O-LevelChemistryStoichiometry5070/22 · May/June 2017 · Q710 Marks

Copper reacts with hot concentrated aqueous sulfuric acid. Cu(s) + 2H₂SO₄(aq) → CuSO₄(aq) + SO₂(g) + 2H₂O(l)

(a)Suggest what you would observe when copper reacts with hot concentrated aqueous sulfuric acid.[1]
(b)(i)Name the salt of formula CuSO₄.[1]
(b)(ii)Copper is oxidised when it reacts with concentrated sulfuric acid. Use the equation to explain that copper has been oxidised.[1]
(c)An excess of copper is added to 25.0 cm³ of hot 14.0 mol/dm³ H₂SO₄ Use this information, together with the equation, to calculate the maximum volume of SO₂ formed. The gas volume is measured at room temperature and pressure.[3]
(d)(i)To a small sample of CuSO₄(aq), a student adds aqueous sodium hydroxide drop by drop until it is in excess. Describe what would be observed.[1]
(d)(ii)The student repeats the experiment but adds aqueous ammonia instead of aqueous sodium hydroxide. Describe what would be observed.[2]
(e)Copper(I) chloride, CuCl, decomposes to form CuCl₂ and Cu. Construct the equation for this reaction.[1]

Mark scheme

Marking points from the official mark scheme (May/June 2017). The mark or mark type is shown in brackets.

B7(a) Blue solution / bubbles
B7(b)(i) Copper(II) sulfate
B7(b)(ii) Copper loses electron(s)
B7(c) Moles of acid = 0.025 × 14.0 OR 0.35 (1) Moles of sulfur dioxide = 0.175 (1) Volume of gas = 4.2 dm³ / 4 200 cm³ (1)
B7(d)(i) Blue precipitate / blue solid (which does not redissolve)
B7(d)(ii) Blue precipitate / blue solid (1) In excess ammonia gives a dark blue solution (1)
B7(e) 2CuCl → CuCl₂ + Cu

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