Chemical properties of K₂Cr₂O₇

i. Oxidation of $\mathrm{I^-}$ from an aqueous solution of KI by acidified $\mathrm{K_2Cr_2O_7}$ gives $\mathrm{I_2}$. Potassium dichromate is reduced to chromic sulphate. Liberated $\mathrm{I_2}$ turns the solution brown.

$\mathrm{K_2Cr_2O_7 + 6KI + 7H_2SO_4 \longrightarrow 4K_2SO_4 + Cr_2(SO_4)_3 + 7H_2O + 3I_2}$ …