Question

Dry hydrogen chloride gas does not turn blue litmus to red whereas hydrochloric acid does. Why?

Answer 1

Hydrochloric acid$\left(\mathrm{HCl}\right)$:

• $\mathrm{HCl}$ is a polar covalent compound and is considered a strong acid in an aqueous solution.
• Acids give a litmus test by producing ${\mathrm{H}}^{+}$ ions in an aqueous solution.
• $\mathrm{HCl}$ being a strong acid dissociates completely and produces ${\mathrm{H}}^{+}$ ion in an aqueous solution which turns blue litmus red.
• But, $\mathrm{HCl}$ gas does not give any ${\mathrm{H}}^{+}$ ion so it does not act as an acid. so it does not give a litmus test.