Question

why dilute HCl cannot be concentrated beyond a certain concentration of boiling

Answer 1

Dilute HCl is formed by passing anhydrous HCl gas into water to a certain extent. The HCl in the acid develops a weight percentage with water [ approx. 22% - which means that for every 1ml of acid 0.22 is HCl] that would evaporate with the water in the same weight percentage [which means that if 1ml of the acid is evaporated, 0.22ml of HCl goes with it]

This is why HCl cannot be concentrated to a certain extent of boiling