O-LevelChemistryMetals & Reactivity5070/21 · May/June 2018 · Q610 Marks

Copper pyrites is an ore containing compounds of copper. One of the compounds in the ore is CuFeS2.

(a)Calculate the mass of copper in 20.0 tonnes of CuFeS2. mass of copper ..................................................... tonnes[2]
(b)CuFeS2 is heated in air. Copper(II) oxide, iron(III) oxide and sulfur dioxide are formed. Construct the equation for this reaction.[2]
(c)Copper(II) oxide can be reduced by heating with carbon to form copper. Construct the equation for this reaction.[1]
(d)(i)Copper made by this reduction is impure. Impure copper can be purified using electrolysis. Name the electrolyte used.[1]
(d)(ii)What are the electrodes made from? positive electrode (anode) negative electrode (cathode)[2]
(d)(iii)Write the equations for the reactions at both electrodes. positive electrode (anode) negative electrode (cathode)[2]

Mark scheme

Marking points from the official mark scheme (May/June 2018). The mark or mark type is shown in brackets.

[2] 6(a) M_r = 184 (1) (% copper = 34.8 so mass of copper = % × 20) = 6.96 (1)
[2] 6(b) 2CuFeS2 + 6½O2 → 2CuO + Fe2O3 + 4SO2 correct formulae (1) balancing - dependent on correct formulae (1)
[1] 6(c) 2CuO + C → 2Cu + CO2 OR CuO + C → Cu + CO (1)
[1] 6(d)(i) (aqueous) copper(II) sulfate (1)
[2] 6(d)(ii) anode - impure copper (1) cathode - (pure) copper (1)
[2] 6(d)(iii) anode: Cu → Cu²⁺ + 2e⁻ (1) cathode: Cu²⁺ + 2e⁻ → Cu (1)

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