Question

Liquid HCl is a non-electrolyte but aqueous HCl is a strong electrolyte, explain

Answer 1

Electrolyte substance is that containing many free moving ions. Pure HCl is molecular compound, which can only produce ions by autoionization: HCl + HCl = H2Cl+ + Cl-, which is inferior in liquid HCl because of small equilibrium constant (due to weak Lewis basicity of Cl atoms in HCl). On the contrary, in aqueous solution HCl readily dissociates: HCl + H2O = H3O+ + Cl- and the constant of this equilibrium is very large (due to basic properties of O atoms in H2O). Thus, in aqueous solution there are many ions due to HCl dissociation and protonation of water molecules.