Question

State why dilute hydrochloric acid cannot be concentrated beyond a certain concentration on boiling?

Answer 1

Hydrochloric acid forms a constant boiling mixture, known as an azeotrope, at a concentration of 22.2% HCl by weight (boiling at 109.8°C). Beyond this point, when boiled, both the acid and water vaporize together in the exact same ratio, meaning the concentration cannot be increased further by simple boiling.