Views: 11
Examples Of Redox Titration
Thus, it can be understood that redox titrations involve a transfer of electrons between the given analyte and the titrant.
An example of a redox titration is the titration of potassium permanganate (KMnO4) against oxalic acid (C2H2O4).
Preparation of redox solutions
In this experiment, potassium permanganate acts as a powerful oxidising agent. Although KMnO4 acts as an oxidising agent in alkaline medium also, for quantitative analysis mostly acidic medium is used. The oxidising action of KMnO4 in the acidic medium can be represented by the following equation:
MnO4 + 8H+ + 5e– → Mn2+ +4H2O
The acid used in this titration is dilute sulphuric acid. Nitric acid is not used as it is itself an oxidising agent and hydrochloric acid is usually avoided because it reacts with KMnO4 according to the equation given below to produce chlorine and chlorine which is also an oxidising agent in the aqueous solution.
2KMnO4 + 16 HCl → 2KCl + 2 MnCl2 + 5Cl2 + 8 H2O
Oxalic acid acts as a reducing agent, it can be titrated against potassium permanganate in the acidic medium according to the following equation:
Reactions of oxalic acid
- Chemical equations
Reduction half reaction :
2KMnO4 + 3H2 SO4 → K2 SO4 + 2MnSO4 + 3H2O + 5 [O]
Oxidation half reaction :
H2C2 O4 + [O] → 2CO2 + H2 O] × 5
2KMnO4 + 3H2SO4 + 5H2C2O4 → K2 SO4 + 2MnSO4 + 8H2O + 10 CO2
- Ionic equation
Reduction half reaction :
MnO4 – + 5e– + 8H+ → Mn2+ + 4H2O] × 2
Oxidation half reaction :
C2O4 – → 2CO2 + 2e– ] × 5
2 MnO4 – + 5C2O4 2– + 16H+ → 2Mn2+ + 10CO2 + 8H2O
In these equations, MnO4 – is reduced to Mn2+ and C2O4 2– is oxidised to CO2 . The oxidation number of carbon in C2O4 2– changes from +3 to +4. In these titrations, potassium permanganate acts as a self-indicator.
Initially colour of potassium permanganate is discharged due to its reduction by oxalic acid.
After complete consumption of oxalate ions, the end point is indicated by the appearance of a light pink colour produced by the addition of a little excess of unreacted potassium permanganate.
Further, during the titration of oxalic acid against potassium permanganate, warming of oxalic acid solution (50°–60°C) along with dilute H2SO4 is required. This is essential because the reaction takes place at higher temperature. During the titration, first manganous sulphate is formed which acts as a catalyst for the reduction of KMnO4 by oxalic acid. Therefore, in the beginning the reaction rate is slow and as the reaction proceeds, the rate of the reaction increases.