Question:
When an orange solution containing Cr2O72– ion is treated with an alkali, a yellow solution is formed and when H+ ions are added to a yellow solution, an orange solution is obtained. Explain why does this happen?
Solution:
When Cr2O72–is treated with an alkali:
(orange) Cr2O72–+ OH-→ 2CrO42-(yellow)
When the yellow solution is treated with an acid, we get back the orange solution:
(yellow)2CrO42- +2H+→Cr2O72–(orange)+ H2O