redox reaction involved in titration of potassium permanganate versus oxalic acid
Answers
Explanation:
The titration of potassium permanganate (KMnO4) against oxalic acid (C2H2O4) is an example of a redox titration. In close proximity to the end point, the action of the indicator is analogous to the other types of visual color titrations in oxidation-reduction (redox) titrations.
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 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
Oxidation Half reaction:- C2H42- → 2CO2 + 2e–
Overall Ionic reaction:- 2MnO4– + 16H+ + 5C2H42- → 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.
Materials Required:
Oxalic acid
Potassium permanganate solution
1.0M sulfuric acid
Chemical balance
Burette
Burette stand
Pipette
Conical flask
Funnel
Measuring flask
Weighing bottle
White tile
Burnet
Wire gauze
Apparatus Setup:
In burette – KMnO4 solution
In Conical flask – 10ml of oxalic acid + Sulfuric acid
Indicator – Self indicator (KMnO4)
End Point – Appearance of permanent pale pink colour.
Titration of Oxalic Acid with KMnO4
Titration of Oxalic Acid with KMnO4
Procedure:
(a) Preparation of 0.1N standard solution of oxalic acid:
The quantity of oxalic acid required for the 250ml of the solution having a normality of 0.1N can be calculated as follows.
Equivalent weight of oxalic acid = Molecular weight/No of electrons lost by one molecule
Equivalent weight of oxalic acid = 126/2 = 63
Strength = Normality x Equivalent weight
Strength = 1/10 x 63 = 6.3 g/l
For the preparation of 1 litre of N/10 oxalic acid solution amount of oxalic acid required = 6.3 g
Weigh an empty watch glass using a chemical balance.
Weigh 6.3g of oxalic acid accurately in the watch glass.
With the help of a funnel transfer the oxalic acid into the measuring flask.
Now wash the funnel with distilled water without removing the funnel from the flask.
Make the solution up to the marked point with distilled water and make sure the oxalic acid fully dissolved.
This solution is 0.1N standard solution of oxalic acid.