O-LevelChemistryChemistry of the Environment5070/21 · May/June 2021 · Q59 Marks

Iron pyrite, FeS2, is an ore of iron. When heated in air, FeS2 produces both iron(III) oxide and sulfur dioxide.

(a)Balance the equation shown. FeS2 + _____ O2 → _____ Fe2O3 + _____ SO2[1]
(b)Describe one environmental problem caused by sulfur dioxide in the air.[1]
(c)Describe how sulfur dioxide is converted into sulfuric acid in the contact process.[3]
(d)State one other use of sulfur dioxide.[1]
(e)Iron(III) oxide, coke, limestone and hot air are heated together in a blast furnace to make molten iron. Describe the function in the blast furnace of:
(e)(i)coke[1]
(e)(ii)limestone[1]
(e)(iii)hot air.[1]

Mark scheme

Marking points from the official mark scheme (May/June 2021). The mark or mark type is shown in brackets.

5(a) 4FeS2 + 11O2 → 2Fe2O3 + 8SO2
5(b) acid rain / erodes buildings / corrodes buildings
5(c) sulfur dioxide reacted with oxygen to make sulfur trioxide (1)
5(c) this reaction uses a V2O5 catalyst / temperatures between 450 and 600 °C / 1 to 10 atmosphere pressure (1)
5(c) sulfur trioxide reacted with H2SO4(l) to make oleum which is then reacted with water (to make sulfuric acid) (1)
5(d) bleaching (wood pulp) / preservative
5(e)(i) reacts with oxygen to provide energy for the reaction / makes carbon monoxide / reduces carbon dioxide
5(e)(ii) (decomposes) to make calcium oxide (which removes impurities)
5(e)(iii) provides oxygen for the coke to burn / makes carbon dioxide from (coke)

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