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Chemistry

When ammonium hydroxide is added to solution B, a pale blue precipitate is formed. This pale blue precipitate dissolves in excess ammonium hydroxide giving an inky blue solution. What is the cation (positive ion) present in solution B? What is the probable colour of solution B.

Ammonia

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Answer

Solution B is Copper Sulphate and cation present is (Cu2+). The colour of solution B is Blue.

Ammonium hydroxide gives a blue precipitate when it combines with a solution of copper salt, due to the formation of Cu(OH)2

CuSO4 + 2NH4OH ⟶ (NH4)2SO4 + Cu(OH)2

The pale blue precipitate of copper hydroxide dissolves in excess of ammonium hydroxide forming tetraamine copper [II] sulphate, an azure blue soluble complex salt.

Cu(OH)2 + (NH4)2SO4 + 2NH4OH ⟶ [Cu(NH3)4]SO4 + 4H2O

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