Depending on the experiment of Helkamp and Johnson, apparent pKa was obtained by determining the pH at titrating of one half for unknown acid which is water soluble acid. We have found a mathematical method to obtain the absolute constant.

• 本文依据Helmkamp和Johnson所提出的实验方法，通过选择易溶于水的弱酸，采用电位滴定法准确测定滴定HA至一半时溶液的氢离子浓度，得到表观离解常数pKa，并通过数学方法计算出绝对pKa。