Displacement reactions involving metal oxides

3 marks · Normal

Zinc oxide can be reduced using carbon:

If you start with 16.2 grams of zinc oxide (ZnO), calculate the maximum mass of zinc metal that can be obtained. (Relative atomic masses: Zn = 65, O = 16, C = 12)

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13.0 g (±0.1)

Also accept: 13 g

Common mistakes: Using incorrect molar masses; Not converting mass to moles

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Marking points

M1 · 1 mark · Calculates moles of ZnO used: mass / Mr (16.2 g / 81).

M2 · 1 mark · States or uses correct 1:1 mole ratio between ZnO and Zn. (follow-through)

A1 · 1 mark · Calculates maximum mass of zinc as 13.0 g. (follow-through)

Worked solution

Mr (ZnO) = 65 (Zn) + 16 (O) = 81

Moles of ZnO = 16.2 g / 81 = 0.200 mol

From the equation, 1 mol ZnO gives 1 mol Zn, so 0.200 mol Zn is made.

Mass of Zn = 0.200 mol × 65 = 13.0 g