Question

Explain how the colour of K₂Cr₂O₇ solution depends on pH of the solution.

Answer 1

The colour of potassium dichromate solution depends on the pH due to equilibrium between chromate and dichromate ions. In acidic medium, dichromate ions \[\ce{(Cr2O^{2-}7)}\] predominate and the solution is orange, while in alkaline medium, chromate ions \[\ce{(CrO^{2-}4)}\] predominate and the solution turns yellow.