CHEMISTRY SUBJECT 5071 NOVEMBER 2014 PAPER 04
Candidates performed well in questions 2, 3 and 4 and had challenges with question 1. There is an improvement in candidates’ ways of tackling the alternative to practical paper. Teachers are encouraged to emphasise on syllabus specifications to candidates especially on accuracy in taking readings from instruments and rounding off of numerical answers.
They should also encourage candidates to write their answers only in the spaces provided and write neatly.
Candidates should also show all the necessary working on the question paper. Rough work should not be done on the question paper.
COMMENTS ON INDIVIDUAL QUESTIONS
(a) Most candidates were able to read and record the volumes from the burette correctly to at least one decimal place. Subtractions were done correctly.
Some candidates, however, had problems with the summary. They could not identify the best titrations. Instead of ticking two titrations which are within 0.2cm3, some ticked three titrations or one titration.
Teachers should emphasize on ticking the best results instead of just giving the average titre as candidates may lose marks if they make mistakes in the calculation for average titre.
(b) (i) & (ii) These parts were fairly done, although a few candidates took organic
acids as a homologous series.
(iii) Most candidates could not write the equation correctly. Formula for products was a challenge to most, which made it difficult to balance the equation though they knew they should balance. Candidates failed to realize that the acid is tri-basic, as they used only one –COOH group. Use of the displayed formula assisted candidates in getting the correct balanced equation.
(c) (i). 1. Most candidates were able to calculate the number of moles of sodium
hydroxide using the correct formula.
A few candidates, however, lost marks of the use of M to represent the number of moles in the formula, i.e. they stated the formula as M = CV instead of n – cv.
Some gave the formula wrongly as .
(i). 2. Candidates could not relate the question to 1(b)(iii), i.e. the equation. They did not use stiochiometric rations to calculate the number of moles of citric acid. Instead, they used .
(ii) Though candidates knew how to calculate the mass of citric acid, the failed to calculate the relative molecular mass of citric acid though the formula was given.
This question was poorly done. Most candidates did not calculate the mass of citric acid in 100 cm3 of the drink. They used mass of citric acid in the average titre to calculate the percentage composition, i.e.:
(a) Candidates were able to give correct observations though a few gave vague answers like a gas is produced instead of saying gas bubble/effervescence.
(b) Fairly done.
(c) Fairly done.
(d) Most candidates got the test correctly but failed to state that NAOH was supposed to be added in excess since observations were made with excess solution. Marks were also lost on the test for ammonia. Candidates were simply writing that gas turns red litmus paper blue instead of saying gas turns damp red litmus paper blue.
Teachers should emphasize damp litmus paper so that candidates do not lose marks unnecessarily.
(e) Fairy done, though a few candidates thought Pb2+ (aq) was used to test got halides instead of confirming the sulphate ions.
NB: Teachers should emphasize on linking tests, observations and deductions. Candidates lost marks for not linking observations to tests.
(f) Fairy done.
This question was fairly done. Candidates were able to read the volumes and record in the table.
Calculations were done correctly.
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