CHEMISTRY · Subjective · A Level · Chemistry · Oxidation, reduction and redox reactions · Oxidation, reduction and redox reactions
Problem
A 3.0 g sample containing Fe3O4 , Fe2O3 and an inert impure substance is treated with excess of KI solution in 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 11.0 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+ . Calculate the percentage of Fe2O3 and Fe3O4 in the original sample.