Indicate the steps in the preparation of ${K M n O}_{4}$ from pyrolusite ore.

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Solution

Potassium permanganate: $(K M n O_{4})$ can be prepared from pyrolusite $(M n O_{2})$ . The ore is fused with $K O H$ in the presence of either atmospheric oxygen or an oxidisng agent, such as $K {N O}_{3}$ or $K C l O_{4}$ to given $K_{2} M n O_{4} .$

$2 M n O_{2} + 4 K O H + O_{2} h e a t - - \to 2 K_{2} M n O_{4} (g r e e n) + 2 H_{2} O$

The green mass can be extracted with water and then oxidised either electrolytically or by passing chlorine/ozone into the solution, electrolytic oxidation

$K_{4} M n O_{4} ⇋ 2 K^{+} + M n O_{4}^{2 -}$

$H_{2} O ⇋ H^{+} + {O H}^{-}$

At anode manganate ions are oxidised to permanganate ions:

$M n O_{4}^{2 -} (g r e e n) ⇋ M n O_{4}^{-} (p u r p l e) + e^{-}$

Oxidation by chlorine:

$2 K_{2} M n O_{4} + {C l}_{2} ⇋ 2 K M n O_{4} + 2 K C l$

$2 M n O_{4}^{2 -} + {C l}_{2} ⇋ 2 M n O_{4} + 2 {C l}^{-}$

Oxidation by ozone:

$2 K_{2} M n O_{4} + O_{3} + H_{2} O \to 2 K M n O_{4} + 2 K O H + O_{2}$

$2 M n O_{4}^{2 -} + O_{3} + H_{2} O \to 2 M n O_{4}^{2 -} + 2 O H^{-} + O_{2}$

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