Question

State the effect of adding a small amount of: (a) sodium hydroxide (b) ammonium hydroxide followed by an excess in each case to samples of each of the salt solutions.
(i) calcium nitrate [small amount .......... in excess ..........].
(ii) zinc nitrate [small amount ........... in excess ............].
(iii) lead nitrate [small amount ........... in excess .........].

Answer 1

Following reactions occur when sodium hydroxide is added to the below mentioned compounds:
(i) Calcium nitrate [in small amount - a white precipitate formed; in excess - the precipitate does not dissolve]

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

(ii) Zinc nitrate [in small amount - a white precipitate formed; in excess - the precipitate dissolves]

$$\begin{gathered} \mathrm{Zn}{\left({\mathrm{NO}}_3\right)}_2+2\mathrm{NaOH}\to \mathrm{Zn}{\left(\mathrm{OH}\right)}_2+2{\mathrm{NaNO}}_3 \\ \mathrm{White}\mathrm{precipitate} \\ \mathrm{Zn}{\left(\mathrm{OH}\right)}_2+2\mathrm{NaOH}\left(excess\right)\to {\mathrm{Na}}_2\left[\mathrm{Zn}{\left(\mathrm{OH}\right)}_4\right] \end{gathered}$$

(iii) Lead nitrate [in small amount - a white precipitate formed; in excess - the precipitate dissolves]

$$\begin{gathered} \mathrm{Pb}{\left({\mathrm{NO}}_3\right)}_2+2\mathrm{NaOH}\to \mathrm{Pb}{\left(\mathrm{OH}\right)}_2+2{\mathrm{NaNO}}_3 \\ \mathrm{White}\mathrm{precipitate} \\ \mathrm{Pb}{\left(\mathrm{OH}\right)}_2+2\mathrm{NaOH}\left(\mathrm{excess}\right)\to {\mathrm{Na}}_2\left[\mathrm{Pb}{\left(\mathrm{OH}\right)}_4\right] \end{gathered}$$

Following reactions occur when ammonium hydroxide is added to the below mentioned compounds:
(i) Calcium nitrate [in small amount - no precipitate formed; in excess - no change]

$$\begin{gathered} \mathrm{Ca}{\left({\mathrm{NO}}_3\right)}_2+2{\mathrm{NH}}_4\mathrm{OH}\to \mathrm{Ca}{\left(\mathrm{OH}\right)}_2+2{\mathrm{NH}}_4{\mathrm{NO}}_3 \\ \mathrm{White}\mathrm{precipitate} \end{gathered}$$

(ii) Zinc nitrate [in small amount - a gelatinous white precipitate is formed; in excess - the precipitate dissolves]

$$\begin{gathered} \mathrm{Zn}{\left({\mathrm{NO}}_3\right)}_2+2{\mathrm{NH}}_4\mathrm{OH}\to \mathrm{Zn}{\left(\mathrm{OH}\right)}_2+2{\mathrm{NH}}_4{\mathrm{NO}}_3 \\ \mathrm{Gelatinous}\mathrm{White}\mathrm{precipitate} \\ \mathrm{Zn}{\left(\mathrm{OH}\right)}_2+2{\mathrm{NH}}_4{\mathrm{NO}}_3+2{\mathrm{NH}}_4\mathrm{OH}\left(\mathrm{excess}\right)\to \left[\mathrm{Zn}{\left({\mathrm{NH}}_3\right)}_4\right]{\left({\mathrm{NO}}_3\right)}_2+4{\mathrm{H}}_2\mathrm{O} \end{gathered}$$

(iii) Lead nitrate [in small amount - a white precipitate is formed; in excess - the precipitate does not dissolve]

$$\begin{gathered} \mathrm{Pb}{\left({\mathrm{NO}}_3\right)}_2+2{\mathrm{NH}}_4\mathrm{OH}\to \mathrm{Pb}{\left(\mathrm{OH}\right)}_2+2{\mathrm{NH}}_4{\mathrm{NO}}_3 \\ \mathrm{White}\mathrm{precipitate} \end{gathered}$$