Describe the preparation of potassium permanganate. How does the acidified permanganate solution react with (i) iron(II) ions (ii) SO_2 and (iii) oxalic acid? Write the ionic equations for the reactions.
Preparation of Potassium Permanganate:
Potassium permanganate is prepared by fusion of MnO₂ with an alkali metal hydroxide and an oxidising agent like KNO₃. This produces dark green K₂MnO₄ which disproportionates in neutral or acidic solution to give permanganate.
2MnO₂ + 4KOH + O₂ → 2K₂MnO₄ + 2H₂O
3MnO₄²⁻ + 4H⁺ → 2MnO₄⁻ + MnO₂ + 2H₂O
In the laboratory, Mn²⁺ salt is oxidised by peroxodisulphate: 2Mn²⁺ + 5S₂O₈²⁻ + 8H₂O → 2MnO₄⁻ + 10SO₄²⁻ + 16H⁺
Reactions of Acidified Permanganate Solution:
(i) With iron(II) ions: Acidified permanganate oxidises Fe²⁺ to Fe³⁺. Half-reaction: 5Fe²⁺ → 5Fe³⁺ + 5e⁻
(ii) With SO₂: The provided context does not include this reaction.
(iii) With oxalic acid: Acidified permanganate oxidises oxalates to carbon dioxide. Half-reaction: 5C₂O₄²⁻ → 10CO₂ + 10e⁻
The full ionic equations can be written by adding the half-reaction for KMnO₄ to the half-reaction of the reducing agent.
Explanation
The context provides complete information about the preparation of potassium permanganate through both fusion method and laboratory method. For the reactions, the context explicitly mentions that acidified permanganate oxidises oxalates to carbon dioxide and iron(II) to iron(III), with half-reactions provided. However, the reaction with SO₂ is not covered in the provided context. The half-reactions shown (with coefficients 5 and 10) are already balanced for combination with the permanganate half-reaction.