O-LevelChemistryElectrolysis5070/21 · May/June 2016 · Q710 Marks

Silver nitrate has the formula AgNO3.

(a)Describe how a pure sample of silver nitrate crystals can be prepared from solid silver oxide, which is insoluble in water.[4]
(b)(i)Aqueous zinc chloride is added to a sample of acidified aqueous silver nitrate. Describe what you would observe.[1]
(b)(ii)Construct the ionic equation, with state symbols, for the reaction that occurs.[2]
(c)(i)Aqueous silver nitrate is electrolysed using graphite electrodes. Identify the product formed at the cathode (negative electrode).[1]
(c)(ii)Oxygen and water are formed at the anode (positive electrode). Construct the equation for the reaction at the anode.[1]
(d)Silver nitrate decomposes on heating to form Ag2O, NO2 and O2. Construct the equation for this reaction.[1]

Mark scheme

Marking points from the official mark scheme (May/June 2016). The mark or mark type is shown in brackets.

[4] 1 mark each of any four from: • Use of excess silver oxide • Use of nitric acid • Warm the solution / use warm nitric acid / use hot nitric acid • Filter mixture to get the solution • Evaporate some of the solution and leave / leave to crystallise / warm to crystallisation point / leave on window sill (to crystallise) / evaporate solution then cool
[1] White precipitate (1)
[2] Ag⁺(aq) + Cl⁻(aq) → AgCl(s) Correct formulae (1) Correct state symbols dependent on the correct formulae (1)
[1] Silver (1)
[1] 4OH⁻ → O2 + 2H2O + 4e⁻ (1)
[1] 4AgNO3 → 2Ag2O + 4NO2 + O2 (1)

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