Calculations involving gas volumes
3 marks · NormalPropane burns in oxygen according to the equation:
Calculate the total volume, in dm³, of carbon dioxide gas formed at rtp when 4.4 g of propane reacts completely. (M_r(C_3H_8) = 44)
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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7.2 dm³ (±0.1)
Must show: calculating moles of propane, relating moles of propane to CO₂, using molar volume
Also accept: 7.20 dm³
Common mistakes: not multiplying by 3 for 3 mol CO₂; wrong molar volume
Show mark scheme and worked solution
Marking points
M1 · 1 mark · Calculates moles of propane: 4.4 / 44 = 0.10 mol
M2 · 1 mark · Relates moles of CO₂ formed: 0.10 × 3 = 0.30 mol CO₂ (follow-through)
A1 · 1 mark · Calculates total volume: 0.30 × 24 = 7.2 dm³ (unit needed) (follow-through)
Worked solution
Moles of propane = 4.4 g / 44 = 0.10 mol
From the equation: 1 mole C₃H₈ gives 3 moles CO₂, so 0.10 mol → 0.30 mol CO₂
Volume = moles × molar volume = 0.30 × 24 = 7.2 dm³