Describe the preparation of potassium permanganate. How does the acidified permanganate solution react with (i) iron(II) ions (ii) SO₂ and (iii) oxalic acid?

Write the ionic equations for the reactions.

Potassium permanganate can be prepared from MnO₂. It can be done by fusing the ore with KOH in presence of an oxidizing agent like atmospheric oxygen/KNO₃ etc to give green coloured K₂MnO₄ as the product.

2MnO₂ + 4KOH + O₂ → 2K₂MnO₄ + 2H₂O

The Product K₂MnO₄ is extracted with water and then oxidised by passing ozone/chlorine into the solution or electrolytically.

Electrolytic oxidation:

At Anode, manganite ions are oxidized to permanganate ons.

(i) Acidified KMnO₄ solution oxidizes Fe(II) ions to Fe(III) ions and water as product

MnO₄^- + 8H⁺ + 5e^- → Mn²⁺ + 4H₂O

Fe²⁺→ Fe³⁺+ e^- } x5

Overall: MnO₄^- + 8H⁺ + 5Fe²⁺ → Mn²⁺ + 4H₂O + 5Fe³⁺

(ii) Acidified potassium permanganate oxidizes SO₂ to sulphuric acid as follows:

MnO₄^- + 6H⁺ + 5e^- → Mn²⁺ + 3H₂O } x2

2H₂O + 2SO₂ + O₂→ 4H⁺ + 2SO₄^2- + 2e^-} x5

Overall: MnO₄^- + 4H₂O + 10SO₂ + 5O₂→ 8H⁺ + 10SO₄^2- + 2H⁺

(iii) Acidified potassium permanganate oxidizes oxalic acid to carbon dioxide

MnO₄^- + 8H⁺ + 5e^- → Mn²⁺ + 4H₂O} x2

C₂O₄^2-→ 2CO₂ + 2e^- } x5

Overall: 2MnO₄^- + 16H⁺+ 5C₂O₄^2- → 2Mn²⁺ + 10CO₂+ 8H₂O