Question

4.35 g of a sample of pyrolusite (MnO₂) when heated with conc. HCI gave chlorine. The chlorine when passed through potassium iodide solution liberated 6.35 g of iodine. The percentage purity of the pyrolusite sample is

(a) 40

(b) 50

(c) 60

(d) 70

Answer 1

Correct option is (b) 50

MnO₂ + 4HCI → 2MnCl₂ + Cl₂ + 2H₂O; 

2KI + Cl₂ → 2KCl + I₂

Moles of 12 liberated moles of Cl₂ = moles of MnO₂ = \(\frac{6.35}{254}\)

Weight of pure MnO₂ = \(\frac{6.35 \times 87}{254}\) = 2.175

% Purity of MnO₂ = \(\frac{2.175 \times 100}{4.35} \) = 50