Why a dilute aqueous solution of hydrochloric acid cannot be concentrated by evaporation beyond 22.2%?

Explanation

A soution of hydrogen chloride in water which contains 22.2% HCI (by weight) forms a constant boiling mixture having boiling point 382.8 K. At 382.8 K, the water and HCI gas escape together and there is no change in the composition of the solution. Dilute HCl, therefore, cannot be concentrated by evaporation beyond 22.2%.