oxalic acid KMnO4

1. SHREE MALLIKARJUN COLLEGE CLASS:FYBSC
SAFETY: Refer to MSDS of oxalic acid, potassium permanganate, sulphuric acid, sodium oxalate
Dr. Mithil S. Fal Desai
Aim: Estimation of oxalic acid by titrating with KMnO4.
Chemicals: Oxalic acid, potassium permanganate, sulphuric acid, sodium oxalate.
Apparatus: Standard volumetric flask, pipette, burette, conical flask, beakers, funnel and glass rod.
Theory: The titration of potassium permanganate (KMnO4) against oxalic acid (C2H2O4) is an example of
a redox reaction. In this titration, Mn is reducedand C is oxidized from KMnO4 and (COOH)2,respectively.
Initially, KMnO4 reacts with oxalate ions to form Mn2+
, K+
, CO2, and water,which result in a colourless
solution. After complete consumption of oxalate ions at the endpoint, an extra drop of KMnO4 turns the
solution pink which indicates complete oxidation of oxalate ions. As the reaction is sluggish at room
temperature oxalic acid along with sulphuric acid is heated to about 60 °C before the titration.
The aqueous solution of KMnO4 needs to be standardized using sodium oxalate.
Reaction:
2KMnO4 + 5H2C2O4 + 3H2SO4  2MnSO4 + K2SO4 + 10CO2 + 8H2O
(MnO4)-
+ 8H+
+ 5 e-
 Mn2+
+ 4H2O X 2 (Reduction)
(COO)2
2-
 CO2 + 2 e-
X 5 (Oxidation)
2(MnO4)-
+ 5(COO)2
2-
+ 16H+
 2Mn2+
+ 10CO2 + 8H2O
Procedure:
i) Preparation of 0.01N KMnO4 (500 mL) [molecular weight check on the chemical container], calculate
ii) Preparation of 2N H2SO4 (250 mL) [Laboratory normality 36 N],calculate
iii) Preparation of 0.01N Na2C2O4 (500 mL) [molecular weight check on the chemical container], calculate
iv) Standardization of KMnO4
Rinse the clean burette with a minimum quantity of KMnO4 and fill it appropriately. Pipette out 10 mL of
0.01 N sodium oxalate solution in a clean conical flask. Add about 20 mL of 2N H2SO4. Heat the solution
in a flask to about 60 °C. Titrate it against KMnO4, until light pink colour permanently develops in the
flask. Repeat the titration to get constant readings.
v) Estimation of oxalic acid
Pipette out 10 mL of given oxalic acid solution in a clean conical flask. . Add about 20 mL of 2N H2SO4.
Heat the solution in a flask to about 60 °C. Titrate it against KMnO4, until light pink colour permanently
develops in the flask. Repeat the titration to get constant readings.
Results:
i) Amount of oxalic acid in 100 mL___g.
Further reading (available in library)
1) Experiments in Applied Chemistry, S. Rattan, S. K Kataria and Sons.
2) Vogel’s textbook of quantitative chemical analysis, J. Mendham, R. C. Denney,J. D. Barns,M. Thomas,
B. Sivasankar, Pearson India Education, 6th
Edition.