red
5. Make solution alkaline by adding Make solution alkaline by adding ammonia solution
ammonia solution
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PHARMACEUTICAL ANALYSIS UNIT - I

 

 

 

 

 

 

 

 

 

6. Combine dithizone extracts are Combine dithizone extracts are shaken for 30 sec
shaken for 30 sec with 30ml of 1.0% with 30ml of 1.0% nitric acid and the chloroform
nitric acid and the chloroform layer layer is discarded

is discarded

7. To the acid solution add 5 ml of To the acid solution add 5 ml of standard dithizone

standard dithizone solution solution

8. Add 4 ml of ammonium cyanide Add 4 ml of ammonium cyanide

9. Shake for 30 sec Shake for 30 sec

OBSERVATION :

» If color produced in the test solution is less than the standard solution the test solution is passed

limit test.
» If color produced in the test solution is more than the standard solution the test solution is failed
limit test
LIMIT TEST FOR ARSENIC
Principle :

>» The limit test for arsenic is based on the reduction of the arsenic into arsenious state to
the arsenic gas (ASH3) with zinc and hydrochloric acid.
>» The arsine gas stains the mercuric chloride paper yellow.

Reaction :

» The sample is dissolved in acid, the arsenic present in the sample gets converted into
arsenic acid.

>» The arsenic acid is reduced to arsenious acid by reducing agents like stannous acid,
potassium iodide etc.

>» The nascent hydrogen is formed during the reaction of reducing arsenious acid to arsine
gas.

>» The arsenic gas reacts with mercuric chloride paper to produce yellow stain.

As* —+  H;As0,
(impurity) (Arsenic acid)
HjAs04 - H3As03
(Arsenic acid) (Arsenious acid)

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PHARMACEUTICAL ANALYSIS UNIT - I

 

 

 

 

 

H3AsO3, + 3H» _- AsH3 + 3H20
(Arsenious acid) (Arsine gas)
2AsH; +H gCl, > (AsH)> +2HCl
(Arsine gas) (Mercuric chloride) (yellow stain)
S. No. TEST STANDARD
1. The test solution is prepared by dissolving A known quantity of dilute arsenic
specific amount in water and stannated HCl solution is kept in wide mouthed bottle
and kept in a wide mouthed bottle. and rest procedure is followed as
described in test solution.
2. To this solution | gm of KI, 5 ml of stannous To this solution | gm of KI, 5 ml of
chloride acid solution and 10 gm of zinc is stannous chloride acid solution and 10 gm
added (all this reagents must be arsenic free) of zinc is added (all this reagents must be
arsenic free)
3. Keep the solution aside for 40 min and stain Keep the solution aside for 40 min and
obtained on mercuric chloride paper is stain obtained on mercuric chloride paper
compared with standard solution. is compared with standard solution.

 

 

 

 

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PHARMACEUTICAL ANALYSIS UNIT - I

IMPORTANT QUESTIONS

10 MARKS :

1.What is Error? Explain in detail about the sources of error & types of error.Write
a note on minimization of errors.

5 MARKS :
1.Write a note on different analytical techniques.
2. Explain various methods of Expressing concentration of standard solution.

3.Write the preparation & standardization of potassium permanganate with
principle and reaction.

4. write the preparation & standardization of ceric ammonium sulphate.
5. write the preparation & standardization of sodium hydroxide.
6. write the preparation & standardization of HCL with principle and reaction.

7. write the preparation & standardization of sodium thiosulphate with principle
and reaction.

8.Write the preparation & standardization of Sulphuric acid with principle and
reaction.

9 .Limit test for chloride,sulphate,iron,arsenic,lead.

2 MARKS QUESTIONS:

 

1.Define pharmaceutical analysis & its types
2.scope of pharmaceutical analysis
3.primary standard & its example

4. secondary standard & its example.

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PHARMACEUTICAL ANALYSIS UNIT - I

5.Define Molarity

6. Molality

7.Normality

8.Formality

9.Define saturated solution.

10.accuracy

11. precision

12.significant figures.

13.Define impurities& sources of impurities
14.pharmacopoeia

15.Limit test

16.Write about quantitative and qualitative analysis.
17. Preparation of 0.1N Oxalic acid.

18. Write about personal errors.

19. Define Errors.

20.Types of error.

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ACID BASE TITRATION (NEUTRALIZATION TITRATION) UNIT-II
SYLLABUS :
ACID BASE TITRATION

Theories of Acid Base Indicators, Classification of acid base titrations and theory involved in titration s of

strong ,weak, and very weak acids and bases, neutralization curves.
ACID BASE TITRATION

DEFINITION :
A Procedure used in quantitative chemical analysis to determine the concentration of either acid or a base.
A quick and accurate method for determining acidic or basic in many sample.

Titrant is the solution added from the burette.

The equivalent point is the point at which the amount of acid and base present exactly neutralizes one another.
(number of moles of OH - ions and number of moles of H + ions are equal)

Indicator is a substance that is generally added to the solution in the receiving vessel an which undergoes some
sort of colour change when reaction is over.

The end point of titration is the point when the indicator changes colour.
ACIDS: Substance that issloved in water to produce H + Ions

BASES: Substance that dissolve in water to produce OH- Ions.

ermlmlUEleEEET
Properties of:
Acids Bases
1. Sour taste 1. Bitter taste
2. Conducts electricity 2. Feels slippery
3. Turns litmus paper 3. Conducts electric
red current
4. Reacts with bases 4. Turns litmus paper
to produce salts blue
and water 5. Reacts with acids to
5. Reacts with some produce salts and
metals and releases water

hydrogen gas

48, og
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ACID BASE TITRATION (NEUTRALIZATION TITRATION) UNIT-II
Theories:
There are three theories which explain the concepts of acid and bases..
1.Arrhenius theory
2.Bronsted-Lowry theory
3.Lewis theory
CONCEPT OF ACID AND BASE

There are number scientist framed the concept of acid and base, but they failed to prove. Finally Arrhenius
framed a successful concept of acid and base.

ARRHENIUS CONCEPT :
They defined acids and bases interms of the effect of the substance in water.

ACID:
A Substance when dissolved in water, it relese hydrogen ions [H+] in water. (or) it increase the
concentration of hydrogen ion.

Eg: HCl ~~ ----- > H+ + Cl-
BASE:

A substance when dissolved in water, it relese hydroxy] ion[OH-] in water. (or) it increase the concentration of
hydroxy ion.

Eg: NaOH ----- > Nat + OH-
The hydrogen ion is not a bare proton but it chemically bonded to water ie, H30+(hydronium ion) Eg: perchloric
acid.
HCIO4 + H20 wenn nen nne== > H30+ + Clo4
Arrhenius Acid
Any substance that releases hr’ ions as the
only positive ion in the aqueous solution

® DP QM:

HCl H,O H,O' cl

 

hydrogen chloride water hydronium ion ohloride ion

(an Arrhenius acid)

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ACID BASE TITRATION (NEUTRALIZATION TITRATION) UNIT-II

PU dite dA LO LSB sy ate) at

H,O > ' a)
—a CO + ae
Potassium Hydroxide
H,O
ti OH ee £ Fe. + OH

 

Lithium Hydroxide

ADVANTAGES:

» It is the first scientific theory giving definitions for acid and base.
» It classifies acids and bases according to their strength.

» It is characterized by simplicity.

» It is helpful in aqueous media.

LIMITATIONS OF ARRHENIUS CONCEPT

FREE H+ AND OH- IONS DO NOT EXIT IN WATER

Â¥ The ions[H+] and [OH-] produced by acid and base are do not exit in water in the free state. It associate with
water molecule to form complex ion through hydrogen bonding.
Â¥ Similarly, OH- ions form complex of H302-

— oe Ei ?
H =<OG}+ Ht — |" F2 =O:
ae Proton
Ei
Water Hydronium tom

H—O-— HH
4
Fi

HMydrormiurm tom

50
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ACID BASE TITRATION (NEUTRALIZATION TITRATION) UNIT-II
i) LIMITED TO WATER ONLY:
Here they explain the acid and base in water only. But acid and bases are appropriate to other solvents also.
iii) SOME BASES DO NOT CONTAIN HYDROXY ION[OH-] :

Arrhenius base- produce OH- ion in water. But there are compounds like Ammonia(NH3) and Calcium oxide(CaO)
are bases but contain no OH- ions

iv IT CANNOT EXPLAIN THE ACIDIC CHARACTER OF SOME SALT:

Eg: AIC]3 is a salt — in aqueous solution they fails to explain the acidic character of aluminium chloride.
BRONSTED-LOWERY CONCEPT

ACID:

Any molecule or ion that can donate a (H+)proton. (OR) A substance which has tendency to loss a proton.
BASE:

Any molecule or ion that can accept a proton. (OR) A substance which has tendency to gain a proton.
Simply,

ACID — “Proton donar� ; BASE — “Proton acceptor�

a

[email protected]® .- —_ @ - &@®

; Conjugate Conjugate
ane nase Base Acid
Reactants Products

Bronsted-Lowry Acid-Base Reaction

CONJUGATE ACID BASE PAIRS:

In an acid base reaction the acid[HA] gives up its proton [H+] and produce a new base[A-]. A new base that related to
the original acid is called conjugate base.

The base accepting a proton [H+] gives a new acid HB is called conjugate acid.

A hypothetical reaction between the acid HA at the base B- Will illustrate the above definiions.

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ACID BASE TITRATION (NEUTRALIZATION TITRATION) UNIT-II

| Conjugate Acid-Base Pair
A

 

 

 

f 1
Bronsted-Lowry Conjugate
Base Acid

 

 

 

 

 

 

cents :

sa] - ® —: @®@ -: &®
“> |

Bronsted-Lowry Conjugate
Acid Base

L J
T

 

 

 

 

Conjugate Acid-Base Pair ©

EXAMPLES OF CONJUGAE ACID-BASE PAIRS:
1.Reaction of ammonia ( NH3) with water ( H20 )

acid conjugate
| base

NH; + H;0 —» NH, + OH

| |

base conjugate
acid

+ In this reaction , NH3 accepts a proton from H20.

« Thus NH3 is a base and H20 is an acid.

« In the reverse reaction , NH4+, donates a proton to OH-.
« The NH4+ ion is the acid and OH- is the base.

NOTE:

Â¥ NHs and NHz-+ differ by a proton.That is NH; becomes the NHg+ ion by gaining a proton.where
as
> NH,+ ion becomes the NH, molecule by losing a proton.
» The species NH,+ and NH are a conjugated acid base pair.
>» A conjugated acid base pair consists of two species in an acid —base reaction,one acid and one base,that
differ by the gain or loss of a proton.

52

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ACID BASE TITRATION (NEUTRALIZATION TITRATION) UNIT-II

ADVANTAGES OF BRONSTED LOWERY CONCEPT:

i)Has much wider scope because it embraces all molecules and ions that can donate proton and accept the proton.

ii)Not limited to aqueous solution.
Eg: NH3 + HCl — ----- > NH4+ + Cl-
iii)Relese of OH- not necessary to qualify as a base.
Eg: NH3 + H+ = ------- > NH4+
(ammonia)

LIMITATIONS OF BRONSTED CONCEPT

i)It cannot explain the reaction between acidic oxides like CO2, SO2, SO; etc... and basic oxides like CaO, BaO,

Mg0 etc which take place even in the absence of the solvent.
ii)Substance like BF3,AICl; etc..behave as acid but they do not have proton to loose or donate.

LEWIS CONCEPT

Â¥ The acid and base concept of bronsted and lowery are further extended by G.N.Lewis.
v¥ They include many organic and inorganic reaction in which a proton is not involved.
Â¥ Lewis proposed the acid base concept by the electron pair theory of covalent bond.

ACID(LEWIS ACID) — Any species(molecule or atom or ion) which can accept a lone pair of electron to form
covalent (or) coordinate bond. (or) simply ACID is an electron pair acceptor.

Lewis acid are electrophilic.

Eg: all cations — Al3+,Mg2+,Cu2+,H+,7n2+.

BASE(LEWIS BASE) - Any species which can donate a lone pair of electrons to form covalent or coordinate bond.

(or) simply BASE is an electtron pair donor.
Lewis base are nucleophilic.

Eg: all anions — SO4-,Cl-,Br-,02-.

——
x + -B > A B

Lewis Acid lewis Base coordinate
covalent bond

 

(Electron (Electron
Acceptor) Donor)

53 . .
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ACID BASE TITRATION (NEUTRALIZATION TITRATION) —_ UNIT-II
EXAMPLES FOR LEWIS CONCEPT

1.REACTION BETWEEN BF3 AND NHsa:

Lewis Concept of Acids and Bases

@ The reaction of boron trifluoride with
ammonia is an example.

: i: 7 Say 1
[F—B + :N—H — :--F— B — N—H

| | | |

a H =F: H

Boron trifluoride accepts the electron pair, soitisa
Lewis acid. Ammonia donates the electron pair,
so itis the Lewis base

 

1

 

BF3 has 6 valence electrons with B atom which can accept an electron pair and is a Lewis acid. The N atom of

NH3 has a lone electron pair and is a Lewis base.

2.REACTION BETWEEN H+ and NH3:

H H
| = 3 si
H—N: + H—O: — H-—N—H + :O2
H H H H
Hydrogen Hydrogen
ion acceptor: on donor
B-L base B-1 acid

ADVANTAGES:

>» All transfer or gain of a proton in bronsted acid base reaction are accompained by the loss or donation of

an electron pair of the reaction.
» More reactions of the reactants which do not have proton are involve in the acid base reaction.

Eg: BF3 + NH3 2 wee > BF3 — NH3

LIMITATION:

Â¥ Relative strengths of acids and bases are not explained by lewis.
Â¥ It does not explain the behaviour of well known protonic acid like HCl, H2S04 etc.. Which do not form

covalent bond with bases.

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ACID BASE TITRATION (NEUTRALIZATION TITRATION) UNIT-II

OVERVIEW OF THE THREE THEORIES

 

 

 

 

 

 

 

S.NO THEORY ACID BASE
1. Arrhenius Theory H+ Producer OH - Producer
2. Bronsted-Lowry Theory H+ Donor H+ Acceptor
3. Lewis Theory Electron pair accepor Electron pair donor

 

 

 

BUFFER
A solution has ability to resist changes in pH of the solution when limited amount of acid or base are added to it.
i)ACIDIC BUFFER:

YA Buffer solution which has a pH less than 7.
Â¥ These solution are commonly made from a weak acid and it salts.
Â¥ Eg: acetic acid and sodium acetate.

ii)BASIC BUFFER:

YA Buffer solution which has a pH more than 7.
Â¥ These solution are commonly made from a weak base and it salts.
Â¥ Eg: ammonia and ammonium chloride.

INDICATOR
Â¥Y An indicator is a substance which is used to determine the end point in a titration

Â¥ In acid-base titrations, organic substances (weak acids or weak bases) are generally used as indicators.
Â¥ They change their colour within a certain pH range.

ACID — BASE INDICATORS (NEUTRALIZATION INDICATORS)

COMMENLY USED ACID BASE INDICATOR:

 

 

 

 

 

 

 

 

 

 

INDICATOR PH Range Colour change
Methyl orange 2.9-4.0 Red to yellow
Methyl] red 42-63 Red to yellow
Congo red 3.0-5.0 Blue to red
Phenolphthalein 8.3 — 10.0 Colourless to red
55

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ACID BASE TITRATION (NEUTRALIZATION TITRATION) UNIT-II
METHYL ORANGE:

It used in assay of strong acid.

PREPARATION :0.1G methyl orange + 80ml water +95%ethanol 100m]
pH RANGE : 2.9-4.0
COLOUR CHANGES : red to yellow

the yellow form of methy! orange

0 GH3
4
"O-§ MoM No

al CHg

METHYL RED:
It used in assay of weak base. Eg : ammonia and amines.
PREPARATION ‘50mg methyl red + 1.86ml 0.1M NaOH +50ml1 95% ethanol+100mlwater.
pH RANGE 74.2-6.3

COLOUR CHANGE : red to yellow.

 

CONGO RED
pH RANGE :3.0-5.0

COLOUR CHANGE : Blue to red

NH> NH>2
Core OO"
ee [email protected]
SO 3Na SOsNa

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ACID BASE TITRATION (NEUTRALIZATION TITRATION)

PHEOLPHTHALEIN

UNIT-II

This is typical indicator, most commonly used in acid base titration.

PREPARATION :1g phenolphthalein + 10ml 95%ethanol + 100ml water.

pHRANGE _ :8.3TO 10.0

COLOUR CHANGE : colourless to pink

   

N, _H,SO,(conc)
(-H,0)

OL

O
|

Qa

ge
OO

Phenolphthalein

Phthalic anhydride react with phenol in the presence of conc.sulphuric acid forms a phenolphthalein

Phenolphthalein's common use is as an indicator in acid-base titrations.It is a white crystalline powder.It is insoluble

in water,but readily soluble in alcohol.

THEORY OF INDICATORS

An acid base indicator is a substance which a possesses one colour in acid solution and a different colour in alkaline

solution.
Two theories explain these colour changes

Â¥ Ostwald theory
Â¥ Quinonoid theory

OSTWALDS THEORY:

It based on ionization reaction.

VVV WV

According to this theory, colour of a solution is due to coloured ions.
Indicators are either weak organic acid or weak organic base.
Undissociated molecule has a different colour from dissociated ions.

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ACID BASE TITRATION (NEUTRALIZATION TITRATION) UNIT-II
EXAMPLES :
PHENOLPHTHALEIN(Hph):

> Itis a weak acid.
> Undissociated molecule is colourless
> Dissociated H* ions — colourless, ph ions — pink or red colour.

Hph __ ---------- > H+ + ph-
(colourless) (colourless) (pink)

> In presence of acid ,due to an increase in conc of H* ions ,then the solution remain colourless.
> In presence of base -- OH ions forms it combine with H* ions from phenolphthalein to form freely
ionized water.

-- ph ions so produced combine with Na+ ions to forms strongly ionized sodium salt(Naph) and thus
remain in solution in the ionc stage and impart a pink colour.

HPA === H* + PA

 

NaOH = OH +Na~

Jf Jt

H>5O NaPA

(feebly ionised) (ionised)

 

METHYL ORANGE(MeOH):

 

v¥ Itis weak base
Â¥ Unionized molecule is yellow.

¥ On ionization — OH- ion — colourless , Me+ ions — red.
¥ In acid solution — red colour

¥ In base solution — yellow colour.

MeOH <== Meâ„¢ + OHâ„¢

 

HClL =}Cr i
MeCl HOH
(Strongly ionised) (Feebly tonised)

58
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ACID BASE TITRATION (NEUTRALIZATION TITRATION) UNIT-II

QUINONOID THEORY :
This theory is based on chromophores which is responsible for imparting colour to a compound.
CHROMOPHORE - Greek word — ‘colour carrier’.

Eg: C=C,C=0,C=N,N=N,N=O0
Most of the indicators are organic aromatic derivatives.
So, the colour changes are basis of intermolecular change .
It is indicated by two tautomeric forms.

> Benzenoid form
> Quinonoid form

One form exit in acid solution.

One form exit in basic solution.

CH —CH —
_ 4“ \ J CH=CH \
\ cC— <=> — ——
CH —=cH�~ Nc cH�
Benzenoid form Quinonoid form
(colourless) (coloured)

EXAMPLE P- NITRO PHENOL:
In acid —  benzenoid form — colourless.

In alkaline - Quinonoid form — yellow colour.

im
HO {' nw, = rom ae RO, (Deep Yellow)

59

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ACID BASE TITRATION (NEUTRALIZATION TITRATION) UNIT-II

PHEOLPHTHALEIN:

The indicator phenolphthalein is colourless in the acid form (benzenoid form ) but possess as a red or pink colour in
the tauomeric form which exists in an alkaline solution (Quinonoid form)

ae vi OH
om A ) |
| ~

Zo ~< base oe
SS Ae ie ‘eid SS

C—OH
ll
f oO
enoid structure Quinonoid structure
Ber eoiouriess) (rad or pink coloured)

METHYL ORANGE:

Methyl orange has quinonoid form in acidic solution and benzenoid form in alkaline solution. The color of benzenoid
form is yellow while that of quinoniod form is red.

 

onâ„¢ mK J CHa
O38—< > hit — i < > == NK
[ a —_ nN CHs
Quinonoid form — Acidic solution (red) "
OQ eis
“ye

CH-

— i ~ pore
-038— > — N= N— 6 pp - N«<
. 4 V4 Nos

TYPES OF TITRATION
The pH value at the endpoint is depends upon the relative strength of acid and base.
Based on these, they explain in four types of titration ,

Neutralization of strong acid with strong base.
Neutralization of weak acid with strong base.
Neutralization of weak base with strong acid.
Neutralization of weak acid with weak base.

VVV WV

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ACID BASE TITRATION (NEUTRALIZATION TITRATION) UNIT-II

NEUTRALIZATION OF A STRONG ACID WITH A STRONG BASE
In this type of titration,

Strong acid — hydrochloric acid

Strong base — sodium hydroxide.

When both acid and base are titrated it completely dissociate.

Neutralization of strong acid and strong base occur at the laboratory temperature.

Eg: HCl + NaOH  --------- > NaCl + H20

strong acid (HC!) v. strong base (NaOH)

4S
12

10 4

   
 

Adding 0.1M NaOH
to 25 mL of 0.1M HCI

PH 1 at the stort
due to 0.1m HET 5

(atrong T T T T t T T T
monoprotic acid) 5 10 Ss 20 25 30 35 40

Volume of alkali added / cm?

 

 

strong acid (HC!) v. strong base (NaQH)

 

 

14- :

12 +

10 +

= 8 Adding 0.1M NaOH
6 to 25 mL of 0.1M HCI
4
Very little pH change
2- during the initial 20 mL 4
o T T T T it T T T

 

5 10 15 20 25 30 35 40
Volume of alkali added /cm?

61
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ACID BASE TITRATION (NEUTRALIZATION TITRATION)

strong acid (HC!) v. strong base (NaOH)

14-

Curve levels off at pi 13
due to excess 0.1M NaOH
(a strong atkall)

 

 

 

o T T T T t T T T
5 10 15 20 26 30 35 40

Volume of alkali added /cm?

strong acid (HC!) v. strong base (NaOh)

14
12

10

   
 
     

Very sharp change in pH
ever the addition of less
then hell «a drop of Neor

Qo

a

Nn

*
:
T+ YS 18
5 10 16 20 26 30 35 40

Volume of alkali added /cm?

The graph shows the curve for titration of 25.0m1 of 0.1M HCI with 0.1M NaOH.
pH changes slowly first.

Near the equivalent point — moles of NaOH equally added to moles of HCl.

At equivalence point — no.of moles of NaOQH= no.of moles of HCl.

Therefore, pH of solution is 7.

Further addition of acid or base — pH rapidly changes about pH — 11.

To detect the end point we add an indicator.

It changes colour within the pH range (3.0-11.0).

LLL KKK KS

If colour changes occur on basic side use

PHENOLPHTHALEIN- it changes from colourless to pink in pH (8.2-10.0).
If colour changes occur on acidic side use

BROMOCRESOL GREEN - colour chances in pH (3.8 - 5.4)

62

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ACID BASE TITRATION (NEUTRALIZATION TITRATION) UNIT-II
NEUTRALIZATION OF A WEAK ACID WITH A STRONG BASE
In this type of titration,

» weak acid — acetic acid
> Strong base — sodium hydroxide.

The titration curve start at higher pH than HCl. Because acetic acid is weak acid.
The pH range is shorter than strong acid vs strong base.
Eg: CH3COOH + NaOH_ --------- > CH3COONa~ s+ H20

weak acid strong base salt of weak acid

WEAK ACID Vs STRONG BASE

 

104 Phenoiphthalein

| “—~ pH = 8.80 at
equivalence
point

    
 

pK. of CH3CH2COOH=4.89

ST
gion
et FS
2

—
â„¢~

  
   
 

oH

Methyl! red

[CH3CH2COOH] = [CHsaCH2COo7]

 

 

 

o ' ' ' ' t ' t '
10 20 30 40 50 60 7o 80

Volume of NaOH added (mL)

Titration curve shows, titration of 25.0ml of 0.1M acetic acid and 0.1M NaOH.

The pH changes slowly first, then rapidly near the equivalence point.
The end point shows at pH (7 to 11).
Phenolphthalein Would work it changes colour in the pH range (8 to 10.0).

LLRKKR SK

5.4).
The equaivalence point for the titration curve of acetic acid occurs at basic side.
It changes colour within the pH range (7.0-11.0).

<M

The indicators used in this type of titration are

 

Phenolphthalein, Thymolphthalein, Thymol blue

63

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The Titration starts at a higher pH than the titration of HCL because of acetic acid is a weak acid.

But, methyl orange,methy] red, bromocresol green are not work because of the pH (2.8 — 4.6,4.2 — 6.3, 3.8 -

 
 

 

ACID BASE TITRATION (NEUTRALIZATION TITRATION) UNIT-II
NEUTRALIZATION OF A WEAK BASE WITH A STRONG ACID
In this type of titration,

v¥ Weak base — ammonia.
¥ Strong acid — hydrochloric acid.

The titration curve similar that of weak acid with strong base, but the pH decline.
Neutralization of weak base and strong acid occur at the laboratory temperature.

Eg: NH,OH + HCl © --------- > NH,Cl + H,0

WEAK BASE Vs STRONG ACID

POH of NHs = 4.75

   
 

Methy! red

 

 

 

o T T T T T T
10 20 30 40 50 60 7o 80

Volume of HC! added (mL)

The curve shows pH changes during the titration of 25.0ml of 0.1M Ammonia by 0.1M HCl.
pH declines slowly first, then falls rapidly from pH 7 to 3.

Methyl red — colour changes from yellow at pH 6.0 to red at pH 4.8.

Phenolphthalein, thymolphthalein are used in this titration.

The end point occurs at pH- 5.3.

So, the indicator used in these pH range (3.0 — 6.5).

LLRKKR SK

Eg: methyl orange
methyl] red
bromophenol blue
bromocresol green

64

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ACID BASE TITRATION (NEUTRALIZATION TITRATION) UNIT-II
NEUTRALIZATION OF A WEAK ACID WITH A WEAK BASE
In this titration,
¥ weak acid — acetic acid. Weak base — ammonia.

Titration curve for the neutralization of 25.0ml of 0.1M acetic acid with 0.1 M aqueous ammonia at the lab
temperature.

In curve, there is no sudden changes in pH and hence no sharp end point can be found with simple indicator.
A mixed indicator which exhibits sharp colour changes.
Eg: neutral red — methylene blue

CH;COOH + NH,OH ---> CH;COONH, +H;0

weak acid (CH,COOH) v. weak base (NH,)

     
   
 

‘
:
12-4 ; Curve levels off at pH 10
‘ due to excess 0.1M NH,
‘
a weak alkali)
104 : ¢
‘
8 ‘
= ] NO SHARP
6+ Steady pH change CHANGE IN pH

‘
‘

‘

‘

pH 4 due to 0.1m 4 :
CH,COOH (weak :
monoprotic acid) o-] ‘
:

‘

4

T

 

 

or TT TT Tc. '
5 10 15 20 25 30 35 40

Volume of alkali added / cm?

IMPORTANT QUESTIONS:
10 Marks

1. What is a neutralization curve? Explain the types of neutralization curve with
examples.

2. Explain about theories of acid base indicators.(or) Explain the choice of Indicators in
acid —base titration.

5 Marks

1. Explain the various concepts of acid base titration

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ACID BASE TITRATION (NEUTRALIZATION TITRATION) UNIT-II

2 Marks :
1. Define Acid and Base
2.Write properties of Acid and Base
3.Define Levelling effect
4.Define Alkalimetry and Acidimetry
5. DefineTitration
6. Define neutralization
7.Define acid base titration
8.Define Buffer with examples
9.Give the examples indicators used in acid base titration
10.Neutralisation curve or titration curve

11.Write down the classification of acid and base tirations

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NON AQUEOUS TITRATION — UNIT-II

Syllabus:

Solvents, acidimetry, and alkalimetry titration and estimation of Sodium benzoate and
Ephedrine HCl

DEFINITION:

> It is the titration of substances dissolved in solvents other than water.
>» It is suitable for titration of very weak acid and very weak bases.

LIMITATIONS OF ACID BASE TITRATION

Â¥Y It is impossible to define the substance which are insoluble in water.

Â¥ It is impossible to titrate for a mix of acids or the bases.

Â¥ The substance which are too weakly acidic or too weakly basic cannot give sharp end point in
water.

ADVANTAGES OF NON AQUEOUS TITRATION

This titration is simple and accurate.

Organic acid and base that are insoluble in water are soluble in non aqueous solvent.
In a mixture of acid, an individual acid can separate end point in different solvents.
Weak acid and weak base can easily titrated.

Titration of water sensitive drugs (eg: aspirin, chloramphenicol)

SLR KK

THEORY:
ARRHENIUS THEORY:

> Neutralization of acid and base occurs in water, when solvents other than water is feasible.
> So, It cannot be applied for this.

BRONSTED THEORY:

» In aqueous solution, neutralization interpreted by proton donar and proton acceptor.
» It depend on the choice of solvent
>» The titration of aq. Solution of an amine (R3N) with an aq. Solution of an acid( HA).

HA + H,O ------ > H;0+ + A- (aq. Acid)
R3N + H,0 ------- > OH- + R3NH+ (aq. Amine)
H,0+ + OH- ------ > 2H,O
The summation of these equation indicates, water is not essential for the reaction.
Te, HA + R3N ------- > R35NH+A-

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NON AQUEOUS TITRATION — UNIT-II
LEWIS CONCEPT:
Electron Acceptor ---ACID
Electron Donor ----- BASE
TYPES OF SOLVENTS :( IMPORTANT 5 MARK)
Based on proton transfer,solvents are divided into four types
APROTIC PROTOPHILIC PROTOGENIC AMPHIPROTIC
1.Aprotic are substance | These are basic in character | It is acidic in nature. It They have both

which are chemically
neutral (or inert)

2.This type of solvent
neither accept nor
donate proton.

3.Used to dissolve
water insoluble drugs

Eg: Benzene,
acetonitrile,
chlorobenzene,
chloroform, carbon
tetrachloride, dioxin,
ethyl acetate, toluene.

 

and react with acid to form
solvated proton

Weakly basic solvent — less
tendency — accept proton
than strong basic.

Weakly acidic solvent —
less tendency — donate
proton than strong acid.

Used to dissolve acidic
analyte

Eg.acetone, ether, pyridine,
liquid
ammonia,ethylene,diamine

 

readily donate proton

ability to donate protons

Used to dissolve basic
analytes

Eg. sulphuric acid,
formic acid, propionic
acid, acetic anhydride
etc.

 

protophilic and
protogenic properties

They can accept and
donate protons.

Act as a weak acid &
weak base

Eg.Water, alcohols,
acetic
acid,ethanol,methanol

 

 

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NON AQUEOUS TITRATION — UNIT-II

 

ACIDIMETRY

ALKALIMETRY

 

 

» Used for quantitative estimation
of basic drugs
>» Acidic in nature

SOLVENTS USED IN
ACIDIMETRY

].Neutral solvents

v They are aprotic or amphiprotic in

nature.

v They do not enhance dissociation.
Eg: acetonitrile, alcohol, chloroform,
benzene, chlorobenzene, dioxin and
ethyl acetate.

2.Acidic solvents

Vv They are protogenic in nature.

Y It used for weak bases and their
salts.

v Eg: Formic acid, glacial acetic
acid, propionic acids, acetic
anhydride and sulfonyl chloride.

3. Mixture of base

v such as ethylene diamine and
theophylline two solvents are
used.

v Eg: Acetic acid with perchloric
acid — only ethylene diamine is
reacted.

¥ Upon adding acetic anhydride —
theophylline get reacted.

Y Potentiometer is used to detect

both end points.
69

 

» Used for quantitative estimation
of acidic drugs
>» Basic in nature

SOLVENTS USED IN
ALKALIMETRY

1.Basic solvent

v Ethylene diamine, n —butylamine,
morpholine-[strong base].

Y Used in titration of weak acids.

Â¥ Dimethyl formamide, anhydrous
pyridine — [weak base].

Y Used in titration of medium

strength acidic substance.

 

 

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NON AQUEOUS TITRATION — UNIT-II

 

 

TITRANT USED IN ACIDIMETRY

TITRANTS USED IN

 

1.Perchloric acid in acetic acid

For amines, amine salts, amino acids,
salt of acid.

2.Potassium methoxide in toluene-
methanol

Quan ammonium hydroxide in
acetonitrile-pydridine.

3.For acids, imides, sulphonamides.

INDICATORS USED IN
ACIDIMETRY

1.For weak bases,

Oracat blue, crystal violet, methyl
rosaniline chloride, quinaldine red, 1-
naphtholbenzein, malachite green.
2.For strong bases,

Methyl red, methyl orange and thymol
blue.

Crystal violet

70

 

ALKALIMETRY

SODIUM METHOXIDE — produce
gelatinous precipitate.

POTASSIUM METHOXIDE - stronger
titrant — not used.

LITHIUM METHOXIDE IN
TOLUENE METHANOL - used.
SODIUM TRIPHENYL METHANE —
used for weakly acidic
compound(phenol).

TETRABUTYL AMMONIUM
HYDROXIDE IN MATHANOL - used
for very weakly acidic compound
(hydrochlorothiazide).

INDICATORS IN ALKALIMETRY

 

AZO VIOLET - weak acid
THYMOL BLUE

O- NITRO ANILINE
THYMOLPHTHALEIN AND P-
HYDROXY AZOBENZENE

 

 

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NON AQUEOUS TITRATION — UNIT-II

 

 

PREPARATION OF 0.1M
PERCHLORIC ACID

Slowly add 8.5ml of perchloric acid to
500ml anhydrous glacial acetic acid
with continuous mixing.

Add 25ml of acetic anhydride and cool

it. \

Add anhydrous glacial acetic acid to
produce 1000ml.

V

Allow to stand for 24 hours

STANDARDIZATION OF
PERCHLORIC ACID:

Weigh 0.7g of potassium
phthalate(previously dreid at 120°C for
2 hours)

v

Dissolve in 50ml of glacial acetic acid.
Add 2 drops of crystal violet
v

Titrate with 0.1M perchloric acid
Colour changes from violet to emerald

green. |

Each Iml of 0.1M perchloric acid is
equivalent to 0.02042¢ of KHP

71

 

SODIUM METHOXIDE
PREPARATION OF 0.1M SODIUM
METHOXIDE IN TOLUENE —
METHANOL:

Cool 150ml of anhydrous methanol in
ice water. i

Add 2.5g sodium in to methanol.

When sodium dissolved, add sufficient
toluene to make upto 1000ml.

Standardize the solution.
Prepare the solution immediately before

use.
On storage it may lost its effectiveness.

STANDARDIZATION OF 0.1M
SODIUM METHOXIDE:
Weigh 0.4g of benzoic acid

Vv

Dissolve in 80ml of dimethyl
formamide
Vv

Add 0.15ml ay thymolphthalein solution

Titrate against, with 0.1M sodium
methoxide v

Appearance of blue colour
Perform the blank determination.

Each Iml of 0.1M sodium methoxide is
equivalent to 0.01221¢ of benzoic acid.

 

 

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NON AQUEOUS TITRATION — UNIT-II

 

 

ASSAY OF EPHEDRINE HCL

Weigh 20 tablets and reduced to a fine
powder. v

Weigh accurately about 0.15g of

ephedrine hcl

add 30 ml anhydrous glacial acetic acid
v

Add 10ml of mercuric acetate

Titrate against with 0.1M perchloric
acid using crystal violet indicator

Violet colour changes to emerald green

Perform the blank determination.
Each Iml of 0.1M perchloric acid is
equivalent to 0.02017g of ephedrine hcl

ASSAY OF SODIUM BEZOATE
Weigh 0.25 f of sodium benzoate

Dissolve in 20 ml of glacial acetic acid.
Warm at 30, C at necessary
Cool and titrate it with 0.1 M perchloric
acid using 0.05 ml of naphthol benzein
as indicator.

v
Carryout the blank titration.
Each1 ml of 0. 01 M perchloric acid is
equivalent to 0.01441 g of sodium
benzoate.

 

72

 

 

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NON AQUEOUS TITRATION — UNIT-II

5 MARKS:

1.Explain the various types of solvents used in Non aqueous Titration?
2.Write in detail about preparation and standardisation of acetous perchloric acid .
3.Explain the principle involved in the Estimation of sodium benzoate
2 MARKS:

1.Define Non Aqueous acid base titration

2. Define titration curve.

3.Define Mixed indicator

4.Define Acidimetry

5.Define Alkalimetry

6.Indicators used in Non-aqueous acid —base titration.

7.Define Amphiprotic solvents with e.g.

8.What are the solvents used in acidimetry & alkalimetry

73

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UNIT-IIT PRECIPITATION TITRATION (OR)  ARGENTOMETRIC TITRATION

SYLLABUS:

Precipitation titrations: Mohr’s method, Volhard’s Method, Modified Volhard’s Method, Fajans
method, estimation of sodium chloride.

It is derived from a Latin word ARGENTUM which means Silver.
Definition of Precipitation Reaction:

A precipitation reaction is a type of chemical reaction in which two soluble salts in aqueous solution
combine and one of the products is an insoluble salt called a precipitate.

Precipitation Titration:

Titration involving precipitation at end of process is called as precipitation titration. most of metallic
halides are titrated by precipitation method.

Solubility:

The molar concentration of solute dissolved in solution at saturated condition at any temperature is
called solubility.

Eg: out of 5 moles of solute suppose 2moles of solute is ionized in a one liter solution at any fixed
temperature .therefore ,here solubility of solute is equal to 2moles.

Solubility product :

The product of molar concentration of ions raised to the power equal to its stoichiometric coefficient
presents in the ionic equation in saturated solution at a fixed tempreature is called solubility product.

Factors affecting the solubility of precipitate:
a) Effect of temperature
b) Effect of solvent
c) Effect of acid

d) pH of the solution

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UNIT-IIT PRECIPITATION TITRATION (OR)  ARGENTOMETRIC TITRATION

A) EFFECT OF TEMPREATURE :
with increased temperature solubility of precipitate increases
B) EFFECT OF SOLVENT :

By adding organic solvents(methyl,ethyl,.)the solubility of most of the organic compounds can be
reduced.

C) EFFECT OF ACID:

the solubilityof the salt of weak acid is affected by the addition of acid hydrogen ion of added acid
combines with the anions of the salt and forms weak acid thereby increasing the solubility of the salt .

D) EFFECT OF pH:
decreases pH increases solubility.
Methods of Precipitation Titration :

According to end point detection method, three main procedures are widely used depending on the type of
application. These are :

a) * Mohr’s Method (Direct titration method)
b) ¢Volhard Method ,Modified volhard’s method(Indirect or back titration)

c) * Fajans Method (Direct titration).

Mohr’s method (Karl Friedrich Mohr)

>» In 1856 Mohr introduced it.

» Mohrs method is used to determine the chloride & bromides .Eg.Nacl,NaBr,Kcl,KBr etc.....

» Todides cannot be determined by Mohrs method,because Iodide will also produce coloured
precipitate with Ag+

It is especially useful for the determination of chloride.
This is direct titration where,

The titrant is: 0.1M AgNQOs.

Analyte is : Cl (eg NaCl)

Indicator : potassium chromate (K2CrO4)

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UNIT-IIT PRECIPITATION TITRATION (OR)  ARGENTOMETRIC TITRATION

Principle:

In this method CI ion solution is directly titrated against AgNO3 using potassium chromate (K2CrO4 )
as the indicator.

Nacl + AgNOQ3 — ------------ > Agcl v + NaNO3
(Sodium chloride) (Silver nitrate) (Silver chloride) (Sodium Nitrate)
(White ppt)

At the end point, when all the chloride ions are removed. The yellow colour of chromate (indicator)
changes into reddish brown due to the following reaction. when the precipitation of cl- is complete,the
first excess of Ag+ reacts with the indicator to precipitate red silver chromate.

KoCrO4 + 2 AgNO3 0 ------------------ > AgeCrO4 +  2KNO3
(Yellow Solution) (Red ppt)

Reaction is carried out in neutral medium for determination of chloride,bromide & not used for Iodide
because of Agl & Ag2CrO4 is same(Reddish brown).

Procedure:

1.Filled burette with 0.1M AgNO3

2.Pipette out 25ml of Nacl solution on 250ml conical flask

3.Added 5 Drops of K2CrO4 as the indicator

4.Titrated with 0.1M AgNO3 Solution till the first colour changed .
5.At the End point formation of brick colour precipitate.
Conditions for Mohr’s method

> Very dilute solution of pot chromate should be used

» The titration should be carried out neutral or slight alkaline condition i.e. pH 6.5 to 9.

>» In acidic condition, hydrogen chromate will be formed and in highly alkaline condition
silver hydroxide(Ksp =2.3 X 10-8)

» Solubility product of silver chromate increase with rise in temperature.

>» Ammonium salt, iodide salts and thiocyanate salt can not be done by Mohr’s method
because In the presence of ammonium salt, the ammonia do have effect of solubility of
silver salt due to increase in pH

» Agl and AgSCN adsorb chromate strongly hence false , indistinct end point results

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UNIT-IIT PRECIPITATION TITRATION (OR)  ARGENTOMETRIC TITRATION

There is always some error in this method because a dilute chromate solution is used due to the
intense colour of the indicator.This will require additional amount of Ag+ for the Ag2CrOa to
form.

Iz AgNO, + NaCl "SS Ag

reddish brown
precipitate

NaCl
K,CrO,

y (white precipitate) 4

   
  

 
 
 

 

 

VOLHARD'S METHOD:
Described by Jacob Volhard, a German chemist in 1874.
This method is also known as the indirect method or back titration method.
So,Two types of titrant is used
Type I titrant is: 0.1M AgNO3.(added in excess to analyte)
Type IT :0.1 M KSCN(Potassium thiocynate ) or
0.1M NH4SCN(Ammonium thiocyanate) filled in burette.
Analyte is : Cl- (eg NaCl)
Other halides like Cl-,I-, & Br- can be determined by volhards method.

Indicator : Ferric alum(Ferric ammonium sulphate)

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UNIT-IIT PRECIPITATION TITRATION (OR)  ARGENTOMETRIC TITRATION

Principle:

STEP 1: Standardization of AgNO3 by Nacl

Nacl = + AgNO3 —---=+=----=- > Agcl + NaNO3
(Sodium chloride) (Silver nitrate) (Silver chloride) (Sodium Nitrate)
(White ppt)
STEP 2:
1)Nacl+ AgNQO3 (Excess) -------------- > Agcl + NaNO3 +AgNOs ( Excess)
(20 ml)
NL
2) AgNO3 + = ~=KSCN_ --------------- > AgSCN +  KNO3
(OR)
AgNO3 +  NHASCN ----------------- >  AgSCN + NH4NOs
3)Fe* 4 3NEUSCN eee +5 Fe(SCN3 + — 3NH4t
(reddish colour)
Procedure:

1.Take Nacl standard solution in a conical flask & add 2 ml of chromate (Indicator) & Titrate
with AgNO3 solution.

2.At the endpoint reddish brown / Brick red colour precipitate will form.

3.Take a sample solution (NaCl ) & add excess solution of AgNO3 & 2 drops of Ferric ammonium
sulphate (Indicator)

4.Titrate the above solution by using standard solution of KSCN (OR) NH4SCN

5.At the end point Reddish colour precipitate of Fe(SCN) will occur due to completion of
reaction. Calculate the amount of Nacl

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UNIT-IIT PRECIPITATION TITRATION (OR)  ARGENTOMETRIC TITRATION

   
  
  
  

erne alum,

Volhard’s methoa:AgNO; + NH,SCN '

.
_.2 MHNO

      

AgNO,
Fe alum, HNO,

v (white precipitate) Ag
ae . z < ‘Ghd M4 \
Fe(SCN), (reddish yellow colous’solifi >

 

 

ADVANTAGES OF VOLHARD’S METHOD:

» This method is useful where the titrations have to be performed at low pH.

» The strong acidic environment give advantage for halide analysis because ions like
carbonate, oxalate and arsenate do not interfere.

» Give accurate results due to back titration.

LIMITATIONS OF VOLHARD’S METHOD:

> Can not be used where the solution has to be neutral
> Time consuming.
> Sometimes adsorption of Ag* may give false end point.

 

Direct titration of halide with silver nitrate Indirect titration or back titration

Indicator— Pot Chromate Indicator Ferric ammonium sulphate
End point- red precipitate of silver End point- red soluble complex of ferric
chromate thiocyanate

Condition for titration : Neutral to alkaline Condition for titration : Acidic solution
(pH 6.5 — 9.0)

Titration of lodide and cyanate is not Can be used for determination of chloride,
possible bromide and iodide
As solubility of silver chromate increases As the color of ferric thiocynate complex
with rising temp, titration are carried out fades above 25°C, the titration are carried
at RT below 20°C

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UNIT-IIT PRECIPITATION TITRATION (OR)  ARGENTOMETRIC TITRATION

Modified volhard’s method

* Especially NaCl or KC] are determined.

Modified Vothard’s method: Back _ titration
analysis. Excess silver nitrate is reacted with NaCl. Then unreacted
titrated with NH4SCN using ferric alum (indicator) in acidic medium
Excess AgNO, + NaCIl—*AgCl + NaNO, + unreacted Ag NO

Linranted AgND, + NHLSON Sâ„¢88* AgSCN| + NHNO
" 2MHNO, ~

NH4SCN + AgCi -- AgSCN)|. This unwanted
reaction is prevented by

1. Addition of Nitrobenzene or dibutyl! phthalate:
it form film at precipitate surface. This prevent
reaction between NaSCN & AgCl.

. Filteration of precipitate.

2M HNO, stop hydrolysis of ferric alum
{H4aSCN + Unreacted AgNO, — AgSCN |
‘hite precipitate is formed before end point
14SCN + Ferric alum — Fe(SCN),
eddish yellow solution is formed at
dd] point

   
  
 
 
 
 
 
 
 
 
 
       
     

 

 
 
  
  
  

(white precipitate) .
Fe(SCN), (reddish vel

Nitrobenze

  

Fajan’s method (Kazimierz Fajans)
* In 1923-24 Fajan introduced the method
* It is based on the mechanism of Adsorption.
It is used to determine chlorides,bromides,Iodides.
Titrant : AgNOs
Analyte : Nacl
Indicator : Fluorescein

Nacl + AgNQ3  ---------- > Agel + NaNO3

White precipitate is formed before end point
AgNO; + Fluoresein -------------- > AgFluoresein

Pink layer on precipitate is formed after endpoint.

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UNIT-IIT PRECIPITATION TITRATION (OR)  ARGENTOMETRIC TITRATION

Methodology:

1.Take 10ml sample of Nacl (Conical flask)

2.Add few drops of Fluoresin indicator

3.Titrate the above mixture solution by using AgNo3 solution

4.At the end point Pink colour precipitate will occur on the surface of Agcl precipitate

5.At the end point reading is taken from the burette and calculation is done accordingly.

Mechanism:

-| Adsorption indicator is chemical
determine end point by
adsorption on precipitate. Eg:

dichlorofiuoresein.
NaCl
‘Juoresei

Before end point

Ge

Amaia mary we

' BS Na’)

      

AgNO

Before the end point :

Nacl + AgNO3  _—_ -------- > Agcl + NaNO3
Agcl is formed.Cl form 1° primary layer.

1° Layer attract N a’ to form 2° Layer.

Na’ & Cl form white layer on Agcl before endpoint

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UNIT-IIT PRECIPITATION TITRATION (OR)  ARGENTOMETRIC TITRATION

After the end point :

chloride is finished.Ag+ form 1° Layer

F is preferentially attracted by 1° layer.

Ag* & F form pink layer on Agcl

Adsorption indicator

INDICATOR COLOUR CHANGE (free APPLICATIONS

to adsorbed)
Fluorescein | Yellow-green to pink All halides, pH 7-10
Eosin | Pink to red-violet | Sample must pot contain CI
pH 1
Diiododimethyi fluorescein Orange to blue | T only, pH 4-7

Dichloroflucrescein Yellow-green to red CT and Br’, pH 4-7

ESTIMATION OF SODIUM CHLORIDE:

Estimation of sodium chloride

Weigh accurately about 0.1 g NaCl and
dissolve in 50 mi of water in a glass-stoppered
flask. Add 50.0 mi of 0.1 M silver nitrate, 5 mi of
2 M nitric acid and 2 mi of dibutyl phthalate,
shake well.

   
  
 
 
 
  
 
 
    

Titrate with 0.1 M ammonium thiocyanate using
2 mi of ferric ammonium sulphate solution as
indicator, until the colour becomes reddish
yellow

 

  

mi of 0.1 M silver nitrate is

Gi white precipitate)
quivalent to 0.005844 g of NaCi

e({SCN), (reddish ye
Dibuty! ph thal

  

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UNIT-IIT PRECIPITATION TITRATION (OR)  ARGENTOMETRIC TITRATION

10 MARKS:

1. What is Argentimetric titration? Give a detailed account of different methods of
argentimetric titration.

5 MARKS:
1. Explain with reactions the principle involved in Mohr’s mehod.
2. Ilustrate with reaction and examples,the principle involved in volhard’s Method.

3. Write notes on Modified Volhard’s method.

4. Write a note on Fajan’s Method.
2 MARKS:
1. Define precipitation titration

2. Define solubility & solubility product

3. Write the classification of precipitation titrations.

4. Give factors affecting the precipitation titrations.

5. Differentiate between Mohr’s and Volhard’s method.

6. What are the indicators used in Fajans method.

PAs fs 2s fs 2s 2s ops fe fe fs fe fe fs 2s 2s 2s ois 2s 2s ofc fe of 2s fs ole fe fs 2s as os 2s 2s of of 2s 2s of fe fe fe of fe fs ois fs 2s os 2s 2s 2s of fe ofc of fe fe fs ois fe fs ois 2s 2s ofc 2s 2s 2s oe oe 2 2

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UNIT - UI COMPLEXOMETRIC TITRATIONS

DEFINITION:

» Itis the type of volumetric analysis involving in the formation of complexes.

» The reaction in which simple metal ion is converted into complex ion by the addition of
the reagent.

>» Complexometric titrations are particularly useful for the determination of a mixture of
different metal ions.

PRINCIPLE:

In Complexometric titrations,the metal ions are titrated with a complexing or a chelating
agent(Ligand).This method involves transforming a simple ion ino a complex ion and
determining the equivalence point using metal indicators .

This method is also known as CHELOMETRIC TITRATION, CHELOMETRY,
CHELOTOMETRY TITRATION, EDTA (Ethylene Diamine Tetra acetic acid )TITRATION.

Metal ion indicators

 

 

 

 

 

 

 

 

 

Metal ion + Chilon 9 £2 £22 weewnnnnnnnnne--=-- > Chelate
pM Indicators
(Analyte,cation) Complexing agent Complex
Chelating agent Metal coordination cmpd
Ligand Metal complex
Sequestering agent Chelate compound
Eg:
Ca2t Indicator EDTA Ca 2+
Mg 2+ (EBT Or Mordant Black T Or |--------------------- > Mg 2+ + EDTA| + EBT
(Sample) Solochrome black T |
RED 84 COMPLEX(Colourless) Blue

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UNIT - UI COMPLEXOMETRIC TITRATIONS

IMPORTANT TERMS

COMPLEX:

A metal ion combines with a molecule which can donate electron.
CHELATES:

If the combining molecule contain two or more groups that donate electrons, this complex is
called chelate.

LIGAND :
A species which can donate lone pair of electrons. It bound to the central metal ion.

SEQUESTERING AGENT:

Sequestering agents are the chelating agents forming water soluble complexes with bi- or
polyvalent metal ions.

CHELATING AGENT:

Ligands with more than one electron donating group are called as chelaing agents.The ring
Structure by the ligand group with the same metal ion is called as chelating agents. The
complexing agent itself is called as chelating agent. vExample: EDTA

TYPES OF LIGANDS :
1.Monodentate Ligands:

>» These are the ligands which can donate only one pair of electrons to the metal atom
through coordinate bond

Only one ligating atom

Also known as Unidentate Ligands

Neutral Molecules

Negatively charged

Postively charged

VVVV WV

Eg. [Co (NH3)6 ]** —, [Fe (H»O)¢]�*

NH3 2+

HN ey J oo NH,
H.Nw l “SF NH;
H3N
NH3 Complexing with cupric ions.

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UNIT - UI COMPLEXOMETRIC TITRATIONS

2.Bidentate Ligands:
Bidentate Ligands which can donate two lone pair of electrons towards the metal atom

Eg: HaN-CH2-CH2-NH)2 (Ethylenediamine) en

CH,- CH,

   

3.Multidentate :
These have several points of attachments (or) When more than 2 or 3 sites are present.

Eg: EDTA ,Which is a hexadentate ligand (six points of attachment)

Fs. ot. proe�
ee ee
— ae te, cote Na
â„¢~ ~~
— x
o—so
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UNIT - UI COMPLEXOMETRIC TITRATIONS

WERNERS CO-ORDINATION NUMBER
It is defined as a metal ion complex, the total number of bonds of metal atom with ligand.
Eg: Fe[H20]« * - 6 co-ordination number.
The co-ordination number depends on the following:
Steric factors.
Nature of ligands.
No. of pairs of electrons with metals.
Stereo-chemical environment of the metal ion.
TITRANT IN COMPLEXOMETRY
A large number of inorganic and organic titrants are used in this titration.
Eg: poly amino carboxylic acid
imino di acetic acid
nitrile tri acetic acid
Ethylene diamine tetra acetic acid EDTA — these are widely used in a form of disodium salt
DISODIUM EDTA

This titrant is used for the determination of all metal ions

It is more water soluble , non hygroscopic and very stable.

It has higher molecular weight(372.24).

0.1M EDTA are prepared by 37.2g of EDTA dissolving in litre of solution.
It chelate with di, tri, tetravalent cations to form complex.

VVVV Vv

NaOCOCH, CH,COONa

NN a
NCH CHyN
a SN CH,COOH

HOCOCH2

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UNIT - UI COMPLEXOMETRIC TITRATIONS

REASONS FOR THE VERSATILITY OF DISODIUM EDTA
>» It forms soluble stoichiometric 1:1 complex with metal ions.

On the basis of stability constants and control of pH of the solution, the metal ion in EDTA
titration are divided into 3 types:

I — metal ion titrated in basic condition (pH- 8-11)

Eg: magnesium, calcium and barium.

II — metal ion titrated in acidic to neutral condition (pH -4-7)
Eg: manganese, iron, copper, zinc.

III — metal ion titrated in acidic condition(pH -1-4)

Eg: mercury, bismuth, cobalt, titanium.

TYPES OF COMPLEXOMETRIC TITRATIONS

> Direct titration

> Back titration

> Replacement or substitution titration
> Alkalimetric titration

Direct titration :

©

» In this type of titration take a metal ion solution in conical flask and maintain necessary
pH by adding buffer solution(pH =10 with NH4Cl + NH1OH)

Then titrate with standard EDTA Solution in the presence of suitable indicator .

At the endpoint fast & big change obtain in the conc.of the metal ion.

eo

*

eo

*

eo

*

Thus indicator gives colour change.
During the titration, if hydroxide of metal ion precipitated,the solution of citrate,tartret or

eo

*

triethanol amine is added to prevent precipitation of metal hydroxide.
¢ Eg: Zn** .Mg* can be titrated by direct titration method.

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UNIT - UI COMPLEXOMETRIC TITRATIONS

1. Direct Titration

   

 

 

 

 

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UNIT - UI COMPLEXOMETRIC TITRATIONS

Back titration:

“* Back titration is used when
(i) Reaction is very slow as well

(ii) Indicators are not available.

(111) Sometimes metal ions is more stable than M- EDTA complex,so cannot be titrated by
direct titration method.

“+ In such cases an excess of standard EDTA Solution is added & maintain necessary pH
by adding buffer solution.

“* Excess of the EDTA is back titrated with a standard metal ion solution like Magnesium
sulphate / Magnesium chloride or Zinc sulphate / Zinc chloride solution in the presence
of suitable indicator.

“+ By substracting volume of EDTA & unreact volume of EDTA,the volume of used

EDTA is calculated.

This type of titration is called back titration.

Eg. Co*?, Al** Cu Ni� can be titrated by back titration method.

eo

*

eo

*

2. Back Titration

3 Standard ZnSO, or MgSO, solution =
j

 

 

 

Co-EDTA + EDTA

. indicator added excess EDTA is
<x titrated back with —

 

 

 

HI

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UNIT - UI COMPLEXOMETRIC TITRATIONS

2. Back Titration
7Example
M (e.g.Co) + EDTA( excess ) (say 100mL added)
| torms

Co-EDTA (60 mL) + EDTA(40 mL)

titrated with ZnSO4 gives reading at 60 mi
Therefore, Consumed amount = Total added — Unused amount
= 100 — 40

2 60 mi

Replacement titration or substitution Titration :

.¢,
“

eo

*

eo

*

Substitution or replacement titration may be used...,
(i)For meal ions that do not react with a metal indicator.

(ii) For Metal ions which form EDTA complexes that are more stable than those of other
metals such as Mg * or Zn*â„¢

Suppose concentration of M*" ion would be measure in the following way

For this solution of complex of Mg **, or Zn * with EDTA is added to Mâ„¢ meal ion
solution,therefore following reaction takes place

Mn� +MgEDTA® --------------- > MnEDTA� + Mg�

When solution of complex of Mg - EDTA Or Zn — EDTA is added to the solution of M*"
metal ion,equivalent amount of Mg * ions will be free,which will titrated by standard
EDTA Solution in the presence of suitable indicator by direct titration method.This
titration is called replacement titration.

Eg: For the estimation of Ba® ion,Zn * ion replaced from Zn —EDTA Similarly for
Ca** ion,Mg * ion, replaced from Mg-EDTA Complex.

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UNIT - UI COMPLEXOMETRIC TITRATIONS

3. Replacement Titration

 

 

 

 

 

 

 

 

 

 

 

 

-
indicator
LJ Ca? + Mg-EDTA > Ca-EDTA +] Mg’ 1+ Mg-EDTA
<4 (20 motes} [20 moles] (Remaining)
wr
f-\

Alkalimetric Titration :
“* When EDTA Solution is added to the metal ion solution,the metal ion form complex

with EDTA & Equivalent amount of H + Ions will be obtained which will represent by

following way:

+ Y -2
Mâ„¢ +H, ~ -------------

+
Obtained H_ ion is titrated with standard NaOH Solution in the presence of suitable indicator.This

method is called alkalimetric titration.The metal ion solution should be neutral,whose alkalimetric

titration is carried.

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UNIT - UI COMPLEXOMETRIC TITRATIONS

MASKING AGENT

5 When the solution contains a mixture of two or more metal ions

y EDTA donot react with any one particular ion.But it react with every one metal ion present in
the solution to form complexes.

5  Therfore, the estimation of any one ion,Some reagent is added to the mixture which form
stable complex with other ions it means they are inactive.

y This is called as Masking and reagent is to be added for masksing its called as Masking

agent.
DEFINITION :

vy. Masking may be defined as the process in which a substance without the physical sepration
of it or its reaction products is so transformed that it does not participate in a reaction.

vy In simple words its reaction is Masked.

For Example :

. . +2 +2
y Suppose solution has two ions,Pb  & Zn

+2 +2
y» HerePb & Zn are found by titrating with standard EDTA solution by masking —

demasking Method.

> Excess of KCN is added in the mixture of Pb * & Zn* to mask Zn� as
[ Zn (CN)4]?

But Pb*® donot form cyanide complex , it means Pb� free in the solution.
Therefore pb+2 can be titrated with EDTA Solution at that time Zn +2 do not interfere.

Cyanide ion form stable complex with Cd * , Cu? ,Hg **,Co�,Ni * .Zn � metal
ion,while it do not form stable complex with Be ** Mg ** Ba *,Sr **,Pb *,Caâ„¢.

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UNIT - UI COMPLEXOMETRIC TITRATIONS

EXAMPLES OF MASKING AGENT

AMMONIUM FLUORIDE - Fluride = — mask aluminium, iron, titanium.

>

y» ASCORBIC ACID - It will mask iron, copper

> DIMERCAPROL(B.A.L) - It will mask antimony, mercury, zinc,tin,lead
> POTASSIUM CYANIDE — iron, copper, zinc, cadmium and cobalt,silver
y POTASSIUM IODIDE — Mercury

> TIRON — Aluminium, iron

CONDITIONS IN MASKING TECHNIQUES

Proper selection of a masking reagent

Proper selection of a principal reagent

Proper control of pH

Quantity of masking and principal reagent to be used.

Effect of oxidation state on stabilities of complex formed

Vv Vv VV WV WV

Solvent used and use of selective metal indicators
DEMASKING AGENT

vy This is process in which masked element or compound is released from its masked form and
regain its activity to enter into reaction

vy Eg: formaldehyde , chloralhydrate ,acetic acid

+2 +2
Demasking of cyanide complex of Zn &Cd _— can be carried out with the help of mixture of

formaldehyde & acetic acid reaction is given below:
2 + +2
[Zn (CN)4] + 4H  +4HCHO -------- > 2n +4HO -CH2 -CN

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UNIT - UI COMPLEXOMETRIC TITRATIONS

+2
In this way liberated Zn ion can be titrated by EDTA solution.Similarly mixture having many ions

can be titrated by above masking & demaskind method.

Example:

>

+2 +2 +2
Titration of mixtureofMg ,Zn ,Cu _— can be carried out with EDTA Solution by

following way.

+2 +2 +2
Take 25 ml of mixtureofMg ,Zn ,Cu ions & then add excess of specific volume of
standard EDTA Solution & remaining EDTA Solution can be titrated with standard ZnSO4
Solution.
Then with the help of them volume of used EDTA Will be measured.

42 42 42
Repeated take 25 ml of mixtureofMg ,Cu_ ,Zn _ ions,then add excess of masking agent
KCN Solution.

+2 42
ThusZn & Cu

ions are masked as [ Zn (CN yy & [Cu (CN yy Complex ions
respectively & Mg " will be free.

Then in the above solution ,mixture of formaldehyde and acetic acid.

Thus Zn * Can be damask from their cyanide complex ion and free Zn can be titrated by

2
standard EDTA Solution and amount of Zn * can be found.

+2
The amount of Cu is found by different between above both titration.

METHODS USED FOR DEMASKING:

>
>

Decomposition of the masking reagent

Replacement of the masked ion in a complex by another ion with which the masking agent
forms a stronger complex.

By change of pH to alter the stability of a complex.

By changing the oxidation state of the completed ion.

By volatalization of one of the components of the masked system

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UNIT - UI COMPLEXOMETRIC TITRATIONS

METAL ION INDICATOR (pM INDICATOR)

vy These are organic compounds which form coloured complex ion with metal ion.

vy The quality of a good indicator are sharpness of colour change at the endpoint.
GENERAL PROPERTIES:

The colour reaction must be the metal — edetate complex.
The colour reaction should be specific or selective.

The end point should be sharp and rapid.

VV V WV

The indicator must be very sensitive to metal ions. So the colour change occur at the end
point is easier.

The above requirements must be fulfilled within the pH range .

Vv

y Therefore, the metal ion indicator are not only pM indicator but also pH indicators.

CLASSIFICATION OF PM INDICATOR :

HYDROXYLAZO COMPOUNDS

 

* Mordant black T
* Solochrome dark — blue(calcon)

PHENOLIC COMPOUND AND HYDROXYL SUBSTITUTED TRIPHENYL METHANE
COMPOUND

+ Xylenol orange
* Catechol violet
* Methyl thymol blue

COMPOUND CONTAINING AN AMINO METHYL DICORBOXY METHYL GROUP

 

 

* Alizarin fluorine blue
* Sodium alizarin sulphonate

MISCELLANEOUS

 

* Diphenyl carbazone
* Variamine blue, murexide

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UNIT - UI COMPLEXOMETRIC TITRATIONS

pM INDICATOR ( MORDANT BLACK IT )

(Erichrome Black T , Solochrome Black )

Chemically it is 1-(1-hydroxy-2-naphthlazo)-5-nitro-2-naphthol-4-sulphonate.
Any titration were the pH between 7 and 10.

At pH —7 to 10 — it gives blue colour.

At pH — 10 — gives red —purple colour.

pH. below 6.3 — red colour

pH above 11.5 — red colour.

Vv Vv Vv VW WV WV WV

Magnesium, calcium , cadmium , zinc.Manganese, lead and mercury may be titrated Using

this indicator.
H Q.
CK
SNL)
"  &)
NO>

SOLOCHROME DARK - BLUE

y This is also referred to as Erichrome blue black
y» Chemically it is sodium-1-(2-hydroxy-1 naphthylazo)2 naphthol-4- sulphonate.

y Itis brownish black powder with violet sheen.

PREPARATION:

y 0.2g dye +50ml methanol. It gives purple red colour with calcium ions in alkaline solution.
y The free indicator is blue in colour in EDTA Solution.
y tis used to assay calcium chloride, calcium carbonate ,calcium gluconate.

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UNIT - Il COMPLEXOMETRIC TITRATIONS
OH HQ 00
\—N=N Sona

MUREXIDE (AMMONIUM PURPURATE)

VVVVVVV VV

>

This is first metal indicator used in complexometric titration.

It has various colours at different pH.

At pH- upto 9 — reddish violet.

At pH- 9 to 11 — violet.

At pH — above! 1 — blue violet.

This indicator is mainly used in titration of calcium at pH — 11.

The colour change at the endpoint is form red to blue violet

Aqueous solutions of murexide are unstable & must be prepared each day
The indicator solution may be prepared by suspending 0.5g of the powdered indicator in
water,shakingly thoroughly & allowing the undissolved portion to settle.
The saturated supernatant liquid is used for titrations.

XYLENOL ORANGE

VVVV VV

Vv

It is an acid base indicator.

In acid solution — lemon yellow

In alkaline solution — red .

The indicator solution is prepared by dissolving 0.1gm in 100ml of water.

Its pH range vary from 4-7

Mostly metal complex are red . Hence it restricted to titrating metal whose EDTA
complex stable in acid solution.

It gives violet colour with mercury, lead, zinc in alkaline solution.

If these metal ions are absent, the solution remains yellow because of excess of EDTA
solution.

It is used in the estimation of aluminium hydroxide gel,aluminium sulphate etc...,

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UNIT - UI COMPLEXOMETRIC TITRATIONS

CATECHOL VIOLET:

It forms highly coloured complex with wide range of metals.

0.1% Solution in water is employed as indicator

Catechol violet has advantage that its very stable in aqueous solution.
Complex with metals are blue in alkaline solution and also acidic solution.
The ph range is 4-7.

It is used to estimate Mg,Mn,Co,Zn,Ca & Cd ions.

VVVV VV

METHYL THYMOL BLUE:

> It will function in both acid & alkaline media;pH 0-12
> When indicator complex with metal it produce blue & absence of metal it is grey colour.
> Methyl thymol blue used as colorimetric reagent for Ti,Al Fe,Hg,Mg.

ESTIMATION OF MAGNESIUM SULPHATE:

Principle:

It is Complexometric titration in which magnesium sulphate is titrated with disodium EDTA
using Mordant black IT indicator until blue colour is obtained.

Reaction:
Mg� + EDTA (2 cseeeeeceeseeee ene > Mg-EDTA
Magnesium ion Disodium Edeate Magnesium-disodium edetate

PREPARATION OF 0.05M DISODIUM EDTA:
> Dissolve 18.6g of disodium edetate in sufficient water to produce 1000ml.
STANDARDIZATION OF 0.05M DISODIUM EDTA:

0.8 of zinc dissolve by gentle warming

Add 12ml of dil.HCl] and 0.1ml of bromine water

Boil to remove excess bromine, cool and add 200m] water

Pipette out 20ml1 and neutralize with 2M sodium hydroxide

Dilute to 150m] with water

Add ammonia buffer to maintain pH-10.add 5ml excess

Titrated with 0.05M disodium edentate using mordant black II indicator until the solution turns
blue.

Each Im] of 0.05M DISODIUM EDTA is equivalent to 0.000654¢ of zinc.

VVVVV VV

Vv

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UNIT - UI COMPLEXOMETRIC TITRATIONS

ASSAY OF MAGNESIUM SULPHATE

> Weigh 0.3¢ of anhydrous magnesium sulphate

> Dissolve in 50ml of water

> Add 10ml of ammonia buffer to maintain pH 10

> Titrate with 0.0S5M DISODIUM EDTA using mordant black II mixture

» Appearance of blue colour.

> Each ml of 0.05M DISODIUM EDTA is equivalent to 0.006022 of MgSO4

woeneenenennn= > 0.3g Magnesium sulphate + 50 ml water + 10ml ammonia —
ammonium chloride + 2 drops of Indicator mordant black IT

 

 

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UNIT - UI COMPLEXOMETRIC TITRATIONS

ESTIMATION OF CALCIUM GLUCONATE:

Principle :

This is a replacement titration magnesium forms complex with mordant black II mixture indicator which
forms first colour.

Mg ** + Teen enn n nnn nnn > Mg-In
Magnesium ion Indicator Magnesium indicator complex
Ca * + EDTA ( weeeeeeeesenneennneeee ee > CaEDTA
Calcium ion Calcium disodium edetate complex
Mg-In + EDTA (wane n en nnnn nnn nn nnn e ne nennne > Mg-EDTA + In(indicator)
> Weigh 0.5¢ of calcium gluconate
> Dissolve in 50ml of warm water
> Cool and add 5ml of 0.05M magnesium sulphate,
> Add 10ml of ammonia — ammonium chloride solution or ammonium buffer solution.
>» Titrate against EDTA Using mordant black II mixture till the colour changes from pink to blue
> Each ml of 0.05M EDTA = 0.02242¢ of calcium gluconate.

NOTE: from the volume of 0.05M disodium EDTA required to subtract the volume of the magnesium
sulphate solution.

is wan nen enna ne nnnennne n= >EDTA

ween nen en nance nen ne >0.5g Calcium gluconate + 50 ml warm water +5 ml
of 0.05M Magnesium sulphate + 10ml ammonia —ammonium chloride
{ + 2 drops of Indicator mordant black IT

\
@° *@ J

 

 

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UNIT - UI COMPLEXOMETRIC TITRATIONS

IMPORTANT QUESTIONS:

10 MARKS:

1.Explain in detail about different types of complexometric titrations with examples.

2.What are the different indicators used in complexometric titrations ? (or)
Write a note on pM indicators and its classification (or) Metal ion indicator

3.Explain in detail about Masking and Demasking agents with examples.

S5MARKS:

1.How will you estimate Calcium gluconate ?

2.How will you estimate Magnesium sulphate ?

3.What are ligands & explain its types?

2 MARKS:

1.What is Complexometric titration?

2.What are ligands

3.What is chelate

4.What are the different types of Complexometric titrations

5.what is pM indicaor or metal ion indicator?give examples

6.Define Masking agent with example

7. Define DeMasking agent with example

8.Chelating agents

9.Sequestering agents

10.Indicators used in Complexometric titrations

11. Werners co-ordination number

12.Back titration

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UNIT - Oi GRAVIMETRIC ANALYSIS

SYLLABUS:

Principle and steps involved in gravimetric analysis. Purity of the precipitate:
CO-precipitation and post precipitation, Estimation of Barium sulphate.
PRINCIPLE:
>» Itis process to isolating and weighing an pure compound from the element.
Bacle + H2SQ4 2 wwe > BaSO4 + 2HCL
(Analyte) (Precipitating agent) (Precipitate)
The separation of the element or the compound by following ways:
1.Precipitation methods
2.Volatilisation - ignition or drying.
3.Electro gravimetry.
4.Thermogravimeric
PRECIPITATION METHODS

Â¥ Weighed quality of sample dissolved in suitable solvent to solution form.
Â¥ Precipitated by precipitation agent.
¥ Filter -dried — weighed — calculate the % of content.

VOLATILISATION OR EVOLUTION METHOD:

To remove the volatile substance. It is carried out by:
1. By simple ignition in air
2. By treating with chemical agent to get volatile substance.
3. By treating with chemical agent to get non substance.
ELECTRO GRAVIMETRY

Â¥ The substance is deposited electrolyt ically to suitable electrode then filter mostly it used
to estimate.

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THERMOGRAVIMETRY

Â¥ To keep both sample and returns them apply thermal power. The measure what are the
changes occuring in both sample and reference.

VARIOUS STEPS INVOLVED IN GRAVIMETRIC ANALYSIS :

 

1.Sampling
2.Precipitation
3.Digestion
4.Filteration
5.Washing
6.Drying

7 Igniting

8. Weighing
9.Calculation
1.SAMPLING:

Â¥ Sample should be homogeneous

Â¥ Sample should be in powder form

Â¥ Cost of test, Value of product,end use of products,accuracy of test methods and nature of
materials used are considered in this.

2.PRECIPITATION:

Â¥ Precipitation are usually made by using beakers.

Â¥ Beakers is covered by clock glass.

Â¥ To add precipitating reagent (by using pipette or burette) by slowly with sufficient
stirring.

To avoid the splashing by adding precipitating at moduate speed.

The stirring rod should not touch the surface or walls of the beaker.

Then allow the percipitate settle overnight or by heating the precipitate.

To reduce the coarseness of the precipitate.

Filter

Collect the precipitate

SSK KKK

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Example: BaCl, + H,SO, > BaSO, + 2HCI

Beaker containing
precipitan!

Glass rod

Beaker
containing

precipitate s*Sbe ee sai a

Precipitation

3.DIGESTION :

‘Digestion decreases colloidal particles and increase
| e size of precipitate.

  

| sy 4 & cooled sowly

| 1: Liquid is heated and cooled. On cooling or ;

| adsorb on nuclei of itate: Kept for 12-24 hours

FE Liquid is kept for 12- 24 hours. Digestion |. coricles

 

4.FILTERATION & 5. WASHING

4 Filteration separate precipitate from mother liquor. _ Beaker containing
Whatman’s filter paper is kept in funnel.

  

Stem of funnel touch side of beaker to shes.
Filter paper is wetted with water ' tant is.
decanted on the side of glass rod

5 Washing remove impurities. Washing solution is
ar electrolyte solution containing an ion common to

precipitate
*Funnel is filled with washing solution
solution collected in beaker contain

   
    

“Test for complete washing: Filtrate coming from |.
funnel is tested for impurity: Absence indicates

Washing of precipitat

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precipitate. Funnel containing precipitate is dried containing
1. In hot air oven or precipitate
2. On metallic cone kept on tripod stand. lay pipe

6. Drying remove solvent and volatile impurity | rucible.. filter pape
triangle

 

~~

7. Ignition change precipitate into stoichiometric form

 

(has fixed composition). at
Method A: Precipitate with filter paper is taken in crucible iti

4 gnitio
Heated gently on clay triangle pipe. =
When filter paper burns off, heated at 8 Weighing = x grams
required temperature. . .
Heating, cooling and weighing is done untill 9 Calculation: BaSO, —- Ba�

weight of crucible is constant

Method 8B. Filter paper with Filter paper is burnt

directly into ash using tong 233 g of BaSO, has 137 g of Ba**
Ash is collected in crucible. 1 g of BaSO, has 137 / 233 g of Ba**
Heating, cooling and weighing is done untill
weight of crucible is constant x g of BaSO, has x137 / 233 g of Ba**

1 mole = 233 g 1379

Purity of the precipitate:
CO-precipitation and post precipitation,
CO-PRECIPITATION:

>» When a precipitate separate from solution,it is not always perfectly pure.

> It may contain some amount of impurities depend upon nature of precipitate and
condition of precipitat

» Contamination of precipitate by substance which are normally soluble in mother liquior
called co-precipitation

TYPES OF CO-PRECIPITATION

» Surface Adsorption

> Mixed crystal formation
» Occulsion

>» Mechanical Entrapment

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Mechanism of
4. Adsorption: when impurity has jon common to precipitate
impurity gets adsorbed on precipitate

Gg: (impurity) BaCl, is coprecipitated with BaSO,
** forms primary layer and Ct form secondary layer

2. Mixed crystal formation: when impurity has same size
and charge as ion present in precipitate, then it replace ion of
precipitate

Impurity
Eg: when BaSO, is precipitated in solution having PbSO,,

then Pb replaces barium due to same charge and size.
thus the precipitate contains BaSO, and PbSO, -

 

 

 
   
 
  

3. Occlusion / solid solution: In very °
concentrated solution, impurity is not able to |@ [email protected]

leave the precipitate nucleus and is trapped oa
precipitate: When both nucleys afe very

ty prpcipitate
e-60-

     
     
   

    
   

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POST PRECIPITATION
“Post precipitation is the precipitation of impurity
after some time of the sample precipitation�

Post precipitation increases with increase in time.

   

Mechanism: S

when Mg oxalate is present in Ca oxalate
solution.

Oxalate ion forms primary layer and Mg ions form
secondary layer

Thus Mg oxalate is post precipitated on calcium
oxalate.

Prevention of post precipitation:
*Precipitate is filtered quickly
*Digestion

*Reprecipitation , ——=>
*Glass piece is added to act as nucleus for impurity. cyjece of time on post precipitation

 

post precipiation —»

Estimation of Barium sulphate.

 

In Gravimetric analysis,the amount of sulphate is estimated quanitaively as barium
sulphate(BaSO4) .In this assay,dilute solution of barium chloride is gradually
added to a hot acidic solution of sulphate.This solution is acidified with the hot
Hcl acid solution.

Ba 2+ + SO4 Q- wenn nnnennn nanan > BaSO4

The barium sulphate precipitate is filtered, washed with water,ignited at red heat &
weighed.

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PROCEDURE:

1. A Procelain crucible is heated to redness and placed in a dessicator to cool.

2. Accurately weighed 0.2 gm of barium chloride is dissolved in 100ml of
water.

3. The solution is boiled and a slight excess of hot 0.5M sulphuric acid solution
is added slowly in it with continuous stirring.on a steam bath,the solution is
digested until the precipitate has settled.

4. Few drops of 0.5M Sulphuric acid are added to the supernatant that confirms
the completion of precipitate

5. For filtration a whatman (NO.4) filter paper is positioned on a funnel.

6. The precipitate is transferred to the filter paper using a jet of water from the
wash bottle and a policeman if required.

7. The precipitate is washed a number of times using small portions of hot
water.washing is continued till about 5 ml of the filtrate shows no turbidity
with one or two drops of dilute AgNO3 Solution.

8. The cooled crucible is weighed and filter paper is transferred to the crucible
with the precipitate

9. The paper is kept for drying with the loosely covered crucible over a low
flame.Heat is increased slowly till the paper chars and the volatile matter is
expelled.The whole process should be performed carefully to avoid the
bursting of paper into flame.

10.After the completion of charring,temperature,is increased till the crucible
becomes dull red in colour,and burn off the carbon with free acess of air.

11.The crucible is kept for 10 minutes at red heat,after the precipitate turns
white.

12.The crucible is placed in desicattor for cooling and weighing is done.

13.The process of heating and cooling is replaced coninously till a constant
weight is obtained.

14.The percentage of barium is calculated in the sample.

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5 MARKS :

1.Discuss various steps involved in gravimetric analysis
2.Write a note on Co-precipitation & Post precipitation (OR)
Write a note on Purity of the precipitate
3.Estimation of Barium sulphate
2 Marks :
1.Define Gravimetric analysis or principle involved in Gravimetric analysis
2.Define Co-precipitation
3. Define Post precipitation
4.Type of Co-precipitation

5. Types of Gravimetric analysis

oi oie 2s 2s 2k 2k 2s 2s 2k 26 2k 2s 2s 2k 2s 246 2k 2s 2f¢ 2k 2s 2s 2k os 2s 2s 2s os 2s 2s 2s 2s 2s os 26 2s os oie 2s os ofc 2 os ofc 2k 2s 2k kk

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UNIT-IT =DIAZOTIZATION TITRATION

DEFINITION:

» The diazotization titration is the conversion of the primary aromatic amine into a diazonium
compound.

» Inthis method,the primary aromatic amine is reacted with sodium nitrite in acidic medium to
form a diazonium salt.

» This method is first used in the determination of dyes.

PRINCIPLE:

Primary aromatic amine is reacted with sodium nitrite in the presence of acid such as Hydrochlroic acid
to form a diazonium salt.

STEP 1: NaNO2 + HCL 0 weeeeeneeeee = > HONO + NaCl
(Sodium Nitrite) | (Hydrochloric acid) (Nitrous acid) (Sodium chloride)
STEP 2 : CeHs5NH2 + HONO + HCL  —— wnr-e--2---------- > CoHsN=NCl + 2H20
(Primary aromatic amine) (Nitrous acid) (Hydrochloric acid) (Diazonium salt)
OR
CoHsNH2 + NaNO2 +HCl ------------ > CoHsN2Cl + Nacl+ 2H20

(Diazonium salt)

>» Reaction is carried out in a ice bath between the temperature 0-5°C
>» Itis also known as nitrite titration
> End point is determined by starch iodine paper or paste (External indicator) or by potentiometric method.

Mechanism of endpoint determination by using starch iodine paper

STEP 1: KI + HCl ------------------ > HuH+ka
STEP 2: 2HI + 2NaNO2 +2HCI ----------- > bh+2NO+ 2Nacl+ 2H20
STEP 3: I2 +Starch mucilage ------------- > Blue colour End point

The end point is detected by the formation of the blue colour with starch iodide paper.This is prepared by
immersing the filter paper in the starch mucilage and potassium iodide solution.

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UNIT-IT =DIAZOTIZATION TITRATION

Methodology:
Preparation and standardization of 0.1M Sodium Nitrite Solution( NaNO2)

Take 7.5 g of sodium Nitrite and dissolve in 850 ml of distilled Water and finally make up the volume
upto 1000ml

Standardization against Sulphanilamide:

 

Take 0.3 g of sulphanilamide dissolved in the hydrochloric acid(50ml) solution & 3 g of KBr
(potassium bromide),Cool in ice bath and and titrate against prepared 0.1 M NaNo? till the end
point.Endpoint is determined by potentiometry.

NaNO2 + HCl 0 wee > HONO + NaCl

(Sodium Nitrite) (Hydrochloric acid) (Nitrous acid) (Sodium chloride)

 

FACTORS AFFECTING THE DIAZOTIZATION

1. Acid concentration.

2. pH of the NaNO2.

3.Temperature of the reaction (should be maintained at 0-5 °C):

4.Reaction time (it takes 10-15 min)

5.Slow diazotizable groups: sulpha groups, carboxylic groups and nitrogen oxide group.

6.Fast diazotizing groups: anilide, toluidine and aminophenol.

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UNIT-IT =DIAZOTIZATION TITRATION

Types of Diazotization Titrations (or) Methods of Diazotization Titrations
There are mainly three types of methods based on the titration procedure. They are as follows:

1.Direct method: In this method is to treat the amino group containing drug with the acid
solution. The Obtained solution is immersed in the ice water bath at the temperature 0-5 °C. The
cooled solution is titrated with the sodium nitrite solution. The end point is determined by the
several methods.

2.Indirect method: In this method is that the excess nitrous acid is added to the titration sample
solution and it is back titrated with the another titrant. This method is mainly used for the
titration of insoluble diazonium salts.

3.Other method: The main principle involved in this method is the formation of the diazo oxide
which is more stable than the diazo compounds. For example, the aminophenol is readily
oxidized by the nitrous acid and converted to the quinones in the presence of copper sulphate
solution and forms the diazo oxide compounds.

ADVANTAGES:

» Selective for the all types of sulphonamides.
» Sensitive
> Reproducibility

DISADVANTAGES:

Applicable for a very less variety of samples.

Relatively slow when compared to other methods.

Temperature conditions to be properly maintained throughout the reaction.
The end point detection is very difficult.

The colour produced is not stable.

Lack of specificity.

VVVV VV

APPLICATIONS :

Â¥ Animportanat pharmaceutical application of sodium nitrite titration is the analysis of
sulphonamides by diazotization of primary aromatic amino group usually present in this
class of drug.

Â¥ Several sulphonamides require the formation of primary amine prior to diazotization step

Â¥ Eg.Phthalyl sulphathiazole & succinyl sulphathiazole are first hydrolyzed to give primary
aromatic amine & determined by sodium nitrite titration method

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UNIT-IT =DIAZOTIZATION TITRATION

5 MARKS :

1.Write a note on Diazotization titration.

2 MARKS :

1.Define Diazotisation titration

2. Principle involved in Diazotisation titration
3.What are types of Diazotisation titration

3.Application of Diazotisation titration

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UNIT-IV OXIDATION-REDUCTION (REDOX) TITRATIONS

REDOX TITRATION:

Â¥ Inchemical reacions in which electrons are transferred from one atom to another atom are known
as oxidation-reduction reactions. (OR)

Â¥ The oxidation-reduction reactions are conveniently known as redox reactions. (OR)

Â¥ A Titration which deals with a reaction involving Oxidation & Reduction of certain chemical
species.

Â¥ The two terms oxidation and reduction can be defined in different ways :

REDUCTION:

» Addition of Hydrogen to a substance

> Removal of Oxygen to a substance

» Addition of electron to a substance

> Reduction in Oxidation state of a substance.

OXIDATION:

Addition of Oxygen to a substance
Removal of Hydrogen to a substance
Loss of electron to a substance

Increase in Oxidation state of a substance

VVV WV

 

Redox Reaction
|

 

 

 

[
Oxidation
|
Loss of Electrons Gain of Electrons

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Increase in
Negative Charge

 

Increase in
Positive Charge

 

Decrease in Decrease in
Negative Charge} | Positive Charge

 

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UNIT-IV OXIDATION-REDUCTION (REDOX) TITRATIONS

CONCEPTS OF OXIDATION AND REDUCTION
OXIDATION:
> The term Oxidation means addition of oxygen to a substance and removal of hydrogen.

2Mg + O2— 5 2MgO0
Lt

-(2ex2) oxidation

The reaction between magnesium metal and oxygen to form magnesium oxide involves the oxidation of
magnesium.

REDUCTION:
>» The term reduction means removal of Oxygen from a substance and addition of hydrogen

EXAMPLE:

Cu0+Mg —— cu+Mg0

 

Reduction by loss of oxygen

The reaction between Copper metal and magnesium metal is an example of the reduction of Copper
oxide to Copper metal.

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UNIT-IV OXIDATION-REDUCTION (REDOX) TITRATIONS

OXIDIZING AND REDUCING AGENT
Oxidizing agent:

A species that oxidises another species and itself get reduced in the process and gains electrons from the
reducing agent.

EXAMPLE :
Most commonly used oxidizing agent in titrimetric analysis are

potassium permanganate
Potassium bromate
Potassium iodate

Ceric ammonium sulphate.
Iodine.

VVVVV

Reducing agent:

A species that reduced another species and itself get oxidized .In this reaction the reducing agent loses
electrons which are gained by the oxidizing agent.

Most commonly used reducing agents in titrimetric analysis are

Sodium thiosulphate
Ferrous ammonium sulphate
Titanous chloride

Titanous sulphate

VVV WV

THEORY OF REDOX TITRATION :
Electrochemical cell:

A device producing electric current from a chemical reaction(redox reaction).

ie, chemical energy to electrical energy.

They are constructed by two half cell and joined by salt bridge

In electrochemical cell , two half cells are present and they are basically electrodes, catogarizes
into two types

SAMAK

*~* Reference electrode

%

¢¢ Indictor electrode

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UNIT-IV OXIDATION-REDUCTION (REDOX) TITRATIONS

Voltaic Cell extemal
load ¥ cinucit

cathode id
salt bridge anes

Zn

 

CuS04 fag enSO4f aq)
hatt-cell (reduction) halt cell ( ceeid ation)

 

 

 

Reference electrode:

¢ It also known as standard electrode

* It has known electrode potential(E°)

* Completely insensitive to the analytes.

*  Eg:Standard hydrogen electrode(SHE) E°=0.00v

Saturated calomel electrode (SCE) E°=+0.28v Or -0.28v

Indicator electrode:

* For the determination of analyte concentration.

¢ Used in conjugation with reference electrode

*  Eg:platinum electrode
Example:

Reference electrode ----- Saturated calomel electrode (SCE);

Indicator electrode ---- Platinumelectrode (Pt electrode)

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UNIT-IV OXIDATION-REDUCTION (REDOX) TITRATIONS

HALF REACTION:

» Redox reaction involves oxidized & reduced species.

> Oxidation & Reduction occurring in a redox reaction should be studied separately to determine
the number of electrons transferred.

» This can be achieved for aqueous solutions by separating the redox reaction into two portions
called half reactions;one reaction for oxidation and other for reduction.

Half reaction at SCE,

* 2Hg+2Cl- €> Hg.Cl.+2e [oxidation] (anode)Eo=-0.28
Half reaction at Pt electrode,

*  Fe**+1le ---->Fe�* [reduction] (cathode) E°=0.77V

*  Ce*t4le -->Ce* [reduction](cathode) E°=1.61V

» Need to determine the potential difference between an electrode and a solution.
» It measured by using nernst equation.

NERNST EQUATION

This equation was first derived by the german chemist, WAITHER NERNST
The emf of a cell depends on the concentration of ions and on gas pressures.
The emf of cell provide a way to measure ion concentrations

VVV WV

We can relate the cell emfs for various concentration of ions and various gas pressure to
standard electrode potentials.
When a metal immersed in a solution containing its own ions , eg: zinc in zinc sulphate

Vv

solution.
» A potential difference is established between the metal and the solution.
» The potential difference (e) for an electrode reaction,

MN* + NE’ ----->M

An electrode reaction is expressed as,

 

R — Gas constant n— Charge number of ions
T — Absolute temperature M- Activity of the ions in the solution
F — Faraday constant Eo — Constant

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UNIT-IV OXIDATION-REDUCTION (REDOX) TITRATIONS

REDOX POTENTIAL:

The direction of an Oxidation & reduction reaction can be predicted only if some quantitative
characterisitic of the relative force of oxidizing & reducing agents involved is known.This characteristic
is called the redox potential.

REDOX INDICATORS (OXIDATION —REDUCTION INDICATORS)

>» Anredox indicator is a compound which exhibits different colours in the oxidised and reduced
forms.

» The reaction should be reversible and should give precise and sharp end point.

» Such indicators are known as Oxidation — reduction (or) redox indicators.

Examples of oxidation & reduction Indicators:

¢¢ Internal indicator
¢¢ External indicator
~¢ Self indicator.

INTERNAL INDICATOR:
1.Ferroin sulphate
2.Diphenylamine

FERROIN SULPHATE :

> One of the best oxidation — reduction indicators is the 1,10 — phenanthroline iron complex.

> It is bright red colour formed by combination of the base, 1,10 — phenanthroline with iron
sulphate with the ratio 3(base): 1 (iron)

>» when it get oxidized the colour change to pale blue.

» This indicator is used in titration of iron by cerium sulphate.

 

Ferroin sulphate (1,10 — phenanthroline iron complex sulphate )

[ (CigHsN>) 3 Fe] * ---------------— > [(CuHsNo); Fe] ** +e
Deep red Pale blue

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UNIT-IV OXIDATION-REDUCTION (REDOX) TITRATIONS

SUBSTITUTED FERROIN INDICATORS:
NITROFERROIN :

> 5-nitro-1,10- phenanthroline iron sulphate.
» It suitable for titrations using cerric(IV) in nitric or perchloric acid.

DIMETHYL FERROIN:

> 4,7- dimethyl- 1,10- phenanthroline iron sulphate
> Its useful for the titation of ferrous(II) with potassium dichromate in 0.5N sulphuric acid

EXTERNAL INDICATOR:

>» It has limited use, because after end point the excess titrant is reacted with a suitable reagent.

» This reaction between indicator & the analyte may sometimes be an irreversible one & in some
cases may lead to precipitation.

> So the end point is marked by failure.

> Such indicators are called as external indicator.

Example:
1.Potassium hexacyano ferrate

>» It used in titration of iron( II) by potassium dichromate.

» Drops of the solution removed to a spotting tile during the titration will give a deep Prussian blue
colour with Potassium hexacyano ferrate , because ferrous ions are still present

» At the end point,Iron only is present and this does not give a colour with potassium hexacyano
ferrate .

SELF INDICATOR:

>» Many times the titrant itself may be so strongly coloured that after he equivalence point.a single
drop of the titrant produce an intense colour in the reaction mixture.

> Such indicators are called self indicators.

> Self indicators generally are strong coloured as a result of change transfer transitions in them.

Example:
1. Potassium permanganate
2. Iodine solution

3. Cerium sulphate

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UNIT-IV OXIDATION-REDUCTION (REDOX) TITRATIONS

Potassium permanganate:

* It is powerful oxidizing agent, upon oxidation it produce pink colour.

* The purple colour of permanganate disappears under reduction(colourless).

* When all the reducing agent are titrated, the excess drop of permanganate produce pink colour.
Iodine solution:

* The dark brown colour of iodine disappears into colourless (reduction) as a result of I, to I� ions.

Cerium sulphate:

* Yellow colour is reduced into colourless.

TYPES OF REDOX TITRATIONS :

REDOX TITRATION TITRANT
>» Bromatometry Bromine
> Cerimetry Cerium(IV) salts.
» Dichrometry Potassium dichromate.
» Todometry NajS.0
>» Tlodimetry Iodine (I,)
> Permanganometry Potassium permanganate.
PERMANGANOMETRY :

Â¥  Permanganometry is one of the method of redox titrations where the solutions of potassium
permanganate are used.

Potassium Permanganate is a powerful Oxidizing agent.

Potassium Permanganate solution is always taken in the burette as the titrant.

It is also used as a Self indicator.

The end point is appearance of faint pink colour.

Potassium Permanganate Evolves nascent oxygen in acid which is responsible for the
Oxidation.

SLR KK

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UNIT-IV OXIDATION-REDUCTION (REDOX) TITRATIONS

NOTE:

Potassium Permanganate solution is standardized by titration against using

PRIMARY STANDARD SECONDARY STANDARD
Sodium oxalate

Arsenic trioxide Sodium thiosulphate

Oxalic acid

Ferrous ammounium sulphae

PRINCIPLE :

Potassium permanganate is reacted with oxalic acid in presence of sulphuric acid to form
potassium sulphate with manganese sulphate and by carbonic acid.

REACTION:

Molecular equations
2KMn0, + 3H,SO, » K,80, + 2MnSO, + 3H,0 + 5{0}
COOH

wm 70%
2H,0 + (0) »2CO, + 3H,0] x5
cooH

 

COOH
2KMnO, + 2H,S0, +5 , 2H,0 ——+ K,SO, + 2MnSO, + 18H,0 + 10C0,
cooH

 

PREPARATION OF POTASSIUM PERMANGANATE:

Â¥ Dissolve 3.2g of potassium permanganate in 1000ml of water.
Â¥ Heat on a waterbath for 1 hour

Â¥ allow to stand for 2days

Â¥ Filter through glass wool

STANDARDIZATION OF POTASSIUM PERMANGANATE:

Â¥ Take 20ml of oxalic acid solution in conical flask

Add 5 ml of sulphuric acid

Warm the mixture to about 70°C

Then fill the burette with Potassium permanganate Solution
Start titration and until reach the endpoint

Record the reading of burette.

SLR K

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UNIT-IV OXIDATION-REDUCTION (REDOX) TITRATIONS

aaneennennnnne >KMno, (Secondary standard)

final

 

lO wacenncceene > Oxalic acid + sulphuric acid

End point: pale (Primary standard)
permanent

pink color

Applications:

It is used for the assay of hydrogen peroxide (H202)
It is used for determination of nitrates and perchloric acid
It is used for assay of ferrous sulphate and ammonia sulphate

VVV WV

It is used for determination of calcium as calcium oxalate

ASSAY OF HYDROGEN PEROXIDE:
Principle:

It is assayed by permanganometry method in redox titration. Hydrogen peroxide is a oxidizing
agent because it liberates oxygen readily in acidic medium

2kMno4+3H2SO4 ----> k»SO4+2MnSO4+3H20+5[O]
5H20.+5[O] ----> 5H»0+50>

2kMnQ,4+3H2$044+5H2O---->K»S 04+2MnSO,4+8H20+502

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UNIT-IV OXIDATION-REDUCTION (REDOX) TITRATIONS

Procedure:

Â¥ From 20volume 6%w/v solution, pipette out 1ml of hydrogen peroxide

v¥ Add 20ml of 1M Hoso4

Â¥ Titrate with 0.02M potassium permanganate.

Â¥ Each ml of 0.02m kmno4 is equivalent to 0.001701 of hydrogen peroxide.

Potassium
permanganate

Hydrogen
peroxide

CERIOMETRY : [Ce ( NHy)4 (SOq)4 . 2 H2O]

>» It is a Oxidation reduction reaction

>» Ceric ammonium sulphate in sulphuric acid can function as oxidizing agent.
>» Itis more stable than potassium permanganate.

» Sulphuric acid — it used to prevent hydrolysis and precipitation

Principle:

In this titration arsenic trioxide reacts with sodium hydroxide to give sodium arsenite
This sodium arsenite is oxidised to sodium arsenate by cerric ammonium sulphate.

The reaction is very slow at the ordinary temperature.

Hence it is necessary to add osmic acid is added as a catalyst using ferroin as a indicator.

VVVV WV

The first sharp colour change to pink orange red to pale blue.

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UNIT-IV OXIDATION-REDUCTION (REDOX) TITRATIONS

ASO; + 6NaOH_ ------------- > 2Na3ASO3 + 3H20

Arsenic trioxide Sodium hydroxide Sodium Arsenite

2Ce (SO,)2 + Na3ASO; + H20 ------ > Ce (S04), + Na,ASO, + HeSO4
Cerric sulphate sodium Arsenite Cerrous sulphate sodium arsenate

PREPARATION OF 0.1M CERRIC AMMONIUM SULPHATE:

» Dissolve 65g of cerric ammonium sulphate in a mixture of 30ml of sulphuric acid and
500ml of water with gentle heat .

» Cool and filter the solution.

>» Dilute to 1000ml with water.

» Standardize the solution

NOTE:

We can standardize the cerric ammonium sulphate solution by using the following primary
standards.

>» Arsenic trioxide
>» Sodium oxalate
> Ferrous sulphate

Standardization of 0.1M ceric ammonium sulphate:
Procedure:

Weigh 0.2 of arsenic trioxide (previously heat at 1050c for 1 hour)

Transfer into 500ml conical flask.

Wash down the inner walls of the flask with 25ml of 8% sodium hydroxide solution.
Add 100ml water and mix well.

Add 30ml of dilute sulphuric acid, 0.15m1 of osmic acid solution and ferroin solution.
Then fill the burette with ceric ammonium sulphate solution

The end point is pink colour changed into a very pale blue

VVVVV VV

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UNIT-IV OXIDATION-REDUCTION (REDOX) TITRATIONS

 

Cerric ammonium sulphate (Titrant)

 

 

 

 

Arsenic trioxide + sodium hydroxide +dilute
Sulphuric acid + 0.15ml of osmic acid + ferroin Indicator

 

Endpoint - Pink colour changed into a very pale blue

 

 

 

ASSAY OF FERROUS SULPHATE:
Principle:

Â¥ Ferrous sulphate can be assayed by titrating with oxidizing agent ceric ammonium
sulphate using ferroin as indicator.

Â¥ ceric ammonium sulphate oxidises ferrous sulphate in acidic medium in sulphuric acid
medium to ferric sulphate.

Â¥ Ferroin sulphate is an indicator used in this titration.

2FeSO4 +2 (NH4)2 Ce (SO4)3 worsscssan > Fe(SO4)3 +2 (NH4)2 SQ4 +Ce (SO4)3
Ionic equation,in short

Fe + Cet -n------------ > Fe* + Ce*

Procedure:

Weigh accurately 0.5gm Ferrous sulphate

Dissolve in the mixture of 30m1 of water

Add 20ml of 1M Sulphuric acid

Titrate with 0.1M Cerric ammonium sulphate using ferroin as indicator until red colour
disappears

Each ml of 0.1M Cerric ammonium sulphate is equivalent to 0.01519gm of FeSO,

VVV WV

Vv

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UNIT-IV OXIDATION-REDUCTION (REDOX) TITRATIONS

IODIMETRIC TITRATION :
Definition:

Â¥ Oxidation & Reduction process involving Iodine is called in general Iodimetric titrations.
Â¥ Determination involving direct titration with iodine due to the oxidizing power of iodine
in aqueous solution is called as iodimetry.

Principle:

Â¥ Jodine is a mild oxidizing agent.

Â¥ The reversible reaction can be applied in analaysis of reducing agent such as thiosulphate
and arsenites by iodine.

Â¥ In most of direct titration with iodine of iodine in potassium iodide is employed, the
reactive species is tri iodide ion

bh + 2e <> 2I-

(Blue colour) (Colourless)
Hence all equation involving reaction of iodine should be ,
I; +2803� --------- >3I+ S4O¢� [MORE STABLE]
1)+2S.03� ---------- >2T+840,5� [LESS STABLE]
The equation usually used in terms of molecular iodine rather than tri-iodide ion
1b+2Na2S.03 ----------- >NaoS40g6 + 2Nal
Preparation of standard iodine solution (0.05M)

0.335¢ of iodine dissolve in 1000ml of water at 25°C.

Due to vapour pressure of iodine ,volataillasation happens.

It decrease the concentration during solubility.

To overcome this, dissolve the iodine in an aqueous solution of potassium iodide.
The solubility of iodine increase due to formation of tri-iodide.

VVVV VV

Precaution: keep the vessels containing iodine closed.

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UNIT-IV OXIDATION-REDUCTION (REDOX) TITRATIONS

Standardization of iodine solution:
The iodine can be standardized by using,

* Primary standard: Arsenic trioxide

* Secondary standard: Sodium thiosulphate
Standardization of iodine using sodium thiosulphate:
Procedure:

* Transfer 25ml of 0.05M iodine solution to conical flask

* Dilute to 100ml! with water

*  Titrate with standard thiosulphate solution.

* The solution become pale yellow colour

* Add 2ml of starch solution and continue the addition of thiosulphate solution slowly until
the solution become colourless.

Burette Holder

So

 

 

 

sodium thiosulphate

 

 

 

 

 

Iodine solution + Potassium iodide + Starch indicator

Support
Stand

 

 

Endpoint - Blue colour to Colourless

 

 

 

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UNIT-IV OXIDATION-REDUCTION (REDOX) TITRATIONS

IODOMETRY
Definition:

>» The titration in which the equivalent amount of iodine is liberated from the potassium
iodide by the sample and the liberated iodine is titrated against standard sodium
thiosulphate.

>» Itis indirect titration for determining the strong oxidizing agent

Principle:

» In this method, an equivalent amount of iodine is produced when the sample oxidizes
potassium iodide in the presence of mineral acid.

» The equivalent amount of iodine liberated in this way can be measured by titration with
standard sodium thiosulphate solution using starch mucilage indicator towards the end of
the titration.

KIO; + SKI + 3HSQOx, ----------- >3K,SO, + 31+ 3HO
Potassium Potassium sulphuric Potassium Iodine Water
Iodate Iodide acid sulphate
I, + 2 NaS,03  -ne-------- > NaS. + 2Nal
Iodine sodium thiosulphate sodium tetrathionate sodium iodide

Preparation of standard solution of sodium thiosulphate:

» Sodium thiosulphate is readily obtainable in the state of high purity.
>» Weigh 25gm of sodium thiosulphate

» Dissolve in few ml of water

>» Make up the volume with water upto 1000ml1

NOTE: Standardization of 0.1M sodium thiosulphate solution by using

Â¥ Primary standards: Potassium bromate, potassium iodate, potassium dichromate
Â¥ Secondary standards: Iodine solution, cerium sulphate, potassium permanganate

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UNIT-IV OXIDATION-REDUCTION (REDOX) TITRATIONS

Procedure ; Standadization using potassium Iodate:

Definite volume of potassium iodate solution was taken in a conical flask

Add excess of potassium Iodide & Dilute Hel acid added

Titrate the liberated iodine with sodium thiosulphate solution.

Starch Solution is added as Indicator,blue black solution form indicating the presence of
iodine.

SARK

xq

The blue solution was titrated against a drop of sodium thiosulphate , blue black colour
disappeared to form a colourless solution

Burette Holder

ae.

 

 

 

sodium thiosulphate

 

 

 

 

 

 

 

 

 

 

   

Potassium Iodate solution + Potassium iodide + dil Hcl + Starch
indicator
Flask
— END POINT-Blue to Colourless
—_
Co)
lodimetry lodometry
lodine lodine solution is prepared lodine is formed in
chemical reaction c.
Titrand / titrant lodine (I,) lodide (I) s
lodine flask Not used used
[Reaction 4 or = | “s
| wh
(Oxidizng agent |, é | \ KIO; I+KIO>
5 3
Reducing agent Na,S,0; - ‘KI iodine flask
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UNIT-IV OXIDATION-REDUCTION (REDOX) TITRATIONS

BROMATOMETRY :
Titrant — Potassium bromate (KBrO3)
Analyte — Arsenite

Â¥ Potassium bromate is a powerful Oxidizing agent & Used as a primary standard
Â¥ Reaction takes place in acidic medium (Hcl is used)

KBr03 <------------ >K* + BrO3�

Â¥ Direct titration takes place

3ASO3~ +BrOQ3 90 <-----e > 3ASO,* +Br_
SBr + BrO;. + 6H) < -2-neenen--a- >3Bn +3H,O
Br2 + Indicator = — ----+------------ > Colourless
(Methyl orange )
(Methyl red )

Steps involved in bromatometry :

1. Take the analyte solution (i.e. ASO3 * ) in a conical flask

2. Add 1M Hcl to the conical flask and make the solution acidic

3. Add 2-3 drops of Indicator solution (i.e. Methyl orange,Methyl Red) so solution becomes
Red in acidic medium

4. Titrate the above solution by using standard Potassium bromate solution

5. At the end point solution becomes colourless from red colour.

Burette - Potassium bromate (KBrO3)
Conical flask — Arsenite (Analyte) + Hcl + Methyl red (or) Methyl orange
Endpoint - Red colour to Colourless

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UNIT-IV OXIDATION-REDUCTION (REDOX) TITRATIONS

(OR)
Preparation of 0.1M Potassium Bromate

>» Weigh accurately 0.2784 g of potassium bromate into a beaker and dissolve it in
sufficient distilled water.

» Transfer the solution quantitatively into a 100 ml volumetric flask and make up the
volume to the mark.

Standardization of 0.1M Potassium Bromate solution with 0.1IN Sodium Thiosulphate

» Transfer an accurately measured volume of about 30.0 ml of 0.1 N potassium bromate
solution into a 250 ml iodine flask.

» Add to it 3.0 g potassium iodide, followed by 3.0 ml of hydrochloric acid.

» Titrate liberated iodine with 0.1 N sodium thiosulphate, using 3.0 ml of freshly prepared
starch solution as an indicator at the end-point.

» Each ml of 0.1 N sodium thiosulphate is equivalent to 0.002784 g of KBrO3.

DICHROMATOMETRY :

¢¢ Titrant — Potassium Dichromate ( K2Cr207)

“Analyte — Fe**

%* Potassium Dichromate is an Oxidizing agent and used as a primary standard substance.
%* Potassium Dichromate is used only in acidic medium

C1072" ion (Orange ) will reduces as Cr + (green)

K.Cr.O,7 penne > KK + CroO, >

CrO,* + 14H* +6e €-------- > 2Ccr* + 7H,O

“+ Tron ( Fe 2+) is used as analyte

6Fe 7* +CrO77" + 14H* €-------- > 2Cr** +6Fe ** + 7H5O

& Crh (green) in colour,which is Produced after reduction of Cr2O7 °-

“* By using simple indicator method,end point cannot be determined; So to determine the end
point external indicator method is employed.
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UNIT-IV OXIDATION-REDUCTION (REDOX) TITRATIONS

Steps involved in Dichromatometry :

Burette Holder

ae

 

 

Burette - Potassium Dichromate ( K»Cr.07)

Conical flask — Fe ** (Analyte) + H2SO, + Potassium
ferricyanide

Endpoint - Blue colour to Colourless

 

Support
Stand

 

 

1. Take the analyte solution (i.e. Fe** ) in a conical flask
Add H SO, provide the acidic medium

Titrate the above solution by using standard Potassium dichromate solution

a

Near the end point take a drop of solution from conical flask and put into the external
indicator.
5. End point is determined by using potassium ferricyanide indicator,when formation of

blue colour stops

(OR)
Preparation of 0.1M Potassium dichromate

Weigh accurately 0.49 g of potassium dichromate previously dried at 20°C for 4 hours and

dissolve in sufficient distilled water to produce 100 ml in a volumetric flask.

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UNIT-IV OXIDATION-REDUCTION (REDOX) TITRATIONS

Standardization of 0.1 M Potassium dichromate solution

To 20ml of above solution, add 1g of potassium iodide and 7ml of 2M HCI. Add 250ml water
and titrate with 0.1M sodium thiosulphate using starch indicator added towards the end point.

The end point is obtained when colour changes from blue to green.
Each ml of 0.1 M sodium thiosulphate is equivalent to 0.0049g K2Cr207.
APPLICATIONS :

1. Redox titrations are carried out for the quantitative analysis of various substance.

2. Redox titrimetry is used to analyse a wide range of inorganic analytes.

3. A Redox Titration can accurately determine the concentration of an unknown analyte by
measuring it against a standardized titrant.

4. Itis used for analysis of organic analytes.
There are numerous applications for the redox titration in chemistry,pharmaceutical

preparations,Environmental analysis,Agriculture and many more.

10 MARKS:

1.Write the principle of redox titration and give a note on indicators used in redox
titration.

2. Explain the concept of iodometry and iodimetry. Give the procedure for the
Standardization of sodium thiosulphate solution using potassium iodate.
5 MARKS:

1. Discuss the theory of redox titrations(OR) Concept of Redox titration (OR) Principle
Involved in Redox titration.

2. Explain the principle & Reaction involved in cerimetry
3. Explain in detail about permanganometry.
4. Explain in detail about bromatometry

5. Explain in detail about Dichromatometry

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UNIT-IV OXIDATION-REDUCTION (REDOX) TITRATIONS

2 MARKS :

Define Redox titration

Define Oxidation & Reduction

Define Oxidizing and reducing Agent with example

Half reaction

Nernst equation

Redox potential

Mention the types of redox Indicators (or) Classify redox indicator
Mention the types of redox titrations.

Co MON NDM BR WN

Distinguish between iodimetry and iodometry.

10. Differentiate between internal and external redox indicators.
11. What are self indicators? Give examples.

12. What is dichrometry

13. What is permanganometry

14. What is Bromometry

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UNIT-— V CONDUCTOMETRY

SYLLABUS: Introduction, Conductivity cell, Conductometric titrations, applications.

Definition :

>» Itis defined has as determination or measurement of the electrical conductance of an
electrolyte solution by means of a conductometer .
» Electric conductivity of an electrolyte solution depends on :
1. Type of ions (cations, anions, singly or doubly charged )
2. Concentration of ions
3. Temperature
4. Mobility of ions

PRINCIPLE:

» The electric conductance in accordance with ohms law which states that the stength of
current(i)passing through conductor is directly porportional to potential difference &
inversely to resistance.

i=V/R
Important definitions :
Conductance:(G) It is defined as the reciprocal to resistance (R)
G=I/R

Specific conductance (K): conductance of the body of uniform length(1) & uniform area cross
section(A)

K=I/R x IVA
Resistance (R):It is a measure of the conductors opposition to the flow of electric charge
R=l/G

Specific resistance:(p) It is resistance offered by a conductor of unit length and having unit
cross section

Rol/A

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UNIT-— V CONDUCTOMETRY

Ohms law :

Ohms law states that the current through a conductor between two points is directly proportional
to the voltage across the two points.

V=IR
V — Voltage
I— Current

R - Resisance

Conductivity cells:-

>» Made of pyrex or quartz and are fitted with two platinum electrodes.
» Should be placed in vessel containing water to maintain constant temperature

Types :
1. Type A 2. Type B 3. TypeC
Type A Conductivity cell :

This consists of the electrode placed at a larger distance & is used for the measurement of the
high conductance.

 

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UNIT-— V CONDUCTOMETRY

Type B Conductivity cell :

In this type, the cell is dipped in the sample solution to measure the conductance in the titrations.

 

Type C Conductivity cell :

> In this type,large electrodes are placed with small distance
>» This type cell is mainly used for the measurement of the low conductance
>» They are made up of glass fitted with the platinum electrodes

 

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UNIT-— V CONDUCTOMETRY

TYPES OF CONDUCTOMETRIC TITRATIONS :
1.ACID BASE TITRATIONS

2.PRECIPITATION TITRATIONS

3.REDOX TITRATIONS

4.COMPLEXOMETRIC TITRATIONS

5.NON-AQUEOUS TITRATIONS

1.A4CID BASE TITRATIONS :

In this method,the conductance of the hydrogen ions & hydroxyl ions are
compared with he conductivity of the sample.

>» Neutralization of strong acid with strong base. E.g HCl with NaOH
>» Neutralization of weak acid with strong base.E.g .CH;COOH with NaOH
>» Neutralization of weak base with strong acid.E.g HCl with NHsOH
>» Neutralization of weak acid with weak base.E.g-CH;COOH with NH,OH

Procedure :
1.The titrant is added from a burette to a beaker containing the analyte.

2.After every addition of a definite voume of titrant,change of conductance is
noted

3.The change of conductance as a function of added titrant is plotted to determine
the equivalence point.

4.The pattern of the plot will be different for different types of titrations

5.At the end point of the titration,there is a sharp change in the conductivity of a
solution as shown by the intersection of the lines in the graph of conductivity Vs
Volume of titrant added.

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UNIT-— V CONDUCTOMETRY

STRONG ACID WITH STRONG BASE
HCI Vs NaOH

[H* +Cl°]+[Na* +OH-]_ ---------------- >[Na* +Cl°-] +H.O

Vv

The initial conductivity of the Hcl solution is high because of the proton
from dissociation of the acid

Then titrating with NaOH dissociates into Na+ & OH-

This hydroxyl ion react with the H+ Ions to form the water.

This shows the decrease in the conductivity.

VVV WV

After completion of the reaction,the excess addition of the NaOH Shows the
increase in the conductivity

» The plot between the conductivity & the volume of the titrant shows the V
Shaped curve

Conductometric titration:
Strong acid vs Strong base

* equivalence
point/neutralisatio

oint is determinea
p

Conductance —+>

graphically

Volume of NaOH (mO—>

 

STRONG ACID WITH WEAK BASE

HCI Vs NH,OH

» Titrations of strong acid such as HCl with weak base such as the
ammonium hydroxide

HCl + NH,OH wor rr rrr r rn en > NH,Cl + H,O

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UNIT-— V CONDUCTOMETRY

Same as the titration of the strong acid withstrong base,it initially shows the
increase in the conductivity because of the H * ions

This conductivity is decreased by the addition of the weak base that is with
the NH,OH that neutralizes the H * ions with the OH ions & decreases the
conductivity.

The excess addition of the NH,OH does not show the change in the
conductivity

The plot between the conductivity & the volume of the titrant shows the
Plateau

Conductometric titration:
Strong acid vs Weak base

ae

* equivalence
pout/neut? alisation

pout ts determined

x graphically

}

Volume of N3,OH (mi)—~

Conductance

 

 

WEAK ACID WITH STRONG BASE.

CH;COOH Vs NaOH

The weak acid such as acetic acid is titrated with the strong base such as
sodium hydroxide.

CH;COOH + NaOH ----------------- > CH;COO Na +H,O

The acetic acid dissociates to produce the H+ ions which shows the high
conductivity & is titrated with NaOH which is dissociated to produce the
OH- ions which shows slight increase in the conductivity by the formation
of the CH;COO Na at the equivalent point

Then it shows the gradual increase in the conductivity by the addition of
excess titrant

The plot between the conductivity & the volume of the titrant shows the
Plateau 142

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UNIT-— V CONDUCTOMETRY

Conductometric titration:
Weak acid vs Strong base

*% equivalence
point/neutralisation

point is determined

Conductance ——>

graphically

 

 

Volume of NaOH(m) —

WEAK ACID WITH WEAK BASE.
CH3;COOH Vs NH,OH

> The weak acid such as acetic acid is titrated with the weak base such as
ammonium hydroxide.

CH;COOH + NH,OH ----------------- >CH3COO NH, +H,0

» The acetic acid is dissociated and it combines with the ammonium ion after
dissociation of the ammonium hydroxide

» This forms the ammonium acetate salt which shows the increase in the
conductivity

>» After attaining the equivalence point, the addition of the titrant does not
shows the conductivity change

» The plot between the conductivity & the volume of the titrant shows the
Plateau

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UNIT-— V CONDUCTOMETRY

Conductometric titration:
Weak acid vs Weak base

* equivalence
point/neutralisation
point is determined

graphically

Conductance —>

 

V

.

Volume of NH,OH (m{)—>

 

ADVANTAGES OF CONDUCTOMETRIC TITRATIONS :
1.No need of indicator
2. Coloured or dilute solutions or turbid suspensions can be used for titrations

3.Used for determining the concentration of weak acids,weak base ,mixture of weak & strong

acids.
4.Temperature is maintained constant throughout the titration

5.End point is determined accurately & errors are minimized as the end point is being determined

graphically.

DISADVANTAGES OF CONDUCTOMETRIC TITRATIONS :

1.Less accurate when compared to other methods because high concentration are not measured by the
conductometric titrations

2.The solutions are compulsory diluted for the measurements

3.Less satisfactory when compared to other methods

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UNIT-— V CONDUCTOMETRY

APPLICATIONS :

1.Used in the quantitative analysis of the compound

2.Used in the determination of the purity of the water

3.Used in the determination of salinity of the sea water

4.Used in the determination of the ionic product of the water

5.Used in the determination of sparingly soluble salts such as barium sulphate and lead sulphate
6.Used in the determination of the basicity of the acids.

(Basicity is defined as the number of carboxylic acid group attached to the molecule)
10 MARKS :

1.Write the principle and different types of titration involved in Conductometric
titrations.

5 MARKS :

1.Explain the general applications of conductometric titration.
2.Write the basic concept of conductometric titrations.

2 MARKS :

1.Define conductometric titration

2. Conductivity cells & its types

3. Advantages of conductometric titrations

4. Disadvantages of conductometric titrations

5. Conductance

6. Resistance

7. Ohms law

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UNIT-V POTENTIOMETRY

SYLLABUS:

Potentiometry- Electrochemical cell,construction and working of reference (standard hydrogen ,silver
chloride electrode and calomel electrode) and indicator electrodes (metal electrodes and glass electrode),
methods to determine end point of potentiometric titration and applications.

What is Potentiometry?

» Potentiometry is one of the methods of electroanalytical chemistry.

» It is usually employed to find the concentration of a solute in solution.

» In potentiometric measurements, the potential between two electrodes is measured using
a high impedance voltmeter.

Electrodes :

» Electrodes are mainly used to measure the voltages.
» Mainly two electrodes are used in the potentiometry

1. Reference electrode 2. Indicator electrode
ELECTROCHEMICAL CELL :
» Elecrochemical cell generate electrical energy from chemical reaction between sample and
titrant.
» Elecrochemical cell has two electrodes (reference electrode and indicator electrode)connected by
salt bridge.

CONSTRUCTION AND WORKING OF ELECTROCHEMICAL CELL:

ELECTROCHEMICAL CELL

Voltmeter

   
 

Cathode
(Reduction)

Anode
(Oxidation) | }Zn

 

 

 

— —

Zn(s) | ZnSO, (aq) || CuSO, (aq) | Cu(S)

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UNIT-V POTENTIOMETRY

>» The electrochemical cell consists of two electrodes of zinc and copper connected by a salt
bridge to form electrical circuit.

» These two electrodes are immersed into their respective solutions,that is zinc electrode is
immersed into zinc sulphate solution and copper electrode in copper sulphate solution .

» The electrodes are made into contact through wires connected to voltameter,secondly

through solution and a salt bridge.salt bridge consists of tube filled saturated salt

solution,Eg.kel solution.This results in formation of electric circuit.

The ends of the tube is capped with porous frits to avoid mixing of solutions.

The potential between two electrodes is measured by using a high impedance voltmeter.

Potential on an electrode depend on then ions present in a solution and its

concentration,this serves as a useful method to determine ions and their concentrations in

solution.

VV Vv

» Electrons move through electrodes and wires from zinc to copper electrode.

» In solution on the left,zinc ion move away from the electrode,and sulphate ions moves
towards the electrode.

» In solution on the right,sulphate ion move away from the electrode and copper ions move
towards the electrode.

» In salt bridge positive ion move towards right and negative towards left.

REFERENCE ELECTRODES

v¥ Reference electrode is an electrode which has a stable and well known electrode
potential.

v¥ These are mainly used for the determination of the analyte by maintaining the fixed
potential.

Eg.

(a) Standard Hydrogen Electrode,
(b) Saturated Calomel Electrode, and
(c) Silver-Silver Chloride Electrode.
Â¥ Reference electrode are classified into two main classes.

PRIMARY STANDARD ELECTRODE - Eg. Standard Hydrogen Electrode

SECONDARY STANDARD ELECTRODE - Eg. Saturated Calomel Electrode, and Silver-
Silver Chloride Electrode

Among these Silver-Silver Chloride Electrode is frequently used.

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UNIT-V POTENTIOMETRY

STANDARD HYDROGEN ELECTRODE (SHE):

>» Itis used as primary reference electrode.

>» The standard hydrogen electrode consists of a platinum electrode coated with platinum
black.

» The electrode is dipped in an 1M HCI solution which contains the hydrogens ions.

>» 1 atm hydrogen gas is passed over the platinum foil through the side tube at 25°C.

» Itcan act as a cathode as well as an anode.

Half cell reaction are given below :
If SHE is used as a cathode,the reduction reaction is

2H* (aq,1M)+ 2e7 — H2(g,1 atm) E° = 0 Volt
If SHE is used as a anode,the oxidation reaction is

Ho(g,1 atm) — 2H (aq,1M) + 2e7 E° =0 Volt

—__  »

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Wire to a
other half-cel H,(g)
CS (Lat)
,
Salt bridge to a
other half-cel aa
mo
Lt
Platinum
— |
>. H"(aq, 1M)
plus electrolyte
Ht
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UNIT-V POTENTIOMETRY

ADVANTAGES:

>» The standard electrode potential is ‘ 0 ‘ Hence in the determination of single electrode
potential of an unknown electrode using SHE as the reference electrode,it is equal to the
emf of the cell.

It can be used over the entire pH range.

It has no salt water

Electrode reaction is simple

It provide accurate results.

VVV WV

DISADVANTAGES :

» It is difficult to construct SHE

» It is difficult to obtain high pure H2 gas and to maintain 1M Hcl for a long time

» Since it is made of glass,care is needed to handle.

> Ptis highly expensive and it may get poisoned by the impurities present in H, gas & HCl
>» It is not suitable for redox reactions.

STANDARD CALOMEL ELECTRODE (SCE) :

> Calomel electrode is a secondary reference electrode electrode to determine the standard
potentials of the electrode.

Construction :

>» Mercury (Hg) is kept at bottom of jar.

> athin glass tube with a platinum wire is then inserted, taking care that the platinum wire
drips into mercury.

>» The mercury is then covered with a layer of mercury and mercurous chloride HgoClo
(calomel) paste.

» At top saturated KCI solution is poured

» KCl filled tube act as a Salt bridge

Working :

> The potential of the calomel electrode depends upon the concentration of the chloride
ions in solution.

» If the electrode is saturated calomel electrode (SCE), some crystals of KCL are placed
over the Hg-HgoCly

> Itcanactas acathode as well as an anode.

The electrode is represented as
KCl (Satu) / Hg, Cl: (s) / Hg ()
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STANDARD CALOMEL ELECTRODE (SCE)

Oxidation : 2Hg (1) + 2cl (aq) ----- > Hegncl, (s) + 2e7

Reduction : Hgocl) (s) +2e5 0 > 2He (1) +2cl (aq)

ADVANTAGES :

» The standard electrode potential is « 0.2422 V ‘ Hence in the determination of single electrode
potential of an unknown electrode using SCE as the reference electrode.

» It is cheap,compact & Easy to transport

» Its electrode is constant and easily reproducible

» Easy to construct and maintain the cell.

DISADVANTAGES :

> Solubility of kcl changes with temperature

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UNIT-V POTENTIOMETRY

SILVER/SILVER CHLORIDE REFERENCE ELECTRODE

VVVVVV

The silver/silver chloride reference electrode is a widely used reference electrode .
Because it is simple, inexpensive, very stable and non-toxic.

Silver wire is coated with layer of silver chloride

The wire is sealed in glass tube and dipped in KCI solution

KCI solution filled tube act as salt bridge

As a laboratory electrode , it is mainly used with saturated potassium chloride (KC)
electrolyte, but can be used with lower concentrations such as 1 M KCL.

salt badge (
Si
Chis

Elecin
Neh
-..-. | -..-- ] coating

glas

 

   

 

 

 

 
 

 

Ag w

 

 

 

 

olution_...

.

 

SILVER/SILVER CHLORIDE REFERENCE ELECTRODE

>
>
>

Changes in ionic concentrations also change the reference potential.
Silver chloride is slightly soluble in strong potassium chloride solutions,
so it is sometimes recommended that the potassium chloride be saturated with silver
chloride to avoid stripping the silver chloride off the silver wire.
The silver-silver chloride reference electrode develops a potential proportional to the
chloride concentration, whether it is sodium chloride, potassium chloride, ammonium
chloride or some other chloride salt and remains constant as long as the chloride
concentration remains constant.
Most of reference electrodes use a saturated KC] solution with an excess of KCl crystals.
The extra KCI dissolves into the electrolyte as the potassium and chloride ions diffuse out
through the liquid junction in normal use.

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UNIT-V POTENTIOMETRY

>» This extra buffer of KCl extends the time before the reference cell starts to drift due to
the depletion of chloride ions in the electrolyte.
> Itcanact as acathode as well as an anode.

The electrode is represented as

Ag/ AgCl / KCl (Satu)

Oxidation Ag + Cl� ----------- > AgCl+e

Reduction AgCl] +e ----------+- > Ag + Cl"

Advantage of Ag-AgCI electrodes over SCE.

> 1. It has high stability.

> 2. Non-toxic nature

>» 3.Simple instrumentation
> 4.Economical

Disadvantage of silver-silver chloride electrode

» 1. Itis more difficult to prepare than SCE
» 2. AgCl in the electrode has large solubility in saturated KC]
>» 3.It may cause silver precipitation

INDICATOR ELECTRODES

>» Indicator electrode is used to measure the potential of the analyte solution comparing
with that of the reference electrode.
> Its potential is directly proportional to the ion concentration

Eg.
Metal Electrodes

Glass Electrodes

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UNIT-V POTENTIOMETRY

GLASS MEMBRANE ELECTRODE:
It is the most commonly used ion selective Electrode.
Construction :

The measurement of pH for any given solution can be done easily using a glass electrode.
This is composed of glass tube at the top & thin walled glass bulb at the bottom

The bulb is filled with 1M HCl]

A Silver wire covered with silver chloride is present at the lower end of the glass tube
The portion of silver wire which is dipped in 1M HCLresulting in the formation of silver-
silver chloride electrode

» The overall setup is immersed in the sample solution

VVVV Vv

Working :

> It was found experimentally that at the interface of glass & solution,containing hydrogen
ions, potential difference exists.

> By considering a specific glass,if the hydrogen ion concentration changes,the magnitude
of potential difference also changes .

     
   
 

gC! coatedilll
“Ag wire y

 

 

ADVANTAGES:

It is simple to operate

It is used in large scale in laboratories associated with industry,chemical work.
It can be used in coloured,turbid and colloidal media

Special glass electrode can be used to measure pH upto 14.

It requires very small volume of test solution for measurements.

VVVV Vv

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UNIT-V POTENTIOMETRY

DISADVANTAGES:

It cannot be used in acid fluoride solution.

It cannot be used at high temperature for prolonged peroids

The bulb used in this electrode is brittle in nature,thus requires to be handled carefully
It will not work for pure ethyl alcohol,acetic acid .

VVV WV

METAL ELECTRODES

» Metal electrode develops electric potential as a result of redox reaction at its surface of
metal.

> Platinum or gold metals are used as indicator electrodes.

» These are very simple indicator electrodes

In potentiometry ,the following 3 types of metal electrodes are used:

1. First Order Electrode : These electrodes are composed of a metal rod immersed in its
metal solution and are responsible for the ionic activity of the electrode.

For example :

Copper electrode dipped in copper sulphate solution Cu? +2e ----> Cu

Silver electrode dipped in silver nitrate solution Agt +e ------- >Ag

2. Second order Elecrodes: These electrodes are made up of the metal wires coated with

the salt precipitates .They respond to the changes in the ionic activity by the complex
formation.

For example :
Ag/ Agcl/ kel, and Hg/ Hgoclo/ Kel.

3. Third order electrodes: These electrodes are also named as redox or inert electrodes
They are consists of an inert metal electrode dipped in a redox solution.

For example :

Pt-H> electrode.

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UNIT-V POTENTIOMETRY

 

METAL ELECTRODES

 

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UNIT-V

POTENTIOMETRY

METHODS TO DETERMINE END POINT OF POENTIOMETRIC TITRATION

METHODS TO DETERMINE END POINT

Method 1: Graph between electromotive

force (emf) and volume of titrant is
plotted.

Volume corresponding to maximum slope z

z

show the end point.

   

End point

 

 

volume ———>

end point

   
 

2

/ AV

>

AE

YH

 

 

volume ——>

ethod 3: Second derivative graph is
tween [(change in emf)? / (change in
jiume)] and volume of titrant.
ume corresponding to zero in graph
w the end point.

156

Method 2: First
between (change
volume) and volume of titrant. |

Volume corresponding
from peak of graph show end

Method 4: Gran’s plot is bet
potential and volume of titra
A straight line is obtained, an
decreases to zero at end poin

antilog E —>

\

   
    
   
 
   
    

|

 

volume

Derivative Grar
in emf / chang

ANC

tow

End point
volume

 

 

 

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UNIT-V POTENTIOMETRY

APPLICATIONS :

VVVVV VV VV VV

Used in the determination of the % of acetyl salicylic acid in aspirin tablets
Used in the determination of the % of acetic acid in the vinegar

Used in the determination of the carbonate

Used in the acid base titrations

Used in the precipitation titrations

Used in the Complexometric titrations

Used in the Redox titrations

Drug Analysis in Pharmaceutical industry

Food industry for analysis of quality

Useful for environmental analysis by use of ion selective electrodes

Different components of mixture can be analysed by potentiometric titrations.For this
purpose,differential titrations are carried out by potentiometric titrations

ADVANTAGES:

>

In comparision to another techniques of analysis,potentiometry is less time consuming &
cheapest method of analysis

Useful for various types of reactions like acid base,redox,precipitation &
Complexometric titrations

No need to add external indicator

Applicable for titrations in non aqueous medium

Applicable for analysis of dilute solutions with high degree of accuracy

DISADVANTAGES:

>

>

Interpretation of data is made from titration curves,which may lead to generation of
errors,this affects the accuracy of potentiometric titrations

Ion selective electrodes may respond to more than one analyte or componenets other than
analyte.this affects the selectivity of ion selective electrodes.

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UNIT-V POTENTIOMETRY

10 MARKS:

1.

Explain in detail the construction and working of silver silver chloride electrode.

5 MARKS :

1.

we

Describe the construction, working,advanages & Disadvantages of Standard hydrogen
Electrode

Write the construction and working of calomel electrode

Explain in detail about glass membrane electrode

Explain in detail about Metal electrode

2 MARKS :
1. Give any two important applications of potentiometry.
2. Mention the indicator electrode used in Potentiometry.
3. Define Reference electrode with example
4. Define Indicator electrode with example
5. Define Potentiometry.
6. Electrochemical cell
7. Advantages & Disadvantages of potentiometry

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UNIT-—V POLAROGRAPHY

SYLLABUS:

Principle ,[Ikovic equation,construction and working of dropping mercury electrode and rotating
platinum electrode,applications

DEFINITION OF POLAROGRAPHY :

 

> Itis an electroanalytical method.

» Itis used to identify & Estimate the electroactive material like metal ion present in the
solution.

» It involves the study of current voltage relationship at a dropping mercury electrode
under certain controlled condition

» Jaroslav Heyrovsky developed an apparatus called Polarograph which increases the
applied voltage at a steady rate & record the current voltage curve called polagram.

>» The term polarography is used when a dropping mercury electrode is used as the
working electrode (Cathode)

>» General name for this method is voltammetry

PRINCIPLE OF POLAROGRAPHY :

 

> During an electrolysis the reduction containing metal ion undergo reduction.

Cd** 42e 0 ---------- > Cd
>» The metal ion undergoing reduction may reach the surface of the electrode by
polarographic currents such as Migration,diffusion & convection current.

POLAROGRAPHIC CURRENTS

1.Residual current

2.Migration current

3.Diffusion current

4.Limiting current or Kinetic current

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UNIT-—V POLAROGRAPHY

1.Residual current
» Combination of current produced by reduction of impurities,current produced by
Helmholtz double layer.
Ir =If + 1c
ir = residual current
if = Faradic current — due to impurities
ic = Non faradic current or capacitive current — due to electric double layer(Helmholtz double
layer) (OR)
The point from A to B a small current flow this is known as Residual current is carried by

supporting electrolyte & impurities present in the sample.
2. Migration current

>» The charged particles migrate towards the electrode surface under the influence of the

applied voltage.
3.Diffusion current

>» The particles (charged or not) present in the solution diffuse towards the electrode surface
under the influence of concentration gradient.
>» The value of diffusion current using dropping mercury electrode is given by IIkovic

equation

IIkovic equation

id=607ncD�? m~ t'�

id = Diffusion current

607 = A combination of numerical constants ; n = number of electrons
D = Diffusion coefficient of metal ion ; C = Concentration of metal ion
M = Mercury flow rate ; t = Drop time in sec

Diffusion current is directly proportional to the concentration of electroactive metal present in

the solution( DIFFUSION CURRENT Of CONCENTRATION )

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UNIT-—V POLAROGRAPHY

4.Limiting current or kinetic current:

At the point C,all the metallic ions are reduced.As no more metallic ions,so no further increase of
current and now the current remain constant.This constant current is known as Limiting current

   
   
    

 

D
Limiting current ©
< ema eee eee em em eee

tT
ra
a
: Diffusion
i cutrent
—
3
rs)

Residual. Cur

+-

A Half wave

potential

 

Applied Voltage >

Half wave potential :

» The potential at the point on the current voltage curve,where the current is

equal to one half of the diffusion current is called as Half wave potential.

> It is denoted by (E �)
>» At this potential 50% of the reduced form & 50% of the oxidized form are

present.

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UNIT-—V POLAROGRAPHY

DROPPING MERCURY ELECTRODE

> In Polarography,the working or indicator electrode is DME

> Dropping Mercury Electrode (DME) — act as CATHODE (Negatively charged /
polarizable)

> Mercury pool —Reference electrode ,act as ANODE(Positively charged/Non polarizable
because of is large surface area

 

Cathode
J PA
aa)
Dropping mercury mAy—
Mercury reservoir T electrode -
Vv

 
  

 

 

Nz + 6

 

Air outlet

 

 

    
 

 

 

 

——

Battery

 

Capillary
tube ~

Rubber tube

 

 

 

 

 

 

Analyte (electrolyte)

KCI (Supporting analyte)
> Mercury pool

Working & construction :

>» DME is preferred because it allows quick formation of new mercury surface
at each and every second in the on going analytical procedure
The reservoir is filled with mercury

Fine drops of mercury is allowed to flow from the tip of the capillary tube.
The capillary is connected to mercury reservoir by rubber tubing
Capillary tube of about 8 — 30 cm

Diameter of the mercury drop should be 0.5 to 1 mm.

A Platinum wire is inserted into the mercury for electrical contact

New mercury drop forms,grows and fall for every 2 to 6 seconds

At the applied voltage above + 0.4V mercury is oxidized to mercury I

VVVV VV VV V

DME can be used only for the analysis of reducible (or) easily oxidisable
substance

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Vv VVV WV Vv

Vv

UNIT-—V POLAROGRAPHY

Nitrogen gas Inlet & outlet are provided in the cell for expelling the
dissolved oxygen

Otherwise it will reduce at the DME & Produce its own polarogram in
addition to the original polarogram

Remove Oxygen by passing N>( 10 mins before the reaction)
Galvanometer measures the current

Voltmeter measure the applied potential

The drop time can be controlled by a mechanical knocker that will help to
dislodge the drop at a fixed time after the drop begins to form.
Then,gradually increasing voltage is applied to the polarographic cell &
current is recorded.

Graph is plotted between voltage applied & current

This graph is called polarography and the apparatus is known as polarogram

ADVANTAGES OF DME

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>

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>

Mercury being a noble metal ,it do not react with constituent of electrolytic
solution

It is responsible for the formation of amalgam with various metals,which
leaves clean surface.

Due to high hydrogen over voltage of mercury, DME is widely used.

It also provides a smooth,fresh surface for reaction

DISADVANTAGES OF DME

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>
>
>
>

Capillary is very small and thus can be easily blocked

Mercury is highly toxic and poisonous

Mercury has measurable vapour pressure

Continual dropping of mercury make this method costly

Mercury used in DME must be highly pure,this make this method costly.

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UNIT-—V POLAROGRAPHY

ROTATING PLATINUM ELECTRODE

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It is also known as Rotating platinum Micro Electrode ( RPME) .

Instead Dropping Mercury Electrode RPME can be used.

DME has disadvanages that it cannot be used at high potential due to
Oxidation of mercury.

Therefore,Platinum electrode is used in such cases.

Platinum electrode is stationary then diffusion current will be slowly
attained,so to overcome this problem platinum electrode rotated at a constant
speed,which increasing sensitivity and rate of attaining steady diffusion
current.

Construction & Working of rotating platinum electrode :

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>

The electrode is constructed from a standard seal.

It consists of about 5 mm platinum wire having 0.5mm diameter below
standard mercury seal by passing through small hole.

A wire from mercury seal is connected to the source that applies voltage.
The tubing forms steam of the electrode which is rotated at a constant speed
of 600 rpm.

Rotating platinum electrode is used as an indicator electrode.

Elecrical connection is made to the electrode by copper wire passing through
tubing to the mercury covering the platinum wire seal

To the analyte solution supporting electrolyte like Kcl is added.(1.e., 50 -100
times of sample concentration.

Pure Nitrogen Gas is bubbled through the solution to expel out the dissolved
oxygen.

Potential is applied across the electrodes and titration is started.

A Graph is plotted between the volume of solution added v/s diffusion
current & End point is detected.

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UNIT-—V POLAROGRAPHY

ADVANTAGES :

>» The electrode is simple to construct.

» The rotating platinum micro electrode can be used at positive potential upto + 0.9V
Whereas DME range -2V to +0.4V.

» It is more sensitive because diffusion current is 20 times larger than in the case of DME.

    

 

COPPER WIRE

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MERCURY

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APPLICATIONS OF POLAROGRAPHY :

» The quantitative polarography helps in determining the dissolved oxygen

>» Polarography is also used widely for determining the trace metals,especially in drugs
having a metallic constituent.

>» The metals that are estimated by using polarography include
antimony,cadmium,iron,magnesium,zinc,mercury,copper & arsenisc.

165

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UNIT-—V POLAROGRAPHY

» In pure solution ,estimation of both fat soluble & water soluble vitamins is done by either
oxidation or reduction with the help of DME

>» Antibiotics can also be determined by polarographic methods

>» Apart from its analytical use,poloarography is also used in physical,inorganic & organic
chemistry for research works.

>» Polarography is also used in the field of biochemistry,pharmaceutical
chemistry,Environmental chemistry etc.,

10 MARKS :

1.With the help of a neat diagram, explain the construction and working of
dropping mercury electrode.

2. Discuss the construction and working of rotating platinum electrode.
5 MARKS:

1.Explain in detail about different types of current ?
2 MARKS :

1.What is meant by half-wave potential?

2.Write two application of polarography.

3.What is polarography

4. Principle of polarography

5. I[kovic equation

6.Residual current

7.Migration current

8.Diffusion current

9.Limiting current

166

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THE TAMIL NADU DR. M.G.R. MEDICAL UNIVERSITY

(LM 2003) MARCH 2018 Sub. Code: 2003

B.PHARM. DEGREE EXAMINATION
PCI Regulation SEMESTER —I
PAPER IIT —- PHARMACEUTICAL ANALYSIS — I

O.P. Code: 562003
Time: Three hours Maximum: 75 Marks

I. Elaborate on: Answer any TWO questions. (2 x 10 = 20)

1. Explain various types of argentimetric titrations with example.

2. With the help of a neat diagram, explain the construction and working of dropping
mercury electrode.

3. a) Describe on types of errors and methods of minimizing errors.
b) Briefly discuss on the limit test for iron.

II. Write notes on: Answer any SEVEN questions. (7x5 =35)

Briefly explain the theories of acid-base indicators.

Discuss on Diazotization titration.

Explain the general applications of conductometric titration.

Explain the principle involved in the estimation of sodium benzoate.
Describe on various steps involved in gravimetric analysis.

Write the reactions with equation for the estimation of magnesium sulphate.
Explain the principle and applications of cerimetry.

Write the construction and working of calomel electrode.
Explain on various solvents used in non aqueous titration.

OP NNM PWNS

III. Short answers on: Answer ALL questions. (10 x 2 = 20)

What is masking agent? Give an example.

Distinguish between iodimetry and iodometry.

Define titration curve.

What is meant by half-wave potential? Write its significance.
Give any two important applications of potentiometry.

What is dichrometry?

Define primary and secondary standards with example.
Classify complexometric titrations with example.

SOS PNDM PWNS

Write the IIkovic equation and explain on each term.
10, Mention the types of redox titrations.

7 ee oe ee . .
www.remixeducation.in
THE TAMIL NADU DR. M.G.R. MEDICAL UNIVERSITY

(LN 2003) SEPTEMBER 2018 Sub. Code: 2003

B.PHARM. DEGREE EXAMINATION
PCI Regulation SEMESTER — I
FIRST YEAR
PAPER IIT —- PHARMACEUTICAL ANALYSIS — I

O.P. Code: 562003
Time: Three hours Maximum: 75 Marks

I. Elaborate on: Answer any TWO questions. (2 x 10 = 20)

1. Explain the masking and de-masking agents in complexometric titrations.

2. Write the principle of redox titration and give a note on indicators used in redox
titration.

3. Write in detail about the acid base concepts and buffer solutions with examples.
II. Write notes on: Answer any SEVEN questions. (7x5 =35)

1. Describe the construction and working of dropping mercury electrode with a
diagram.

Write a note on standardization of perchloric acid.

Write a note on diazotization titrations.

Explain choice of indicators in acid — base titrations.

Give an account on the preparation and standardization of cerric ammonium
sulphate.

Write notes on pM indicators.

Explain how you will determine calcium by gravimetric analysis.

Explain neutralization curves with examples.

Write the preparation and standardization of potassium permanganate.

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SO FND

III. Short answers on: Answer ALL questions. (10 x 2 = 20)

1. What is gravimetric analysis?

2. What are chelating agents?

3. What is co-precipitation and post precipitation?

4. Werner’s co-ordination number.

5. Define precision.

6. What is the advantage of modified Volhard’s method?
7. Define accuracy.

8. What is primary standard? Explain with examples.

9. Write the different techniques of analysis.

10. What 1s permanganometry and Bromometry?

www.remixeducation.in
THE TAMIL NADU DR. M.G.R. MEDICAL UNIVERSITY

(LO 2003) MARCH 2019 Sub. Code: 2003

B.PHARM. DEGREE EXAMINATION
PCI Regulation SEMESTER — I
PAPER IT —- PHARMACEUTICAL ANALYSIS — I

O.P. Code: 562003
Time: Three hours Maximum: 75 Marks

I. Elaborate on: Answer any TWO questions. (2 x 10 = 20)

1. Explain the principle and procedure involved in the assay of calcium gluconate.

2. What is a neutralization curve? Explain the titration curves of strong acid with
strong base and weak base.

3. Explain in detail the construction and working of silver silver chloride electrode.
II. Write notes on: Answer any SEVEN questions. (7x5 =35)

Explain the principle of sulphate limit test.

Preparation and standardization of 0.1M sodium hydroxide solution.
Note on Mohr’s method.

Discuss the theory of redox titrations.

What is masking? Write its significance in analysis.

Explain the various types of currents of polarographic method.
Preparation and standardization of 0.1N sodium thiosulphate solution.
Explain the estimation of Barium sulphate by gravimetry.

Oo PNADMFYWN SE

Write the basic concept of conductometric titrations.
III. Short answers on: Answer ALL questions. (10 x 2 = 20)

Write about quantitative and qualitative analysis.

Explain the principle of back titration.

What is a primary standard? Mention one e.g. and its ideal property.
Define Amphiprotic solvents with e.g.

Write two application of polarography.

Nernst Equation.

Preparation of 0.1N Oxalic acid.

Write about personal errors.

Mention the indicator electrode used in Potentiometry.

10, Define Metal ion indicators with e.g.

Oo PNADMFYWN SE

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www.remixeducation.in
THE TAMIL NADU DR. M.G.R. MEDICAL UNIVERSITY

(LP 2003) SEPTEMBER 2019 Sub. Code: 2003

B.PHARM. DEGREE EXAMINATION
PCI Regulation SEMESTER — I
PAPER IIT —- PHARMACEUTICAL ANALYSIS — I

O.P. Code: 562003
Time: Three hours Maximum: 75 Marks

I. Elaborate on: Answer any TWO questions. (2 x 10 = 20)

1. Write the principle and different types of titration involved in Conductometric
titrations.

2. Explain the concept of iodometry and iodimetry. Give the procedure for the
Standardization of sodium thiosulphate solution using potassium iodate.

3. Discuss the principle and application of : a) Redox titration b) Polarography
II. Write notes on: Answer any SEVEN questions. (7x5 =35)

Define complex. Give theory of complexometric titrations.
Preparation and standardization of 0.05M Potassium permanganate.
Explain in detail Cerimetry.

Estimation of sodium chloride.

Discuss the construction and working of rotating platinum electrode.
Explain in detail sources of impurities in medicinal agents.

Write the principle involved in limit test for lead.

Discuss various steps involved in gravimetric analysis.

Write short notes on significant figure.

Oo PNADMFYWN SE

III. Short answers on: Answer ALL questions. (10 x 2 = 20)

What are self indicators? Give examples.

Solubility product.

What are mixed indicators?

What are primary and secondary standard substances? Give examples.
Define standard deviation and give its formula.

Explain Bronsted acid-base theory.

Differentiate between internal and external redox indicators.

Define Errors.

Co PNDM FWY

. Nernst equation.
10. Define ligands.

2fe fe fe fe fe fe 2

www.remixeducation.in
THE TAMIL NADU DR. M.G.R. MEDICAL UNIVERSITY JANUARY 2021
PAPER IT - PHARMACEUTICAL ANALYSIS — I (MARCH 2020 EXAM SESSION)
Time: Three hours Maximum: 75 Marks
I. Elaborate on: Answer any TWO questions. (2.x 10 = 20)

1. Define Diazotisation titration. Explain the basic principle, methods and applications of Diazotisation
titration.

2.What is Complexometric titration? Discuss in detail about various types of Complexometric titration with suitable
examples.

3.What are reference electrode? Describe the construction, working,advantages & disadvantages of standard
hydrogen electrode and calomel Electrode.

II. Write notes on: Answer any SEVEN questions. (7x5 =35)
1.Discuss the principle and procedure involved in Mohrs method.

2.Write a brief note on pM indicators.

3.Define Titration-Explain the choice of indicators in acid-base titration.

4.With the help of a neat neat diagram ,explain the construction and working of Roatating Platinum Electrode.
5.Define Gravimetric Analysis.Write a note on co-precipitation and post precipitation.

6.Explain the various types of solvents used in Non-aqueous titration.

7. Define Pharmaceutical analysis.What are the different methods of expressing concentration?

8.Write the sources of impurities in medicinal agents.

9.Write briefly about the preparation & standardization of potassium permanganate.

III. Short answers on: Answer ALL questions. (10 x 2 =20)
1.What is Iodimetry?

2.Define buffer with examples.

3.Define Error.Classify them.

4.Write the principle of polarography.

5.Classify redox indicator.

6.Define conductometric titration.

7.What is bromometry?

8.Define limit test

9.what do you mean by adsorption indicators? Give examples

10.Define Significant figures.

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Subject:
Pharmaceutical Analysis
Semester:
Semester
Cource:
B.Pharm

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