Chemistry - Redox Reactions Question with Solution | TestHub
A 3.0 g sample containing Fe₃O₄, Fe₂O₃ and an inert impure substance is treated with excess of KI solution in the presence of dilute H₂SO₄. The entire iron is converted to Fe²⁺ along with the liberation of iodine. The resulting solution is diluted to 100 ml. A 20 ml of dilute solution requires 11.2 ml of 0.5 M - Na₂S₂O₃ solution to reduce the iodine present. A 50 ml of the diluted solution, after complete extraction of iodine, requires 12.80 ml of 0.25 M - KMnO₄ solution in dilute H₂SO₄ medium for the oxidation of Fe²⁺. The percentage of Fe₂O₃ in the original sample is
Answer:
Solution:
I₂ in 20 ml aliquot = (11.2×0.5)/2 = 2.8 mmol, so total I₂ = 14 mmol; only Fe³⁺ liberates I₂ (2Fe³⁺ : I₂), hence total Fe³⁺ = 28 mmol. Total Fe²⁺ in 50 ml = 5×12.80×0.25 = 16 mmol, so total Fe = 32 mmol. Let a = mmol Fe₃O₄, b = mmol Fe₂O₃: a+b = 14 (I₂), 3a+2b = 32 (total Fe), giving a = 4, b = 10 mmol. Mass Fe₂O₃ = 10×160 = 1600 mg = 1.6 g; % = 1.6/3.0×100 = 53.3%. Ans 0053.
