Question

Describe the preparation of potassium permanganate. How does the acidified permanganate solution react with SO₂? Write the ionic equation for the reaction.

Indicate the steps in the preparation of KMnO₄ from pyrolusite ore.

Answer 1

Potassium permanganate can be made by the following methods –

It is produced industrially by the electrolytic oxidation of manganate (VI), followed by the alkaline oxidative fusion of MnO₂.

\[\ce{MnO2 ->[Fused with KOH, oxidised with air or KNO3] \underset{manganate ion}{MnO^{2-}_4}}\]

\[\ce{\underset{manganate}{MnO^{2-}_4} ->[Electrolytic oxidation in alkaline solution] \underset{permanganate ion}{MnO^-_4}}\]

The chemical reactions of acidic potassium permanganate are as follows –

\[\ce{2MnO^-4 + 2H2O + 5SO2 -> 2Mn^{2+} + 4H^+ + 5SO^{2-}_4}\]

Answer 2

\[\ce{2MnO2 + 4KOH + O2 ->[\Delta] 2K2MnO4 + 2H2O}\]

\[\ce{3MnO^2-_4 + 4H+ -> 2MnO^-_4 + MnO2 + 2H2O}\]