Question

How do you prepare:

Na₂Cr₂O₇ from Na₂CrO₄?

Answer 1

Na₂Cr₂O₇ can be prepared from Na₂CrO₄ in the following way:
For the preparation of sodium dichromate, the yellow solution of sodium chromate is acidified with sulphuric acid to give a solution from which orange sodium dichromate, Na₂Cr₂O₇.2H₂O can be crystallised.
Balanced equation for above reactions is as follows:

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