Question

Identify the gas evolved and give chemical test in each of the following:

Dilute Hydrochloric acid reacts with Iron(II) sulphide.

Answer 1

• Dilute Hydrochloric acid ($\mathbf{HCl}$) when added to metal sulphide forms metal chloride and liberates Hydrogen sulphide (${\mathbf{H}}_{\mathbf{2}}\mathbf{S}$) gas with a rotten egg smell.
• General reaction of metal sulphides with dilute Hydrochloric acid is $$\begin{gathered} \mathrm{Metal}+\mathrm{Hydrochloric}\to \mathrm{Metal}+\mathrm{Hydrogen} \\ \mathrm{Sulphide}\mathrm{acid}(dil.)\mathrm{chloride}\mathrm{sulphide} \end{gathered}$$
• Reaction between Iron(II) sulphide ($\mathbf{FeS}$) and Hydrochloric acid is $$\begin{gathered} \mathrm{FeS}\left(\mathit{s}\right)+2\mathrm{HCl}\left(aq\right)\to {\mathrm{FeCl}}_2\left(aq\right)+{\mathrm{H}}_2\mathrm{S}\left(g\right)\uparrow \\ \mathrm{Iron}\left(\mathrm{II}\right)\mathrm{Hydrochloric}\mathrm{Iron}\left(\mathrm{II}\right)\mathrm{Hydrogen} \\ \mathrm{sulphide}\mathrm{acid}\mathrm{chloride}\mathrm{sulphide} \end{gathered}$$
• Therefore, the gas that evolves is Hydrogen sulphide (${\mathbf{H}}_{\mathbf{2}}\mathbf{S}$). It is a colorless gas with a rotten egg smell.