Question

Explain why a solution of hydrogen chloride in water turns blue litmus red and conducts electricity, while a solution of the same gas in toluene:

1. has no effect on litmus, and
2. does not conduct electricity.

Answer 1

A solution of hydrogen chloride in water gives ions.

\[\ce{HCl + H2O -> H3O+ + Cl-}\]

These ions are responsible for conducting electricity and turning blue litmus red due to the presence of hydronium H₃O⁺ ions, which cause HCl aqueous solution to be acidic.

Toluene is an organic solvent, whereas HCl is a covalent molecule. A solution of HCl in toluene includes only molecules and not ions; hence, it does not conduct electricity. The absence of hydronium H₃O⁺ ions neutralizes the solution, and it has no impact on litmus paper.