When a chromite ore (A) is fused with sodium carbonate in free excess of air and the product is dissolved in water, a yellow solution of compound (B) is obtained. After treatment of this yellow solution with sulphuric acid, compound (C ) can be crystallised from the solution. When compound (C ) is treated with KCl, orange crystals of compound (D) crystallise out. Identify A to D and also explain the reactions.

Explanation

(i)`underset("ore")underset("Chromite")(4FeO.Cr_(2)O_(3))+8Na_(2)CO_(3)+7O_(2)rarrunderset(("yellow"))underset(("A"))underset("chromate")underset("sodium")(8Na_(2)CrO_(4))+2Fe_(2)O_(3)+8CO_(2)`
(ii) `underset("chromate")underset("Sodium")(2Na_(2)CrO_(4))+H_(2)SO_(4)rarr underset("dichromate")underset("Sodium")(Na_(2)Cr_(2)O_(7))+Na_(2)SO_(4)+H_(2)O`
(iii) `Na_(2)Cr_(2)O_(7)+2KCl rarrunderset("Orange Crystal")underset(("C"))underset("dichromate")underset("Potassium")(K_(2)Cr_(2)O_(7))+2NaCl`
A = `Na_(2)CrO_(4)` (Sodium Chromate), B = `Na_(2)Cr_(2)O_(7)` (Sodium dichromate)
C = `K_(2)Cr_(2)O_(7)` (Potassium dichromate)