Adding distilled water to the specimen in a boiling tube and making accurate observations were successfully done by most candidates.
Few candidates however were not able to give logical deductions from their observation while some could neither carry out the tests as prescribed nor were able to record their observations.
It was observed that many candidates still confused residue with precipitate and or solid. Other mistakes include: white ppt after filteration instead of white residue; clear filtrate instead of colourless filtrates; ppt disappears instead of ppt dissolves; white chalky ppt instead of white gelationous ppt and carrying out the test on the dry sample instead of solution as demanded by the question.
TEST |
OBSERVATION |
INFERENCE |
a) C + water, mixture stirred
and filtered |
Partly dissoves/soluble Colourless filtrate
White residue (do not accept ppt/solid) |
C contains soluble and insoluble salts |
b) Filtrate + Pb (NO3)2(aq)
Boiled
then cooled |
White precipitate formed
Precipitate dissovles
Precipitate reappeares |
Cl-, SO42- or CO32-any for (2 marks) (SO32- do not score but do not penalize)
Cl- present
Cl- confirmed |
c) (i) Residue + dil HNO3 |
Effervescence/bubles/gas evolved colourless odourless gas. Gas turns lime water milky. |
CO2 evolved from CO32- |
(ii) Solution from (c)(i) +
NaOH(aq) in drops then in
excess |
White gelatinous ppt formed
Precipitate dissovles |
Zn2+ or A13+
Zn2+ or A13+ |
(iii) Solution from (c)(i) +
HN3(aq)
in drops
then in excess |
White gelatinous
Precipatate form
Precipitate dissovles |
Zn2+ or A13+
Zn2+ confirmed |