Quantitative Presentation of Potentiometric Titration Curves of Ion Exchangers

Abstract

Neutralization of ion exchangers in H + or OH - forms by alkali M(OH) z or acid H z A was considered as a specific case of ion exchange H + -M z+ or OH - -A z- accompanied by the neutralization reaction. An equation connecting pH and the external electrolyte concentration with the ion exchanger neutralization degree was derived. It can be used for presentation of the potentiometric titration curves in mathematical form or their calculation at different (not necessarily constant) concentrations of external electrolyte. Applicability of the modified Henderson-Hasselbach equation as one of the possible means for description of potentiometric titration curves of ion exchangers was also discussed. The range of its applicability and limitations were established. The physical meaning of its constants was clarified, and the equations of their relations with the apparent ion exchange equilibrium constant have been obtained. The theoretical considerations are illustrated with the example of potentiometric titration curves of a carboxylic acid ion exchanger obtained in a wide range of degrees of neutralization and external electrolyte concentrations.