3.1.4 Qualitative Analysis
Questi
on Acceptable Answer Mark Additional Guidance
1 a) lime water
b) Limewater turns milky/cloudy
1 Accept aqueous calcium
hydroxide
2 a) white ppt forms
b) we cannot be sure if solution A
contained sulphate ions or not
because sulphate ions from sulphuric
acid are in the solution and the result in
white ppt formation
1
1
1
3 a) Sodiumcarbonate
4 a) pungent smelling irritating gas is
evolved.
b) white ppt
c) ppt dissolves to give colourless
solution
1
1
1
Allow half credit if only
ammonia is evolved
mentioned
5 The sequence of tests required is
carbonate, sulfate then halide.
This will prevent false results of as both
BaCO3 and Ag2 SO4 are insoluble.
2
1
6 It is either bromide ion or iodide ion
Treat with conc ammonia
Silver bromide dissolves in concentrated
ammonia
Silver iodide does not react with
ammonia – it is too insoluble.
0.5
0.5
1
1
Donot allow if
‘concentrated’ not
mentioned
7 The test solution is made acidic with
nitric acid,
and then Silver nitrate solution is added
dropwise.
Bromides produce a cream precipitate
Treat with conc ammonia to be sure..
silver bromide dissolves in conc ammonia
1
1
1
1
8
Io
n
Ppt
colo
ur
whe
n
silve
r
nitra
te
adde
d
Observa
tion
when
ppt
treated
with
dilute
ammoni
a
Observatio
n when
ppt
treated
with dilute
ammonia
6 1 mark each of correct
colour
0.5 for each correct
observation in dilute
and conc ammonia
1
