What color change indicates the oxidation of an orange acidified dichromate solution?

The oxidation of an orange acidified dichromate solution is indicated by a color change to green. This color change occurs because the dichromate ion (Cr₂O₇²⁻), which is orange in color, is reduced to chromium(III) ions (Cr³⁺), which appear green in solution.

In an acidic environment, the dichromate ions are effective oxidizing agents, meaning they can accept electrons from other species and undergo reductions themselves. During this redox reaction, the orange color fades as the dichromate is consumed, and the resulting chromium(III) ions impart a green color to the solution. This transition from orange to green is a clear visual indicator of the oxidation process taking place.

Understanding this color change is essential in practical applications, such as in titrations or redox reactions, where the observation of color can serve as a qualitative measure of the reaction's progression.