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Potassium Permanganate, KMnO4

Preparation on a large scale

It is prepared from the mineral pyrolusite, MnO2. The preparation involves the following steps

(i) Conversion of MnO2 into potassium manganate.

When finely powdered MnO2 is fused with KOH. K2MnO4 is obtained.


(ii) Oxidation of potassium manganate into permanganate

(a) Chemical oxidation

K2MnO4 is oxidised to KMnO4 by bubbling CO2 or Cl2 or ozone into the former.


(b) Electrolytic oxidation

 The manganate solution is electrolysed between iron electrodes. The oxygen evolved at anode converts manganate into permanganate.


Properties

KMnO4 exists as deep purple prisms. It is moderately soluble in water at room temperature and its solubility in water increases with temperature.

(i) Action of heat

When heated it decomposes to K2MnO4.


(ii) Action of conc. H­2SO4

With cold conc. H2SO4 it gives Mn2O7 which on warming decomposes to MnO2.



With hot Conc. H­2SO4 O2 is evolved


(iii) Oxidising properties

KMnO4 is a powerful oxidizing agent. The actual oxidizing action depends upon the medium i.e. acidic, basic or neutral.

(a) In neutral solution, it acts as moderate oxidizing agent.


Some oxidizing properties of KMnO4 in neutral medium are



(b) In strong alkaline solution, it is converted into


Some reactions in alkaline medium are


(c) In acidic medium, Mn+7 is converted into Mn+2


Some other reactions are

(i) 

(ii)

(iii)

(iv)

(v)

(vi)

Uses

(i) It is used in volumetric analysis for the estimation of ferrous salts, oxalates, iodides and H2O2.

(ii) It is used as oxidizing agent in the laboratory as well as in industry.

(iii) It is also used as disinfectant and germicide.

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