Question

Describe with chemical equations, what happens when K₂Cr₂O₇ reacts with an acidified solution of Kl?

Answer 1

When acidified potassium dichromate (K₂Cr₂O₇) reacts with an acidified solution of potassium iodide (KI), iodine (I₂) is liberated. In this redox reaction:

Dichromate ion \[\ce{(Cr2O^{2-}_7)}\] is reduced to Cr³⁺

Iodide ion (I⁻) is oxidised to Iodine (I₂)

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

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