Question

What happens when
(a) NH₃ solution is added to CuSO₄ solution drop by drop and then in excess.
(b) Caustic soda solution is added to Cu(NO₃)₂ solution and product boiled.
(c) Common salt solution added to silver nitrate solution and NH₃ solution added to it.
(d) Lead nitrate solution treated with calcium chloride solution and products are heated and cooled.

Answer 1

(a) When ammonia solution is added to CuSO₄ drop by drop, a blue precipitate of copper hydroxide is formed. Then, when excess ammonia solution is added, the precipitate dissolves and a deep inky-blue liquid of tetramine copper (II) is formed.

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

(b) When caustic soda solution is added to copper nitrate, they react to form sodium nitrate and copper hydroxide, which is a light blue precipitate.

$$\begin{gathered} \mathrm{Cu}{\left({\mathrm{NO}}_3\right)}_2+2\mathrm{NaOH}\to \mathrm{Cu}{\left(\mathrm{OH}\right)}_2+2{\mathrm{NaNO}}_3 \\ \mathrm{Blue}\mathrm{precipitate} \end{gathered}$$

(c) When common salt is added to silver nitrate solution, a white precipitate of silver chloride is formed. Upon addition of NH₃ solution, the precipitate dissolves leaving behind a clear solution.

$$\begin{gathered} {\mathrm{AgNO}}_3+\mathrm{NaCl}\to \mathrm{AgCl}+{\mathrm{NaNO}}_3 \\ \mathrm{White}\mathrm{precipitate} \\ \mathrm{AgCl}+4{\mathrm{NH}}_4\mathrm{OH}\to \left[\mathrm{Ag}{\left({\mathrm{NH}}_3\right)}_4\right]\mathrm{Cl}+4{\mathrm{H}}_2\mathrm{O} \\ \mathrm{Clear}\mathrm{solution} \end{gathered}$$

(d) When lead nitrate solution is treated with calcium chloride, they react to form lead chloride and calcium nitrate. Lead chloride emerges from the solution as a white coloured precipitate.

$$\begin{gathered} \mathrm{Pb}{\left({\mathrm{NO}}_3\right)}_2+{\mathrm{CaCl}}_2\to {\mathrm{PbCl}}_2+\mathrm{Ca}{\left({\mathrm{NO}}_3\right)}_2 \\ \mathrm{White}\mathrm{precipitate} \end{gathered}$$