Question

What happens when ammonia solution is added first dropwise and then in excess to the following solution:

CuSO₄

Write a balanced equation for this reaction.

Give the reactions to explain what happens when ammonia solution is added drop by drop till it is in excess to the following solution:

CuSO₄

Answer 1

Adding ammonium hydroxide drop by drop to copper sulphate solution forms a pale blue precipitate of copper hydroxide.

\[\ce{\underset{\text{blue}}{CuSO4} + 2NH4OH -> \underset{\text{pale blue ppt.}}{Cu(OH)2\downarrow} + \underset{\text{colourless in solution}}{(NH4)2SO4}}\]

Adding excess ammonium hydroxide dissolves the precipitate to form a deep blue complex solution.

\[\ce{Cu(OH)2 + 4NH4OH -> \underset{(Deep Blue Solution)}{\underset{Tetrammine copper (II) hydroxide}{[Cu(NH3)4](OH)2}} + 4H2O}\]