When orange solution containing `Cr_(2)O_(7)^(2-)` ion is treated with an alkali, a yellow solution is formed and when `H^(+)` ions are added to yellow solution, an orange solution is obtained. Explain why does this happen?

Explanation

When orange solution containing `Cr_(2)O_(7)^(2-)` ion is treated with an alkali, a yellow solution of `CrO_(4)^(2-)` is obtained. On the same way, `undersetunderset(("orange"))("Dischromate")(Cr_(2)O_(7)^(2-))underset(H^(+))overset(OH^(-))rarrundersetunderset(("yellow"))("Chromate")(CrO_(4)^(2-))`
when `H^(+)` ions are added to yellow solution, an orange solution is obtained due to interconversion.