Dissociation of acids
Let’s look at the dissociation of a common acid – hydrochloric acid or HCl. When HCl molecules dissolve they dissociate into H+ ions and Cl- ions.
HCl is a strong acid because it dissociates almost completely.
By contrast, a weak acid like acetic acid (CH3COOH) does not dissociate well in water – many H+ ions remain bound-up within the molecule.
Acids are sometimes referred to as H+ ion donors because they release H+ ions in solution for other molecules to bind to.