Question

What is the difference between dilute `HCl` and liquid `HCl`?

Answer 1

One is a solution of a strong acid, the other is just a liquid (no acidic properties).

Explanation:

Liquified HCl has been cooled until the gas turns to a liquid, in the same way most other gases change on cooling. It is a pure substance in the liquid phase.

"Dilute" HCl implies you have dissolved a small amount of HCl gas into water. In this case, an ionization reaction occurs as follows:

`HCl (aq) + H_2O rarr H_3O^+ + Cl^-`

This is a complete reaction (hence HCl is a strong acid), and the resulting hydronium ion, `H_3O^+` gives the solution acidic properties.

Liquid HCl does not display these properties, as no reaction with `H_2O` occurs.