This question was attempted by majority of the candidates however, the performance was fair.
In question (a)(i)-(iii), most candidates could not correctly state two observations and corresponding conclusions drawn from the J.J. Thomson’s Cathode ray experiment They were also unable to name the particle generated in the cathode ray experiment and mention two other fundamental particles in an atom.
The expected response from candidates were
(i) - cathode rays are deflected by electric/magnetic fields therefore,
they carry charges.
- they are deflected by negative electric palate/attracted by the positive plate therefore, they are negatively charged.
- they are produced by all matter therefore, they are present in all matter.
(ii) Electrons
(iii) Protons and neutrons.
In question b(i), majority of the candidates were able to indicate the nature of
bond present in W, X, and Y as ionic, metallic and covalent respectively.
In question (b)(ii), many candidates did not know that W does not conduct electricity in the solid state because the ions are not mobile; X conducts electricity in the solid state because there are free electrons/delocalized electrons which flow through and carry current and Y cannot be a pure substance because it does not have fixed melting point or melting point range is wide.
In question (b)(iii), only a few candidates were able to outline the separation of mixture of W and Y thus:
- add water and stir to dissolve W
- filter to obtain Y as residue and W as filtrate
- heat/evaporate/concentrate filtrate
- crystallize
- filter/decant to obtain W
In question (c) (i), most candidates explained that graphte is used as lubricant because the carbon atoms in it are arranged in layers and the weak forces of attraction between these layers of carbon allow the layers to slide over one another.
In question (c) (ii), majority of the candidates did not know that potassium hydrogen trioxocarbonate (IV) removes acid/HCl fumes but a good number of them correctly stated that fused calcium chloride is used as drying agent.
