Chemistry - Stoichiometry Question with Solution | TestHub
Chromium exists as FeCr₂O₄ in the nature and it contains Fe₀.₉₅O₁.₀₀ as an impurity. To obtain pure chromium from FeCr₂O₄, the ore is fused with KOH and oxygen is passed through the mixture when K₂CrO₄ and Fe₂O₃ are produced. A quantity of 2 g of ore required 280 ml of O₂ at 0°C and 1 atm for complete oxidation of ore. K₂CrO₄ is then precipitated as BaCrO₄ after addition of Barium salt. To the remaining solution, 10 ml of 1 M - K₄Fe(CN)₆ is added when Fe³⁺ ions reacts with it to form KFe[Fe(CN)₆], after called 'Prussian Blue'. To determine excess of K₄Fe(CN)₆ in solution, 6 ml of 0.4 N - Fe²⁺ is added when all the K₄Fe(CN)₆ is precipitated as K₂Fe[Fe(CN)₆]. (Fe = 56)
What per cent of total iron present in the ore is in +2 state?
Options:
Answer:
Solution:
From Q22, FeCr₂O₄ = 1.8616 g = 8.31 mmol (all Fe²⁺) and Fe₀.₉₅O = 2 mmol, in which charge balance gives Fe²⁺ = 0.85 per formula unit = 1.7 mmol and Fe³⁺ = 0.2 mmol. Fe²⁺ = 8.31 + 1.7 = 10.01 mmol; total Fe = 10.21 mmol. Fraction = 10.01/10.21 × 100 ≈ 98%, closest to 97.73%, matching (b).
