O-LevelChemistryElectrolysis5070/21 · Oct/Nov 2018 · Q210 Marks

Zinc reacts with aqueous nickel(II) nitrate. Zn(s) + Ni(NO3)2(aq) → Zn(NO3)2(aq) + Ni(s)

(a)(i)By referring to the equation, explain why this is a redox reaction.[2]
(a)(ii)Construct the ionic equation for this reaction.[1]
(b)Draw a labelled diagram to show how a fork made of nickel is electroplated with silver.[3]
(c)Aqueous ammonia is added, with mixing, to a solution containing zinc ions until no further change occurs. What observations would be made during this test?[2]
(d)Blocks of zinc are attached to the underside of ships made of iron to stop them from rusting. Explain how zinc stops the ships from rusting.[2]

Mark scheme

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

[2] zinc loses electrons which is oxidation (1) nickel ions gain electrons which is reduction (1)
[1] Zn + Ni²⁺ → Zn²⁺ + Ni
[3] workable arrangement with two electrodes dipping in liquid connected to power supply with two wires and no obvious gaps in the wiring (1) nickel or the fork is negative electrode and silver is positive electrode (1) electrolyte is labelled silver ions OR soluble silver salt OR electrolyte (1)
[2] (at first) white precipitate (1) dissolves (in excess ammonia) / soluble in excess (ammonia) / colourless solution (in excess ammonia) (1)
[2] zinc is more reactive than iron (1) zinc corrodes instead of iron / zinc oxidises instead of iron (1)

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