NumericalModerate1 mark
1(f)
Calculate:
The volume occupied by 80 g of carbon dioxide at STP.
Topic: Mole concept, gas volumes and stoichiometry
Previous-year question practice database
Answer
Exam answer
Given: mass of CO₂ = 80 g.
Molar mass of CO₂ = 12 + (2 × 16) = 44 g mol⁻¹
Moles = 80 ÷ 44 = 1.818 mol
Volume at STP = moles × 22.4 = 1.818 × 22.4 = 40.7 litres
Volume occupied ≈ 40.7 litres at STP
Explanation
Mass to moles, then moles to volume — the two conversions never merge into one. Multiplying 80 by 22.4 straight away gives 1792 litres, which is absurd.
Sanity check the size: 80 g is a bit under two moles, so the volume must be a bit under 2 × 22.4 = 44.8 litres. 40.7 fits.
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