When 20 g of an impure iron sample reacts with excess HCl, 6.72 L of hydrogen gas (STP) is released. What is the mass fraction of pure iron in the sample?
- 84%
- 56%
- 75%
- 90%
📝 Detailed explanation
Fe + 2HCl → FeCl₂ + H₂.n(H₂) = 6.72 / 22.4 = 0.3 mol.
n(Fe) = 0.3 mol.
Mass pure Fe = 0.3 * 56 = 16.8 g.
Mass fraction = 16.8 / 20 = 0.84 or 84%.