Question 16

Describe the preparation of potassium permanganate. How does the acidifiedpermanganate solution react with

(i) iron

(II) ions 

(ii) SO2 and

(iii) oxalic acid?

Write the ionic equations for the reactions.

Answer

Potassium permanganate can be prepared from pyrolusite (MnO2). The ore is fused with KOH in the presence of either atmospheric oxygen or an oxidising agent, such as KNO3or KClO4, to give K2MnO4.

 

The green mass can be extracted with water and then oxidized either electrolytically or by passing chlorine/ozone into the solution.

Electrolytic oxidation

K2MnO4   ↔    2K+   +    MnO2-4

H2O     ↔   H+   +  OH-

At anode, manganate ions are oxidized to permanganate ions.

MnO2-4       ↔     MnO-4    +   e-

Green                 Purple 

Oxidation by chlorine

 

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