CBSE Class 12 Chemistry Notes: d and f Block Elements – Potassium Permanganate

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. H_­2SO₄

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

With hot Conc. H_­2SO₄ 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.

Class 12 Chemistry d and f Block Elements All Topic Notes Class 12 Chemistry All Chapters Notes