Acidity of Solutions of Strong Bases

James Richard Fromm

A strong base, like a strong acid, is virtually totally dissociated in water; thus 0.01 molar NaOH is actually an aqueous solution 0.01 molar in Na+ and also 0.01 molar in OH-. The sodium ions have a negligible effect on the pH, which is determined by the hydroxide ion concentration. It is often more convenient to calculate the pH of basic solutions by first calculating the pOH as is done in the following example.

Example. The pH of 0.01 molar aqueous NaOH solution is calculated as follows: [OH-] = 0.01; pOH = 2, pH + pOH = pKw = 14, so pH = 12.

As in the case of an aqueous solution of a strong acid, the contribution from the autoionization of water is almost always negligible. In an aqueous solution of a strong base, acidity is essentially determined by the concentration of the strong base alone.

Copyright 1997 James R. Fromm