Question

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.

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

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

The chemical reactions of acidic potassium permanganate with SO₂ are as follows –

\[\ce{2MnO4 + 2H2O + 5SO2 -> 2Mn^{2+} + 4H^+ + 5SO^{2-}_4}\]

Answer 2

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

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