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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 pKa value of 4.76. Its conjugate base is acetate (CH3COO−). A 1.0 M solution (about the concentration of domestic vinegar) has a pH of 2.4, indicating that merely 0.4% of the acetic acid molecules are dissociated. However, in very dilute (&lt; 10−6 M) solution acetic acid is &gt;90% dissociated.