Theory of titration curves: Locations of points at which ph=pk a on potentiometric acid-base titration curves; end-point errors in titrations to predetermined ph values

Abstract

For the titration of a pure solution of a weak monobasic acid with a strong base, it is shown that the fraction of the equivalent volume of base added at the point where pCH = p K α is exactly equal to 1 2 if and only if p K α = p K ω 2 , in which case it is independent of dilution. It is less than 1 2 if p K α < p K ω 2 and is greater than 1 2 if p K α > p K ω 2 , and in either of these cases it depends on the concentrations of both acid and base. Explicit descriptions are given of the conditions under which pcH = p K α either at the start of the titration or at the equivalence point. For the titration of either a weak or a strong acid with a strong base, exact equations are given for the titration error resulting from the termination of the titration at any preselected pcH value.