Acidity

The hydrogen center in the carboxyl group (−COOH) in carboxylic acids such as acetic acid can separate from the molecule by ionization:

CH₃CO₂H → CH₃CO₂^- + H⁺

Because of this release of the proton (H⁺), acetic acid has acidic character. Acetic acid is a weak monoprotic acid. In aqueous solution, it has a pK_a value of 4.76. Its conjugate base is acetate (CH₃COO⁻). A 1.0 Msolution (about the concentration of domestic vinegar) has a pH of 2.4, indicating that merely 0.4% of the acetic acid molecules are dissociated.

Source: Wikipedia.com