Question

Three test tubes contain calcium nitrate solution, zinc nitrate solution and lead nitrate solution respectively. Each solution is divided into two portions (i) and (ii). Describe the effect of
(i) adding sodium hydroxide solution to each portion in turn till it is in excess.
(ii) adding ammonium hydroxide to each portion in turn till it is in excess.

Answer 1

(i)

Action of sodium hydroxide solution
Calcium nitrate solution	Zinc nitrate solution	Lead nitrate solution
Calcium nitrate solution reacts with sodium hydroxide solution to form white precipitate of calcium hydroxide, which on further addition of excess sodium hydroxide is sparingly soluble. $\mathrm{Ca}{\left({\mathrm{NO}}_3\right)}_2+2\mathrm{NaOH}\to \mathrm{Ca}{\left(\mathrm{OH}\right)}_2+{\mathrm{NaNO}}_3$	Zinc nitrate solution reacts with sodium hydroxide solution to form white gelatinous precipitate of zinc hydroxide, which on further addition of excess sodium hydroxide forms soluble, complex sodium zincate. $$\begin{gathered} \mathrm{Zn}{\left({\mathrm{NO}}_3\right)}_2+2\mathrm{NaOH}\to \mathrm{Zn}{\left(\mathrm{OH}\right)}_2+{\mathrm{NaNO}}_3 \\ \mathrm{Zn}{\left(\mathrm{OH}\right)}_2+2\mathrm{NaOH}\to {\mathrm{Na}}_2{\mathrm{ZnO}}_2+2{\mathrm{H}}_2\mathrm{O} \end{gathered}$$	Lead nitrate reacts with sodium hydroxide solution to form white precipitate of lead hydroxide. Lead hydroxide, being amphoteric in nature, reacts with excess sodium hydroxide solution to form colourless, soluble, complex sodium plumbite and water. $$\begin{gathered} \mathrm{Pb}{\left({\mathrm{NO}}_3\right)}_2+2\mathrm{NaOH}\to \mathrm{Pb}{\left(\mathrm{OH}\right)}_2+{\mathrm{NaNO}}_3 \\ \mathrm{Pb}{\left(\mathrm{OH}\right)}_2+2\mathrm{NaOH}\to {\mathrm{Na}}_2{\mathrm{PbO}}_2+2{\mathrm{H}}_2\mathrm{O} \end{gathered}$$

(ii)

Reaction with ammonium hydroxide
Calcium nitrate solution	Zinc nitrate solution	Lead nitrate solution
Calcium nitrate solution does not react even with excess ammonium hydroxide to form calcium hydroxide. So no reaction takes place between calcium nitrate and ammonium hydroxide.	Zinc nitrate solution reacts with ammonium hydroxide solution to form white gelatinous precipitate of zinc hydroxide. On adding excess of ammonium hydroxide, soluble, colourless tetramine zinc complex is formed. $$\begin{gathered} \mathrm{Zn}{\left({\mathrm{NO}}_3\right)}_2+2{\mathrm{NH}}_4\mathrm{OH}\to \mathrm{Zn}{\left(\mathrm{OH}\right)}_2+2{\mathrm{NH}}_4{\mathrm{NO}}_3 \\ \mathrm{Zn}{\left(\mathrm{OH}\right)}_2+2{\mathrm{NH}}_4\mathrm{OH}+2{\mathrm{NH}}_4{\mathrm{NO}}_3\to \left[\mathrm{Zn}{\left({\mathrm{NH}}_3\right)}_4\right]{\left({\mathrm{NO}}_3\right)}_2+4{\mathrm{H}}_2\mathrm{O} \end{gathered}$$	Lead nitrate solution reacts with ammonium hydroxide solution to form white precipitate of lead hydroxide, which is insoluble in excess of ammonium hydroxide. $\mathrm{Pb}{\left({\mathrm{NO}}_3\right)}_2+2{\mathrm{NH}}_4\mathrm{OH}\to \mathrm{Pb}{\left(\mathrm{OH}\right)}_2+2{\mathrm{NH}}_4{\mathrm{NO}}_3$