Question

Mass of magnesium required to produce 220 mL of hydrogen gas at STP on reaction with excess of dil. HCl is

Given: Molar mass of Mg is 24 g mol$^{-1}$.

• A. 236 mg
• B. 235.7 g
• C. 0.24 mg
• D. 2.444 g

Answer 1

Answer: (A)

236 mg

Answer 2

1. Convert Volume:
    220 mL = 0.22 L

2. Calculate Moles of H₂:
    At STP, 1 mole of gas = 22.4 L
    Moles of H₂ = 0.22 L / 22.4 L/mol ≈ 0.00982 mol

3. Find Mass of Mg:
    Reaction: Mg + 2HCl → MgCl₂ + H₂
    (Mole ratio Mg : H₂ = 1:1)
    Mass of Mg = 0.00982 mol × 24 g/mol ≈ 0.2357 g ≈ 236 mg