Potassium dichromate, K₂Cr₂O₇

Preparation of Potassium dichromate:

It is prepared by fusion of chromate ore (FeCr2O4) with sodium carbonate in excess of air.

Na₂CrO₄ produced in the above reaction is then acidified to get sodium dichromate, Na₂Cr₂O₇

The solution of sodium dichromate treated with potassium chloride to get the final product, K₂Cr₂O₇.

Structures of CrO₄^2‒ and Cr₂O₇^2‒ ions:

Uses of Potassium dichromate:

Potassium dichromate is used as a primary standard in volumetric analysis and as an oxidizing agent. In acidic medium, the oxidation state of Cr changes from + 6 in Cr₂O₇^2‒  to + 3 in Cr³⁺.