O-LevelChemistryMetals & Reactivity5070/22 · May/June 2020 · Q810 Marks

Copper is a transition element.

(a)State two properties that are typical of the compounds of a transition element. 1 .......................................................................................................... 2 .......................................................................................................... [2][2]
(b)Aqueous copper(II) sulfate reacts with aqueous potassium iodide. The ionic equation for this reaction is shown. 2Cu2+(aq) + 4I¯(aq) → 2CuI(s) + I2(aq) Explain how this equation shows that the reaction involves oxidation.[1]
(c)Anhydrous copper(II) sulfate decomposes when heated strongly. CuSO4(s) → CuO(s) + SO3(g) A sample of 6.40 g of CuSO4 is heated until all of the sample has thermally decomposed. Calculate the volume of sulfur trioxide formed, in dm³, measured at room temperature and pressure. volume of sulfur trioxide ............................................................ dm³ [3][3]
(d)(i)Iron reacts with aqueous copper(II) sulfate to make aqueous iron(II) sulfate and copper. Construct the ionic equation for this reaction.[1]
(d)(ii)Suggest one observation that would be seen during this reaction.[1]
(e)Describe a chemical test that can be used to distinguish between aqueous solutions of iron(II) sulfate and copper(II) sulfate. chemical test ................................................................................................................................................................................. result with iron(II) sulfate ............................................................................................................................................................. result with copper(II) sulfate .......................................................................................................................................................... [2][2]

Mark scheme

Marking points from the official mark scheme (May/June 2020). The mark or mark type is shown in brackets.

[1] 8(a) catalysts (1)
[1] 8(a) coloured (1)
[1] 8(a) show variable oxidation number (of the transition element) (1)
[1] 8(b) iodide (ion) loses electrons / I¯ loses electrons (1)
[1] 8(c) Mr of CuSO4 = 160 (1)
[1] 8(c) moles of CuSO4 or moles of SO3 = 0.04 (1)
[1] 8(c) volume of SO3 (= 24 × 0.04) = 0.96 (dm³) (1)
[1] 8(d)(i) Fe + Cu2+ → Fe2+ + Cu (1)
[1] 8(d)(ii) solution changes from blue to green / pink solid formed / pink coating / pink deposit
[1] 8(e) (aqueous) ammonia (1)
[1] 8(e) iron(II) sulfate – green ppt AND copper(II) sulfate blue ppt that redissolves in excess to give dark blue solution with NH3 (1)
[1] 8(e) OR (aqueous) sodium hydroxide (1)
[1] 8(e) iron(II) sulfate – green ppt AND copper(II) sulfate blue ppt (1)