Question

What colour precipitates are formed when aqueous ammonia reacts with:
Copper sulphate
State the solubility of each precipitate in excess of ammonium hydroxide.

Answer 1

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

• Ammonium hydroxide$\left({\mathrm{NH}}_4\mathrm{OH}\right)$ (ammonia solution) reacts with copper(II) sulphate solution to form a pale blue colored precipitate of $\mathrm{Cu}(\mathrm{OH}{)}_2$, which dissolves in excess of ammonium hydroxide.
• One mole of copper(II) sulphate reacts with two moles of ammonium hydroxide to form one mole of $\mathrm{Cu}(\mathrm{OH}{)}_2$ and one mole of ${\left({\mathrm{NH}}_4\right)}_2{\mathrm{SO}}_4$.
• ${\mathrm{CuSO}}_4\left(\mathrm{aq}\right)+2{\mathrm{NH}}_4\mathrm{OH}\left(\mathrm{aq}\right)⟶\mathrm{Cu}(\mathrm{OH}{)}_2\left(\mathrm{s}\right)+{\left({\mathrm{NH}}_4\right)}_2{\mathrm{SO}}_4(\mathrm{aq})$

Therefore, pale blue colored precipitate is formed when aqueous ammonia reacts with copper sulphate which dissolves in excess of ammonium hydroxide.