Explain the manufacture of potassium dichromate from chromite ore $(F e C r_{2} O_{4})$ .

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Solution

Potassium dichromate ( $K_{2} C r_{2} O_{7}$ ) is prepared from chromite ore $F e C r_{2} O_{4}$ . The chromite ore is fused with sodium or potassium carbonate in free access of air.
$4 F e C r_{2} O_{4} + 8 N a_{2} C O_{3} + 7 O_{2} \to 8 N a_{2} C r O_{4} + 2 F e O_{3} + 8 C O_{2}$

The yellow solution of sodium chromate is filtered and acidified with sulfuric acid to give a solution from which orange sodium dichromate , $N a_{2} C r_{2} O_{7} . 2 H_{2} O$ can be crystallized.
$2 N a_{2} C r O_{4} + 2 H^{+} \to N a_{2} C r_{2} O_{7} + 2 N a + H_{2} O$

Sodium dichromate is more soluble than potassium dichromate. Hence, sodium dichromate when fused with KCl forms orange crystals of potassium dichromate.
$N a_{2} C r_{2} O_{7} + 2 K C l \to K_{2} C r_{2} O_{7} + 2 N a C l$

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