Question

(a) Name an element which reacts with hydrogen to form a compound which is strongly acidic in water.
(b) Explain why dilute hydrochloric acid cannot be concentrated by boiling beyond 22.2%.

Answer 1

(a) Chlorine.
The compound formed which is strongly acidic in water is HCl.
$H_2+C{l}_2⟶2HCl$
(b) A dilute aqueous solution of hydrochloric acid gets gradually concentrated on distillation until the concentration of the acid reaches 22.2% HCl by weight which boils at ${110}^{o}C$. When this concentration is reached, no further increase in the concentration of the acid becomes possible by boiling. This is because vapours evolved before ${110}^{o}C$ are vapours of water but at the temperature above ${110}^{o}C$ consist mostly of molecules of HCl.