Oxidation Reduction

TITRIMETRIC METHODS
REDOX TITRATIONS
DR.MAHWISH FARRUKH
OXIDATION-REDUCTION TITRATIONS
It is a chemical method of quantity analysis which involve change in valence of the

reacting substances and considered as a basis for volumetric determination.
OXIDATION
It is defined as a process of:

 Addition of oxygen. Eg:
 Removal of hydrogen. Eg:
 Loss of electron or ions. Eg:
REDUCTION
It is defined as:
 The addition of hydrogen. Eg:
 Removal of oxygen. Eg:
 Gain of electron by atoms or ions. Eg:
Oxidation and REDUCTION reaction
 Oxidation and reduction reactions occur at the same time i.e. when one
substance is oxidized and the other substance is reduced and vice versa.
 A reagent which undergoes reduction by oxidizing the other is called oxidizing

agent and a standard solution of the oxidizing agent is being used for titration.
 The chief oxidizing agents used in volumetric analysis are:
“Potassium permanganate, Potassium dichromate, ferric ammonium sulphate,
Potassium bromate etc.
 A reagent which undergoes oxidation by reducing the other is called
reducing agent.
 The important reducing agents are: sodium thiosulphate, ferrous ammonium
sulphate, oxalic acid, sodium oxalate etc.
 In redox titration, the estimations generally done by the following methods:
I. Potassium permanganate KMnO4 method.
II. Potassium dichromate K2Cr2O7 method.
III. Iodine method( Iodometry and Iodimetry)
POTASSIUM PERMANGANATE KMnO4
METHOD
 This method is also called “PERMANGANATOMETRY”

 In this, titrant is KMnO4 and titrand is oxalic acid solution.
 First prepare 0.1 N KMnO4 solutions .
PREPARATION OF 0.1N KMnO4
The use of KMnO4 is an oxidizing agent in acid solution depend upon the reaction.
PROCEDURE:
 Prepare 1L standard solution of oxalic acid by dissolving xg of oxalic acid in water.

 Pipette out about 20ml oxalic acid solution into the conical flask and add 20ml
H2SO4 (dilute) and then warm about 70C.
 Run KMnO4 approx. from the burette very slowly and shake the flask after each
addition. (avoid addition of large amount of KMnO4 at a time as it forms brown
precipitates of hydrate MnO4)
Continued on Next Slide
 End point is reached when a pink colour appears for about 30sec upon shaking the
flask.
 Note the burette reading and repeat the titration to get at least 2 concordant.
 Calculate the exact Normality of KMnO4 by using formula
 N1V1=N2V2
Note: H2SO4 are used because they are stable but here HCl is not used because it
would be oxidized to chlorine by permanganate to form Cl2(g) so would not be stable
to react with the oxalic acid solution.
INDICATOR USED IN THIS TITRATION: KMnO4 itself used as an indicator because of its
bright color.
POTASSIUM DICHROMATE
K2Cr2O7 METHOD
This method is also called “Dichromatometry”.

In this method, K2Cr2O7 is used as a titrant and also used as a primary substance .
It is only used in acidic medium so Cr2O7 ion will reduce to Cr+3 which is green in
colour.
PREPARATION OF POTASSIUM DICHROMATE

In this, Iron(II) salt is used as titrand.
PROCEDURE:
 Prepare standard solution containing Fe+2 in a conical flask.
 Add H2SO4 to provide the acidic medium.
 Run K2Cr2O7 approx. from the burette very slowly and shake the flask after each
addition.
 End point is determined by using the indicator when green color appears.
 Note the burette reading and repeat the titration to get at least 2 concordant.
INDICATORS USED IN THIS TITRATION:

 Potassium ferric cyanide.
 Diphenylamine sulphonate.
TITRATIONS INVOLVING IODINE
IODOMETRY:
 In this, liberated iodine is used for titration.
 The method which involves in reducing the oxidizing agent with excess of
potassium iodide whereby an equivalent amount of iodine is produced which is
titrated with a standard solution of sodium thiosulphate is known as iodometry
 The iodometric methods of analysis incorporating the use of iodine are based on
oxidation-reduction reactions .The reversible reaction i-e: is utilized indirectly in
the analysis of oxidizing agents like ferric cupric salts.
IODIMETRY:
 The method in which the reversible reaction i-e is utilized in the analysis of the
reducing agents like thiosulphates and arsenites by direct titration with a standard
solution of iodine is known as iodimetry.
 The indicator used consists of starch solution in which the presence of 1 part of
iodine in several million parts of solution can be detected . Starch solution on
interaction with iodine or iodide ion produces an intense blue color which can be
discharged when iodine is reduced with Na2S2O3 or any other reducing agent.
APPLICATIONS OF REDOX TITRATION
 One of the most important applications of redox titration is in both public health
and environmental analysis is the determination of dissolved oxygen.
 Redox titration is applied in evaluating the chlorination of public water supplies.
 The earliest Redox titration took advantage of the oxidizing power of chlorine. In
1787, Claude Berthollet introduced a method for the quantitative analysis of
chlorine water (a mixture of Cl2, HCl, and HOCl) based on its ability to oxidize
indigo, a dye that is colorless in its oxidized state. In 1814, Joseph Gay-Lussac
developed a similar method for determining chlorine in bleaching powder. In both
methods the end point is a change in color. Before the equivalence point the
solution is colorless due to the oxidation of indigo. After the equivalence point,
however, unreacted indigo imparts a permanent color to the solution.
Redox reactions are important in
 Purifying metals like Al,Na,Li etc.

 Producing gases like chlorine, oxygen and hydrogen etc.
 Electroplating metals
 Protecting metals from corrosion.
 Electrical productions like batteries, cells etc.
THANK YOU

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TITRIMETRIC METHODS

It is a chemical method of quantity analysis which involve change in valence of the

It is defined as a process of:

 A reagent which undergoes reduction by oxidizing the other is called oxidizing

 This method is also called “PERMANGANATOMETRY”

 Prepare 1L standard solution of oxalic acid by dissolving xg of oxalic acid in water.

This method is also called “Dichromatometry”.

PREPARATION OF POTASSIUM DICHROMATE

INDICATORS USED IN THIS TITRATION:

 Purifying metals like Al,Na,Li etc.

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