Tuesday, April 16, 2013

Calculating pH of a monoprotic weak acid solution

Monoprotic weak acids (HA) such as acetic acid do not ionize completely in water. They partially dissociate into hydrogen (hydronium) ions (H+) and the corresponding conjugate base (A-). To calculate the pH of a monoprotic weak acid solution we need to know the concentration of the acid , C, in Molar units and its Ka (acid dissociation constant). The following equation can be applied to calculate the pH.

For example if we have a solution with 0.1 M acetic acid which has  Ka = 1.76 E-5 (1.76 * 10 to the minus 5) then applying the above equation results in pH = 2.88.

The following site has an online pH calculator:


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