Abstract In the teaching of University Chemistry, there are diverse versions in different textbooks about calculation condition of the hydrogen ions concentration in polybasic weak acid solutions. This brings much confusion to the teaching of teachers and the learning of students. The calculation condition with relative versatility was selected through discussing Ka1/Ka2 of polybasic weak acids to determine whether the hydrogen ions dissociated by the second dissociation of polybasic weak acids could be ignored. The discussion was based on the allowed relative error of the simplist calculating formula of the hydrogen ions concentration of weak acids. The calculation strategy with general applicability based on charge balance equation was also discussed.
