Displacement reactions involving metal oxides
3 marks · NormalIron(III) oxide can be reduced by aluminium in a displacement reaction:
Calculate the maximum mass of iron produced if 8.0 g of iron(III) oxide is reduced completely using this reaction. (Relative atomic masses: Fe = 56, Al = 27, O = 16)
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5.6 g of iron g (±0.1)
Common mistakes: Using incorrect molar mass; Not multiplying by 2 for number of Fe atoms produced
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Marking points
M1 · 1 mark · Calculates the number of moles of Fe2O3 correctly.
M2 · 1 mark · Works out the correct amount (in moles) of Fe produced from the reaction equation. (follow-through)
A1 · 1 mark · Converts moles to grams for Fe using 56 g/mol and gives the final answer. (follow-through)
Worked solution
Relative formula mass of Fe2O3 = (2 × 56) + (3 × 16) = 112 + 48 = 160
Moles of Fe2O3 = 8.0 g / 160 = 0.05 mol
From the equation: 1 mol Fe2O3 gives 2 mol Fe. So, 0.05 mol Fe2O3 gives 0.10 mol Fe.
Mass of Fe = 0.10 mol × 56 g/mol = 5.6 g