Question

State what you will observe when ammonium hydroxide solution is added to copper sulphate in excess.

Answer 1

Reaction with copper(II) sulphate$\left({\mathrm{CuSO}}_4\right)$:

• Ammonium hydroxide $\left({\mathrm{NH}}_4\mathrm{OH}\right)$ reacts with copper(II) sulphate solution to form a pale blue colored precipitate of $\mathrm{Cu}{\left(\mathrm{OH}\right)}_2$ which dissolves in excess of ammonium hydroxide to form a deep blue colour soluble complex salt.
• ${\mathrm{CuSO}}_4\left(\mathrm{s}\right)+2{\mathrm{NH}}_4\mathrm{OH}\left(\mathrm{l}\right)⟶\mathrm{Cu}(\mathrm{OH}{)}_2\left(\mathrm{aq}\right)+{\left({\mathrm{NH}}_4\right)}_2{\mathrm{SO}}_4(\mathrm{s})$
• $\mathrm{Cu}(\mathrm{OH}{)}_2\left(\mathrm{aq}\right)+{\left({\mathrm{NH}}_4\right)}_2{\mathrm{SO}}_4(\mathrm{s})+2{\mathrm{NH}}_4\mathrm{OH}(\mathrm{excess}\left)\right(\mathrm{l})⟶\left[\mathrm{Cu}{\left({\mathrm{NH}}_3\right)}_4\right]{\mathrm{SO}}_4(\mathrm{s})+4{\mathrm{H}}_2\mathrm{O}(\mathrm{l})$

Therefore, when ammonium hydroxide solution is added to copper sulphate in excess, deep blue colour soluble complex salt is formed.