Question

KMnO4 - preparation and properties
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Answer 1

Preparation :

Potassium permanganate is prepared from pyrolusite (MnO2) ore. The preparation involves the following steps.

i) Conversion of MnO2 to potassium manganate:

Powdered ore is fused with KOH in the presence of air or oxidising agents like KNO3 or KClO3. A green coloured potassium manganate is formed.

2MnO2 + 2KOH + O2 → K2MnO4 + 2H2O

K2MnO4  = potassium manganate (Green)

ii) Oxidation of potassium manganate to potassium permanganate: Potassium manganate thus obtained can be oxidised in two ways , either by chemical oxidation or electrolytic oxidation.

Properties:

Potassium permanganate exists in the form of dark purple crystals which melts at 513 K.

It is sparingly soluble in cold water but, fairly soluble in hot water.