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]