Q.How many moles of $I_2$ are liberated when 1 mole of potassium dichromate react with potassium iodide ?

Potassium dichromate is a powerful oxidising agent in ACIDIC medium: Cr₂O₇²⁻ + 14H⁺ + 6e⁻ → 2Cr³⁺ + 7H₂O, a change from Cr⁶⁺ to Cr³⁺. Worked examples: (i) oxidises Fe²⁺ to Fe³⁺ (basis of a volumetric iron estimation); (ii) oxidises I⁻ to I₂ (basis of an iodometric determination of dichromate, titrated against thiosulphate); (iii) oxidises S²⁻ to S (milky turbidity); (iv) oxidises SO₂ to SO₄²⁻; (v) oxidises Sn²⁺ to Sn⁴⁺; (vi) with excess reagent, oxidises ethanol all the way to acetic acid (CH₃COOH) -- 2K₂Cr₂O₇ + 8H₂SO₄ + 3CH₃CH₂OH → 2K₂SO₄ + 2Cr₂(SO₄)₃ + 3CH₃COOH + 11H₂O. …