An impure sample of zinc weighing 3.25 g is treated with excess dilute sulfuric acid, yielding 896 mL of hydrogen gas at STP. The percentage purity of the zinc sample is: (Given: Molar mass of Zn = 65 g mol ⁻¹ , Molar volume of a gas at STP = 22.4 L mol ⁻¹ )

Step-by-step solution

The balanced chemical equation for the reaction is: Zn + H ₂ SO ₄ ZnSO ₄ + H ₂ Moles of H ₂ gas evolved = 896 10⁻³ L 22.4 L mol ⁻¹ = 0.04 mol From the stoichiometry, 1 mole of Zn produces 1 mole of H ₂ . Moles of pure Zn reacted = 0.04 mol Mass of pure Zn = 0.04 mol 65 g mol ⁻¹ = 2.6 g Percentage purity = Mass of pure Zn Total mass of sample 100 Percentage purity = 2.6 3.25 100 = 80 % Answer: 80 %