Question

Write the observation and balanced equations for the following reactions :
Ammonium hydroxide is added first in a small quantity and then in excess to a solution of copper sulphate.

Answer 1

• A pale blue ppt. develops when Ammonium hydroxide (${\mathrm{NH}}_4\mathrm{OH}$) is added drop by drop to a copper sulphate solution, which dissolves in excess of ${\mathrm{NH}}_4\mathrm{OH}$to create a deep blue or inky blue solution, i.e. Tetraamminecopper(II) sulphate.
• Chemical equation:

$$\begin{gathered} {\mathrm{CuSO}}_4\left(s\right)+2{\mathrm{NH}}_4\mathrm{OH}\left(l\right)\to \mathrm{Cu}(\mathrm{OH}{)}_2\left(s\right)+{\left({\mathrm{NH}}_4\right)}_2{\mathrm{SO}}_4(s\left) \\ \mathrm{Cu}\right(\mathrm{OH}{)}_2\left(s\right)+{\left({\mathrm{NH}}_4\right)}_2{\mathrm{SO}}_4\left(s\right)+2{\mathrm{NH}}_4\mathrm{OH}\left(l\right)\to \left[\mathrm{Cu}{\left({\mathrm{NH}}_3\right)}_4\right]{\mathrm{SO}}_4\left(s\right)+4{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right) \\ \mathrm{Deep}\mathrm{blue} \end{gathered}$$