Question

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?

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

Answer 1

\[\ce{CuSO4 + 2NH4OH -> (NH4)SO4 + \underset{[Pale Blue ppt]}{Cu(OH)2}}\]

The cation present in solution B is Copper (Cu⁺²).

The probable colour of solution B is blue.

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

\[\ce{\underset{(Pale blue ppt)}{Cu(OH)2} + \underset{(Aammonium Hydroxide in excess)}{(NH3)2SO4} + 2NH4OH -> \underset{(Deep blue colouration) or Azure blue sol}{\underset{(Tetraamine copper [II] sulphate)}{[Cu(NH3)4]SO4}} + 4H2O}\]