Calculations involving gas volumes
5 marks · HardZinc reacts with dilute sulfuric acid to produce hydrogen gas according to the equation:
State the volume, in dm³, occupied by 1 mole of hydrogen gas at rtp.
Calculate the number of moles of hydrogen produced when 3.9 g of zinc reacts completely with excess sulfuric acid.
(Relative atomic mass: Zn = 65.)
Calculate the volume, in dm³, of hydrogen gas produced at rtp from part (b).
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) 24 dm³
(b) 0.060 mol
(c) 1.44 dm³
Common mistakes: Incorrect molar volume (22.4 instead of 24); Incorrect mole calculation (not using atomic mass); Wrong units
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · States correct volume: 24 dm³ (require unit).
M1 (b) · 1 mark · Calculates moles of Zn used: moles = mass / relative atomic mass (3.9 / 65).
A1 (b) · 1 mark · Gives correct number of moles of H₂ produced: 0.060 (follow through from M1). (follow-through)
M2 (c) · 1 mark · Uses volume = moles × 24 dm³ (follow through from previous answer). (follow-through)
A2 (c) · 1 mark · Correct volume: 1.44 dm³ (allow ecf from b). (follow-through)
Worked solution
a) 1 mole of any gas at rtp occupies 24 dm³.
b) Moles of Zn = mass / relative atomic mass = 3.9 g / 65 = 0.060 mol.
1 mol Zn produces 1 mol H₂, so 0.060 mol Zn → 0.060 mol H₂.
c) Volume of H₂ = moles × molar volume = 0.060 × 24 = 1.44 dm³.