Simultaneous determination of equivalence volumes and thermodynamic acid dissociation constants from data for the acidic region of potentiometric titration curves

Abstract

New iterative methods for the analysis of potentiometric titration data of weak monoprotic acids or of mixtures of two monoprotic acids are presented. These methods, using equations without approximations and data exclusively resulting from the acidic region of the titration curve, seem to be valid throughout the acidic strength range. In the titration of weak monoprotic acids, the proposed procedures are able to extract accurate values of the equivalence volume and also the thermodynamic dissociation constant. On the other hand, in the titration of mixtures of two monoprotic acids, the proposed approach is able to extract accurate values of the concentrations and the thermodynamic dissociation constants of the component acids even when their acidity strengths are similar. The test of the proposed procedures by means of ideal simulated data (free from any extraneous “noise”) and Monte Carlo simulated data revealed that these methods are fairly applicable even when the titration data are considerably obscured by “noise”. Further, for acids having p K ≥4 the proposed procedures lead to accurate results even when the pH data contain an important systematic error. The proposed procedures were also successfully applied to experimental titration data for weak acids. A procedure for the analysis of titration data carried out in binary water-dimethylformamide solvent systems is also presented.