Question

State two relevant observations for each of the following:

(i) Ammonium hydroxide solution is added to copper (II) nitrate solution in small quantities and then in excess.
(ii) Ammonium hydroxide solution is added to zinc nitrate solution in minimum quantities and then in excess.

Answer 1

(i) Ammonium hydroxide solution added to copper (II) nitrate solution:

• When ammonium hydroxide solution is added to copper (II) nitrate solution in small quantity then a pale blue precipitate of copper (II) hydroxide is formed. The reaction is as follows :
• $\mathrm{Cu}{\left({\mathrm{NO}}_3\right)}_2+2{\mathrm{NH}}_4\mathrm{OH}\to \mathrm{Cu}{\left(\mathrm{OH}\right)}_2\downarrow +2{\mathrm{NH}}_4{\mathrm{NO}}_3$
  (Copper(II) (Ammonium (Copper(II) (Ammonium
  nitrate) hydroxide) hydroxide) nitrate)
  pale blue ppt.
• When ammonium hydroxide solution is added to copper (II) nitrate solution in excess then, the pale blue precipitate turns into a deep blue solution of Tetraammine copper(II) nitrate.

(ii) Ammonium hydroxide solution added to zinc nitrate solution:

• When ammonium hydroxide is added in small quantities, a gelatinous white precipitate of $\mathrm{Zn}{\left(\mathrm{OH}\right)}_2$ is formed.
• When it is added in excess amount, the precipitate dissolves and forms a clear solution.