Question

(a) Give three uses of ammonium chloride.
(b) Why is ammonium hydroxide used in qualitative analysis? Give two equations to justify your answer.

Answer 1

(a) Uses of ammonium chloride:
(i) ​It is used in Leclanche and dry cells.
(ii) It is used in medicine, dyeing, etc.
(iii) It is used as a laboratory reagent.

(b) Ammonium hydroxide is used in qualitative analysis, as it forms different coloured precipitates in the presence of different metal ions. For example, we can use ammonium hydroxide to distinguish if iron is present in a divalent or trivalent state in a given compound, as shown below.

$$\begin{gathered} {\mathrm{FeSO}}_4+2{\mathrm{NH}}_4\mathrm{OH}\to {\left({\mathrm{NH}}_4\right)}_2{\mathrm{SO}}_4+\mathrm{Fe}{\left(\mathrm{OH}\right)}_2\{\mathrm{Dirty}\mathrm{green}\mathrm{precipitate}\mathrm{with}{\mathrm{Fe}}^{2+}\} \\ {\mathrm{Fe}}_2{\left({\mathrm{SO}}_4\right)}_3+6{\mathrm{NH}}_4\mathrm{OH}\to 3{\left({\mathrm{NH}}_4\right)}_2{\mathrm{SO}}_4+2\mathrm{Fe}{\left(\mathrm{OH}\right)}_3\{\mathrm{Reddish}\mathrm{brown}\mathrm{precipitate}\mathrm{with}{\mathrm{Fe}}^{3+}\} \end{gathered}$$