The question was attempted by most candidates and the performance was fair .
Candidates copied and completed the table however, a good number of them lost marks
because of wrong observations and inferences and inability to state the composition of salt
C. The correct table from candidates was as follows:
|
Test |
Observation |
Inference |
(a) (i) |
C + l0cm3 distilled water, |
C partially dissolved to give |
C contains soluble |
|
and filtered after stirring |
colourless filtrate and white |
and insoluble |
|
|
residue |
Compounds/salts |
(ii) |
Filtrate + litmus paper |
No visible reaction/Litmus |
Neutral filtrate |
|
|
paper remains unchanged |
|
(b) (i) |
First portions of filtrate + |
White ppt |
|
|
AgN03(aq) then + HN03(aq) |
Ppt undissolved/remained |
|
|
+ NH3(aq) |
Ppt insoluble |
|
|
|
Ppt dissolved |
CI- confirmed |
(ii) |
Second portion of filtrate + |
|
|
|
NaOH(aq) in drops |
White gelatinous precipitate |
Zn2+ or A}3+ |
|
Then in excess |
Precipitate |
Zn2+ or A}3+ |
|
|
soluble/ dissolved |
|
(iii) |
Third portion of filtrate + |
White gelatinous |
Zn2+ or A}3+ |
|
NH3(aq) in drops |
Precipitate |
Zn2+ confirmed |
|
Then in excess |
Precipitate dissolved |
|
(c) (i) . |
Portion of residue + iodine |
Blue-black colouration |
|
|
solution |
|
Starch present |
(ii) |
Portion of residue + |
No blue - black colouration |
Strach hydrolysed |
|
HCI(aq) and boil, cool and |
or brown colour of iodine |
|
|
add iodine solution |
remains |
|
C contains Zinc chloride/ZnCl2 and starch.
