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 sulphuricacid,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.
A=FeCr2O4, B=Na2CrO4, C=Na2Cr2O7.2H2O, D= K2Cr2O7
Explanation:
When a chromite ore is fused with sodium carbonate, a yellow solution of sodium chromate is formed
4FeCr2O4(A) 8Na2CO3+ 7O2→ 8Na2CrO4(B) + 2Fe2O3+8CO2
When this yellow solution of sodium chromate is treated with acid, it changes to sodium dichromate
2NaCrO4 +2H+→ Na2Cr2O7 (C)+2Na+ +H2O
Sodium dichromate on treatment with KCl gives orange crystals of potassium dichromate
Na2Cr2O7 +2KCl → K2Cr2O7 (D)+2NaCl