Chemistry
State your observations when ammonium hydroxide solution is added drop by drop and then in excess to each of the following:
(i) copper sulphate solution
(ii) zinc sulphate solution.
Ammonium Hydroxide
ICSE 2016
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Answer
(i) Pale blue precipitate of Cu(OH)2 is formed, which becomes deep blue when excess of ammonium hydroxide is added.
CuSO4 + 2NH4OH ⟶ (NH4)2SO4 + Cu(OH)2 ↓
Cu(OH)2 + (NH4)2SO4 + 2NH4OH [in excess] ⟶ 4H2O + [Cu(NH3)4]SO4
(ii) Gelatinous white precipitate of zinc hydroxide is formed which becomes colourless solution on adding excess of ammonium hydroxide.
ZnSO4 + 2NH4OH ⟶ (NH4)2SO4 + Zn(OH)2 ↓
Zn(OH)2 +(NH4)2SO4 + 2NH4OH [in excess] ⟶ 4H2O + [Zn(NH3)4]SO4
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