QUANTITATIVE PRESENTATION OF POTENTIOMETRIC TITRATION CURVES OF ION-EXCHANGERS

Neutralization of ion exchangers in H+ or OH- forms by alkali M(OH)(2) 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 equati on connecting pH and the external electrolyte concentration with the i on exchanger neutralization degree was derived. It can be used for pre sentation of the potentiometric titration curves in mathematical form or their calculation at different (not necessarily constant) concentra tions of external electrolyte. Applicability of the modified Henderson -Hasselbach equation as one of the possible means for description of p otentiometric titration curves of ion exchangers was also discussed. T he range of its applicability and limitations were established. The ph ysical meaning of its constants was clarified, and the equations of th eir relations with the apparent ion exchange equilibrium constant have been obtained. The theoretical considerations are illustrated with th e example of potentiometric titration curves of a carboxylic acid ion exchanger obtained in a wide range of degrees of neutralization and ex ternal electrolyte concentrations.