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 Chemistry Paper 1 (Practical) ,May/June 2008
 Questions: 1 2 3 4 5 6 Main
Weakness/Remedies
Strength

Question 5

(a) Sample F is a solution extracted from a fruit.
Test F with litmus papers. [3 marks]

(b )Divide F into three portions in test tubes.

(i) To the first portion add 2 drops of methyl orange.
(ii) To the second portion add half a spatula of Na2CO3.
(iii) To the third portion add few pieces of magnesium ribbon.   [9 marks]

(c) Put about 1 cm3 of bench  H2SO4 into three separate test tubes.
(i) To the first portion in the test tube add 2 drops of methyl orange.
(ii) To the second portion in the test tube add half a spatula of Na2CO3.
(iii) To the third portion in the test tube add few pieces of magnesium  ribbon.  [7 marks]
(d) Compare the reactions of sample F in 2(b) with that of dilute H2SO4 in 2(c)  [1 mark]

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OBSERVATION

The question was well attempted by candidates.

In (a), candidates correctly tested sample F with both red and blue litmus paper with correct observations and inference as follows:

 Test Observation Inference F + litmus Turns blue litmus paper red but had no effect on red litmus paper F is acidic

In (b)(i), some of the candidates showed poor knowledge of the colour change of methyl orange in acidic solution.  However, majority of the candidates correctly carried out the required test and made correct observations and inferences in b(ii)-(iii) as follows:

 Test Observation Inference (b)(i)                    (ii)                   (iii) F + methyl orange              F + Na2CO3       F + Mg ribbon Turns methyl orange red/pink    Effervescence/ evolution/bubbles of a colourless gas that turned lime water milky/turn blue litmus paper red. Effervescence/evolution of colourless gas which gives pop sound with burning splint F is acidic CO2  liberated from Na2CO3.   F is an acid. H2 liberated

In (c)(i), some of the candidates could not deduce correctly the colour change of methyl orange in acidic solution.  However, a good number of them correctly carried out the required test and made correct observations with logical inferences in c(ii)-(iii) as tabulated below.

 Test Observation Inference (c)(i)                               (ii)   (iii) H2SO4(aq)+ methyl  orange          H2SO4(aq)     + Na2CO3   H2SO4(aq) + Mg ribbon Methyl orange turned red           Effervescence/ evolution/bubbles of a colourless gas that turned lime water milky/turn blue litmus paper red. Effervescence/evolution of colourless gas which gives pop sound with burning splint CO2  liberated.   Gas is H2
In (d), candidates correctly deduced that the reaction of sample F is similar to that of dilute H2SO4 but majority of them did not mention that it is more vigorous in H2SO4 than F hence, lost some marks.