Question

What is the residue left in the test tube when solid Ammonium chloride is strongly heated? Justify your answer with a balanced reaction.

Answer 1

1. When solid Ammonium chloride(${\mathrm{NH}}_4\mathrm{Cl}$) is strongly heated above $340°\mathrm{C}$ in a test tube, it decomposes into Ammonia $\left({\mathrm{NH}}_3\right)$ and Hydrochloric $\left(\mathrm{HCl}\right)$ gas.
2. This change is sometimes referred to as ‘sublimation’.
3. In actual case of sublimation, there is only a change of state and no decomposition.
4. Reaction:$$\begin{gathered} {\mathrm{NH}}_4\mathrm{Cl}\left(\mathrm{s}\right)\stackrel{340°\mathrm{C}}{\to }{\mathrm{NH}}_3\left(\mathrm{g}\right)\uparrow +\mathrm{HCl}\left(\mathrm{g}\right)\uparrow \\ (\mathrm{Ammonium}\mathrm{chloride})\left(\mathrm{Ammonia}\right)(\mathrm{Hydrogen}\mathrm{chloride}) \end{gathered}$$.
5. Therefore, when Ammonium chloride(${\mathrm{NH}}_4\mathrm{Cl}$) is strongly heated it decomposes into two gases, Ammonia gas and Hydrochloric gas and hence there is no residue left in test tube.