Majority of the candidates attempted this question, but the performance was poor on the average.
In part (a), some candidates gave the chemical formulae instead of name thereby loosing marks.
In part (b), most of the candidates could not correctly distinguished between HCl and CH3COOH chemically.
In (c) majority of the candidates did poorly. the question required knowledge of hydrolysis of simple salts. Candidates rather used litmus test and lost valuable marks.
In (d) (i) some candidates reported the colour of AgCl when exposed as black instead of grey.
In d(ii) majority of the candidates that attempted the question answer it theoretically. Some gave the required result but mentioned sulphur as being deposited instead of just mentioning a yellow deposit.
The expected answers include:
3.
(a)(i) Calcium oxide
(ii) (Dry) hydrogen gas/methane/butane
(iii) Anhydrous copper (II) tetraoxosulphate (VI) / Anhydrous cobalt (II) chloride
(b) Pour silver trioxonitrate (V) solution/Lead (II) trioxonitrate (V) solution
into each of the solutions.
White precipitate is formed with HCl, no visible reaction
with ethanoic acid.
OR
To each sample of the solution add ethanol followed by few drops of tetraoxosulphate (VI) acid and heat.
No sweet smell with HCl.
Sweet smell with ethanoic acid
(c) Na2CO3 is a salt of a weak acid and a strong base.
It undergoes hydrolysis to give alkaline solution.
Al2(SO4)3 is salt of a strong acid and weak base.
It undergoes hydrolysis to give acidic solution.
(d) (i) White colour of AgCl turns grey
(ii) Purple colour of acidified potassium
tetraoxomanganate (VII) solution turns colourless
with yellow deposit/precipitate/solid.
