$1)$ Indicate the steps in the preparation of :
$A)$ $K_{2} C r_{2} O_{7}$ from chromite ore

$B)$ $K M n O_{4}$ from pyrolusite ore

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Solution

$A)$ Potassium dichromate $(K_{2} C r_{2} O_{7})$ is

prepared from chromite ore $(F e C r_{2} O_{4})$ by the following steps:

Step 1: Preparation of sodium chromate from chromite ore

$4 F e C r_{2} O_{4} + 8 N a_{2} C O_{3} + 7 O_{2} \to 8 N a_{2} C r O_{4} + 2 F e_{2} O_{3} + 8 C O_{2}$

Step 2: Conversion of sodium chromate into sodium dichromate

$2 N a_{2} C r O_{4} + C o n c . H_{2} S O_{4} \to N a_{2} C r_{2} O_{7} + 2 N a^{+} + H_{2} O$

Step 3: Conversion of sodium dichromate to potassium dichromate

$N a_{2} C r_{2} O_{7} + 2 K C l \to K_{2} C r_{2} O_{7} + 2 N a C l$

Potassium chloride being less soluble than sodium chloride is obtained in the form of orange-coloured crystals and can be removed by filtration.

$B)$ Convert pyrolusite to $K_{2} M n O_{4}$

Potassium permanganate can be prepared from the fusion of pyrolusite ore $(M n O_{2})$ with an alkali metal hydroxide and an oxidising agent (like $K N O_{3})$ .

This gives dark green $K_{2} M n O_{4} .$

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

Conversion of $K_{2} M n O_{4}$ to $K M n O_{4}$

$K_{2} M n O_{4}$ disproportionate in acidic or neutral medium to give permanganate.

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

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Similar questions

Indicate the steps in the preparation of:

(i) K2Cr2O7 from chromite ore.

(ii) KMnO4 from pyrolusite ore.

K_{2} C r_{2} O_{7}

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Indicate the steps in the preparation of:

(i) K2Cr2O7from chromite ore.

(ii) KMnO4from pyrolusite ore.

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