Using the molar volume in calculations with chemical equations
3 marks · EasyTo prepare hydrogen in the laboratory, zinc reacts with excess dilute sulfuric acid according to this equation:
A student adds 13.0 g of zinc (Ar: Zn = 65) to excess sulfuric acid.
Calculate the number of moles of zinc used.
State the number of moles of hydrogen gas produced.
Calculate the volume, in dm³, of hydrogen gas produced at room temperature and pressure.
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.
Show answer
(i) 0.20 mol
(ii) 0.20 mol
(iii) 4.8 dm³
Common mistakes: Dividing by incorrect Ar; Mixing up molar volume in cm³/dm³
Show mark scheme and worked solution
Marking points
M1 (a(i)) · 1 mark · Calculates number of moles of Zn: 13.0 / 65 = 0.20 (mol)
M2 (a(ii)) · 1 mark · Correctly deduces moles of H2 is same as moles of Zn (1:1 ratio from equation) (follow-through allowed) (follow-through)
A1 (a(iii)) · 1 mark · Calculates volume: 0.20 × 24 = 4.8 (dm³) (follow-through allowed) (follow-through)
Worked solution
(i) Number of moles of Zn = 13.0 / 65 = 0.20 mol
(ii) The equation shows a 1:1 ratio between Zn and H₂, so moles of H₂ = 0.20 mol
(iii) Volume of hydrogen = moles × molar volume = 0.20 × 24 = 4.8 dm³