Iron ores, extraction, steel and alloys
Answers are for parents and teachers.
1
A 4-tonne sample of ore contains 75 % Fe₂O₃. How many tonnes of iron does it hold? (Fe₂O₃ is 70 % iron.)
Fe₂O₃: 4 × 0.75 = 3.0 tonnes. Iron: 3.0 × 0.70 = 2.1 tonnes.
2
Roasting on paper: FeCO₃ → FeO + CO₂ and then 4FeO + O₂ → 2Fe₂O₃. Starting from 232 g of FeCO₃ (Fe = 56, C = 12, O = 16) find the mass of FeO and the final mass of Fe₂O₃ and of oxygen used.
n(FeCO₃) = 232 ÷ 116 = 2 mol, so n(FeO) = 2 mol = 144 g. Then 2 mol FeO + 0.5 mol O₂ → 1 mol Fe₂O₃ = 160 g, using 0.5 × 32 = 16 g of O₂ (144 + 16 = 160).
3
Fe₂O₃ + 3CO → 2Fe + 3CO₂. For 48 g of Fe₂O₃ find the mass of CO needed and of iron formed (Fe = 56, C = 12, O = 16).
n = 48 ÷ 160 = 0.3 mol. CO: 0.9 mol × 28 = 25.2 g. Fe: 0.6 mol × 56 = 33.6 g.
4
Name the type of each alloy: (a) steel with 0.5 % carbon, (b) chromium in iron, (c) the compound Fe₃C, (d) nickel with copper.
(a) interstitial, (b) substitutional, (c) intermetallic compound, (d) substitutional (nearly equal atom sizes).
5
A pupil says: “Steel is a compound of iron and carbon.” Correct this in two sentences.
Steel is an alloy, a mixture of iron with a small amount of carbon, and the amount can vary. The carbon atoms sit in the gaps of the iron lattice. Fe₃C, by contrast, is a true compound with a fixed formula.