Strong acids
The acids that release H+ ions by complete ionization in aqueous medium are strong acids. It means that all such acid molecules are dissociated into H+ ions and the corresponding negative ions in water. For example, in an aqueous solution of hydrochloric acid which is a strong acid, there are only H+ ions and Cl- ions but no free HCl molecules.
Weak acids
The acids which release H+ ions in aqueous medium by incomplete or partial ionization are called weak acids. This means that in aqueous medium, only a fraction of such acid molecules are dissociated into H+ ions and relevant negative ions. The unionized molecules remain as molecules themselves in aqueous solution.
