CHEMISTRY PRACTICAL
CLASS – VIII
Experiment # 06 – “Testing for cobalt (II) ion and ammonium ion using alkaline precipitation”.
List of apparatus and chemicals:
cobalt (II) chloride salt and ammonium chloride salt
distilled water
test tubes
sodium hydroxide solution and ammonium hydroxide solution
red litmus paper
Method:
Solutions of cobalt (II) chloride are made in two separate test tubes using distilled water.
In one test tube few drops of sodium hydroxide is added and in another test tube few drops of
ammonium hydroxide is added.
The precipitate, if formed, is observed and recorded.
Most of the precipitate formed is then thrown out from the test tubes.
Excess sodium hydroxide and ammonium hydroxide solutions are then added to the precipitate in
respective test tubes.
The solubility of the precipitate in excess hydroxide solutions is observed and recorded.
Solution of ammonium chloride is made in a test tubes using distilled water.
Few drops of sodium hydroxide are added to the salt solution.
The precipitate, if formed, is observed and recorded.
The test tube is gently heated with a moist red litmus paper placed on the mouth of the test tube.
Result of observation:
cation
few drops of
sodium
hydroxide
excess
sodium
hydroxide
few drops of
ammonium
hydroxide
excess
ammonium
hydroxide
cobalt (II)
Co2+
blue-violet
precipitate
formed
precipitate
remains
insoluble
blue-green
precipitate
formed
precipitate
remains
insoluble
ammonium
NH4+
no precipitate
formed;
upon heating, a
colourless
pungent gas is
produced that
turns moist red
litmus paper
blue.
[The colourless
gas produced is
ammonia]