Write the preparation of sodium dichromate from chromite ore.

Dichromate are generally prepared from chromate, which in turn are obtained by the fusion of chromite ore (FeCr₂O₄) with sodium or potassium carbonate in free access of air.

The reaction with sodium carbonate occurs as follows:

4FeCr₂O₄ + 8Na₂CO₃ + 7O₂→ 8Na₂CrO₄ + 2Fe₂O₃ + 8CO₂

The yellow solution of sodium chromate is filtered and acidified with sulphuric acid to give a solution from which orange sodium dichromate, Na₂Cr₂O₇.2H₂O can be crystallised.

2Na₂CrO₄ + 2H⁺ → Na₂Cr₂O₇ + 2Na⁺ + H₂O