CHEMISTRY SUBJECT 5071 NOVEMBER 2014 PAPER 02
The performance was quite fair as most students gave fairly good responses showing that the level of understanding of the content is gradually improving. In most cases, the presentation of work was quite accurate and precise with equations well balanced, diagrams well drawn and labelled. In a few cases, the challenge was observed on questions demanding explanations and graphical analysis.
(a) The question was generally well done. A few candidates had problems on identification of the sub-atomic particles – matching them with their correct numbers. Some pupils were referring to the element chlorine – 35 or 37 as the sub-atomic particle.
(b) This was well done by most candidates.
(c) (i) 1. Candidates failed to come up with the correct dot and cross
diagrams specifically on identification of the type of bonding and correct application of the valency of the bonding electrons in the elements.
(ii) 1. most candidates failed to explain the stated physical properties basing on the inter-particle forces (intermolecular forces), or inter-ionic forces.
Most candidates wrongly statetd that the physical state of covalent substances, e.g. CCl4 is determined by intra-molecular bonding instead of the inter-molecular bonding, e.g. the van-der Wall’s forces.
(a) Generally, it was fairy done but a good number of candidates could not identify the type of reaction occurring especially precipitation and hydrolysis.
(b) (i) This proved to be a difficult part for nearly all candidates as they failed
to identify, out of the three elements, the element with the +5, oxidation state.
(ii)&(iii) A good number of candidates came up with the correct equation but failed the calculation part. They could not link correctly the stiochiometric mole ratios between KCIO, and O2. Weak candidates even failed to calculate the Mr value for KCIO3.
(a) Good candidates were able to draw accurately and label the diagram. A number of candidates could not draw the correct diagram of a syringe and in some cases, to identify the correct apparatus for measuring the volume of gas evolved, for example, a syringe, a measuring cylinder or a graduated test tube.
(c) (i)&(ii) candidates could not label the axes correctly ,choosing the most suitable scale to represent. Weak candidates reversed the axes making it difficult to read the volume of the gas produced at 50 minutes.
(iv) Good candidates correctly determined the gradient in order to determine the rate of the reaction.
(v) A good number of candidates failed to describe by way of drawing suitable sketches, the effect of surface areas of contact on rate of reaction. Another challenge emanated for the fact that candidates could not draw the sketches giving the same final volume.
(a) The majority of candidates failed to give the definition of the term saturated. Most of them were dwelling on the fact that saturated means absence of carbon – carbon double bond only.
(b) This part was well done.
(c) & (d) These were fairly done. Most candidates managed to come up with correct isometric alkenes.
The whole question was poorly done with most candidates scoring nothing on this one. Candidates could not come up with the correct organic products showing that they were not familiar with the content, e.g. in (a) the added chlorine atoms did not appear on each of the previously unsaturated carbon atoms instead were appearing on a single carbon atom. On part (b) the formula of the salt showed covalent bonding instead of an ionic bond between the sodium atom and the ethanoate ion. The part (d) the students failed to identify the oxidizing agent, even with the condensation product for part (e).
(a) Most candidates mentioned sulphuric acid as the drying agent instead of anhydrous calcium chloride, totally disregarding the clue given in the question, that of a metal chloride.
(b) The definition for empirical formula in most cases was incomplete wit most candidates defining it as the simplest formula of a compound instead of simplest ration of the constituents atoms in a compound. The part on calculations was generally well done.
(c) It was fairly well done but a good number of candidates gave the wrong observation, i.e. white precipitate instead of white compound.
(a) (i) The general description was well done but weak candidates confused the
structures of the two allotropes.
(ii) This was one of the most difficult parts been for the bright candidates. Most of them simply described the physical properties which were already given in the question instead of explaining the differences in the physical properties of the two allotropies basing on structure and bonding. No comparison was shown in a few correct explanations of the physical properties of the allotropies.
(b) The structure of the silicon polymer was a challenge for most candidates. The other parts were well done.
(a) (ii) The description of fermentation of glucose was not quite el done, most
candidates failed to interpret the question which indicated glucose as the given source and not starch, sucrose or maltose. Weak candidates failed o come yup wit the correct conditions, failing to state the suitable temperature and the presence of the catalyst as well as the anaerobic conditions.
(b) (i) Candidates had a tendency to include aluminum oxide as a reactant in
the equation when it was only acting as a dehydrating agent.
(ii) The test for the alkene (ethane) was generally well done.
(iii) The question was fairly done but average and below average students could not draw the correct and well labelled diagram for the production of ethane. Some candidates could not display knowledge of the fact that ethanol cannot be heated directly as it is inflammable.
C:\CHIEF EXAMINERS’ REPORTS\CER - 5071-02 - NOVEMBER 2014