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. In the same way, when `H^(+)` ions are added to yellow solution of `CrO_(4)^(2-)` an orange solution of `Cr_(2)O_(7)^(2-)` is obtained due to interconversion.
`underset (("Orange"))underset("Dichrimate")(Cr_(2)O_(7)^(2-)) underset(H^(+))overset(OH^(-)) hArr underset("Yellow")underset("Chromate")(CrO_(4)^(2-))`