Question

Write balanced equations for the action of acidified potassium dichromate solution on potassium iodide solution.

Answer 1

Potassium dichromate (K₂Cr₂O₇) in an acidified solution acts as a strong oxidizing agent.

The dichromate ion oxidizes iodide ions (I⁻) to iodine (I₂), and itself is reduced from Cr(VI) to Cr(III).

\[\ce{Cr2O^{2-}_7 + 14H + 6I- -> 2Cr^{3+} + 7H2O + 3I2}\]

In ionic form with potassium ions:

\[\ce{K2Cr2O7 + 14HCl + 6KI -> 2CrCl3 + 7H2O + 3I2 + 6KCl}\]