Lesson: Chapter 16 — Changes of Matter

16.4. Extracting metals 3 of 8 Reset answers

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Question 3

By Fe₂O₃ + 3CO → 2Fe + 3CO₂, what mass of iron is produced when 100 kg of haematite is reduced? (Fe = 56, O = 16)

A 160 kg B 112 kg C 56 kg D 70 kg

The right answer is the one marked above.

70 kg. Fe₂O₃ = 160 g mol⁻¹ and 2Fe = 112 g. So 100 × (112 ÷ 160) = 70 kg.

112 kg comes from forgetting to divide by 160 g — that is the figure for one mole, not for 100 kg. The ratio must always be applied.

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