Question

Sodium hydroxide solution is added to solution A. A white precipitate is formed which is insoluble in excess sodium hydroxide solution. Name the metal ion present in solution A.

Answer 1

The metal ion present in solution A is aluminium (Al³⁺) ion. Aluminum oxide or hydroxide react with sodium hydroxide solution to form insoluble white precipitate of sodium aluminate.

$$\begin{gathered} \mathrm{Al}{\left(\mathrm{OH}\right)}_3\left(\mathrm{s}\right)+\mathrm{NaOH}\left(\mathrm{aq}\right)\to {\mathrm{Na}}_2{\mathrm{AlO}}_2\left(\mathrm{s}\right)+2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right) \\ \mathrm{Aluminum}\mathrm{hydroxide}\mathrm{Sodium}\mathrm{hydroxide}\mathrm{Sodium}\mathrm{aluminate}\mathrm{Water} \end{gathered}$$