Titration of KMnO₄ vs Oxalic Acid || Acid Redox Titration || DrRajnishChem || Class 12 Chemistry

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Titration of KMnO₄ vs Oxalic Acid || Acid Redox Titration || DrRajnishChem || Class 12 Chemistry

Aim:
To determine the strength of potassium permanganate by titrating it against the standard solution of 0.1M oxalic acid.

Theory:
Potassium permanganate is a strong oxidising agent and in the presence of sulfuric acid it acts as a powerful oxidising agent. In acidic medium the oxidising ability of KMnO4 is represented by the following equation.

In acidic solution,

MnO4– + 8H+ + 5e– → Mn2+ + 4H2O

Solution containing MnO4– ions are purple in colour and the solution containing Mn2+ ions are colourless and hence permanganate solution is decolourised when added to a solution of a reducing agent. The moment there is an excess of potassium permanganate present the solution becomes purple. Thus, KMnO4 serves as self indicator in acidic solution.

Potassium permanganate is standardized against pure oxalic acid. It involves a redox reaction. Oxalic acid is oxidised to carbon dioxide by KMnO4, which itself gets reduced to MnSO4. Oxalic acid reacts with potassium permanganate in the following way.

The chemical reaction at room temperature is given below.

Reduction Half reaction:- 2KMnO4 + 3H2SO4 → K2SO4 + 2MnSO4 + 3H2O + 5[O]

Oxidation Half reaction:- 5(COOH)2 + 5[O] → 5H2O + 10CO2↑

The overall reaction takes place in the process is

Overall reaction:- 2KMnO4 + 3H2SO4 + 5(COOH)2 → K2SO4 + 2MnSO4 + 8H2O + 10CO2↑

The ionic equation involved in the process is given below.

Reduction Half reaction:- [MnO4– + 8H+ + 5e– → Mn2+ + 4H2O] x 2

Oxidation Half reaction:- [C2O42- → 2CO2 + 2e–] x 5

Overall Ionic reaction:- 2MnO4– + 16H+ + 5C2O42- → 2Mn2+ + 10CO2 + 8H2O

This titration cannot be carried out in the presence of acids like nitric acid or hydrochloric acid because itself is an oxidising agent. So hydrochloric acid chemically reacts with KMnO4 solution forming chlorine which is also an oxidising agent.


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