Iron and its oxides
Answers are for parents and teachers.
1
Fe + H₂SO₄ → FeSO₄ + H₂. For 22.4 g of iron (Fe = 56, S = 32, O = 16) find the volume of hydrogen at STP (22.4 L/mol) and the mass of FeSO₄ (M = 152 g/mol).
n(Fe) = 0.4 mol. H₂: 0.4 × 22.4 = 8.96 L. FeSO₄: 0.4 × 152 = 60.8 g.
2
Fe₂O₃ + 3H₂SO₄ → Fe₂(SO₄)₃ + 3H₂O. For 32 g of Fe₂O₃ (H = 1, S = 32, O = 16) find the mass of acid needed and of Fe₂(SO₄)₃ formed (M = 400 g/mol).
n(Fe₂O₃) = 0.2 mol. Acid: 0.6 mol × 98 = 58.8 g. Salt: 0.2 × 400 = 80 g.
3
2Fe(OH)₃ → Fe₂O₃ + 3H₂O. What mass of Fe(OH)₃ (M = 107 g/mol) must be heated on paper to give 8.0 g of Fe₂O₃ (M = 160 g/mol)?
n(Fe₂O₃) = 8.0 ÷ 160 = 0.05 mol, so n(Fe(OH)₃) = 0.1 mol × 107 = 10.7 g.
4
Fe₃O₄ + CO → 3FeO + CO₂. For 11.6 g of Fe₃O₄ (C = 12, O = 16) find the mass of FeO formed, of CO needed and of CO₂ formed.
n(Fe₃O₄) = 0.05 mol. FeO: 0.15 mol × 72 = 10.8 g. CO: 0.05 × 28 = 1.4 g. CO₂: 0.05 × 44 = 2.2 g. Check: 11.6 + 1.4 = 13.0 = 10.8 + 2.2.
5
A pupil says: “Fe₃O₄ is iron(II) oxide because it is black, like FeO.” Correct this in two sentences.
Colour does not decide the formula. Fe₃O₄ is a mixed oxide, FeO·Fe₂O₃, with iron in both the +2 and +3 states, and it is strongly magnetic, while FeO is not.