Question

Why can not $\mathrm{HCl}$ be dried over quicklime or ${\mathrm{P}}_4{\mathrm{O}}_{10}$.

Answer 1

• When an acid reacts with a base it will produce salt and water. This is called a neutralization reaction.
• $\mathrm{HCl}$ can not be dried over quicklime $\left(\mathrm{CaO}\right)$ or ${\mathrm{P}}_4{\mathrm{O}}_{10}$ because $\mathrm{HCl}$ is acidic in nature whereas $\mathrm{CaO}$ is basic in nature so if we use $\mathrm{CaO}$ for drying, both will react to form a salt.

$$\begin{gathered} 2\mathrm{HCl}\left(\mathrm{aq}\right)+\mathrm{CaO}\left(\mathrm{s}\right)\to {\mathrm{CaCl}}_2\left(\mathrm{aq}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right) \\ 12\mathrm{HCl}\left(\mathrm{aq}\right)+{\mathrm{P}}_4{\mathrm{O}}_{10}\left(\mathrm{s}\right)\to 4{\mathrm{POCl}}_3\left(\mathrm{aq}\right)+6{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right) \end{gathered}$$

Hence, $\mathbf{HCl}$ can not be dried over quicklime or ${\mathbf{P}}_{\mathbf{4}}{\mathbf{O}}_{\mathbf{10}}$.