Reaction with metals
2 marks · EasyA student reacts 1.2 g of magnesium with excess propanoic acid.
Calculate the maximum volume of hydrogen gas produced at room temperature and pressure. (Molar mass of Mg = 24 g/mol, 1 mol gas = 24 dm³ at r.t.p.)
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1.2 dm³ (±0.05)
Also accept: 1.20 dm³
Common mistakes: Dividing by wrong molar ratio; Wrong volume per mol used
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Marking points
M1 · 1 mark · Calculates moles of Mg: 1.2 / 24 = 0.05 mol. (follow-through)
A1 · 1 mark · Correct final volume of hydrogen: 0.05 × 24 = 1.2 dm³. (follow-through)
Worked solution
Mg + 2CH3CH2COOH → (CH3CH2COO)2Mg + H2
1. Calculate moles of magnesium:
2. 1 mole Mg produces 1 mole H2. Volume of hydrogen = 0.05 mol × 24 dm³/mol = 1.2 dm³.