The question was attempted by most candidates and the performance was poor.
In part (a), candidates were unable to outline how a mixture of ammonium chloride,
potassium chloride and lead (II) chloride could be separated in the laboratory. The
expected answers from candidates were as follows:
- Pour the mixture into an evaporating dish and cover with a glass funnel.
- Heat the mixture
- Ammonium chloride sublimes and collects in the funnel
- Add distilled water to the mixture
- Potassium chloride dissolves
- Filter and collect the lead (II) chloride as residue
- Evaporate the filtrate to dryness to obtain potassium chloride.
In part (b), candidates correctly named calcium chloride/calcium oxide/Silica gel as
solid drying agent in (i) and concentrated tetraoxosulphate (VI) acid as liquid drying
agent in (II).
In part (c), candidates correctly mention one laboratory apparatus used in(i)-(v) as follows:
(i) Volumentric/standard flask
(ii) Liebig condenser
(iv) kipps apparatus
(v) pH meter.
In part (d) (i), candidates could not describe a chemical test to distinguish between pure
water and sodium tetraoxosulphate (VI) solution. The required description from
candidates was as follows:
- To a sample of each liquid, add BaCl2(aq)
- The sample that forms white precipitate is sodium tetraoxosulphate(V1)
- No precipitate shows the presence of pure water.
In(d) (ii), only few candidates stated NaOH(aq)/NH3(aq) as the reagent suitable to distinguish
the two white substances.