Acid―base properties of ion exchangers. Ⅱ. Determination of the acidity parameters of ion exchangers with arbitrary functionality

摘要

A method for determination of the acidity parameters of ion exchangers with arbitrary functionality from poten-tiometric titration data was developed. Titration of ion exchanger RH (ROH) with alkali KtOH or acid HAn is considered as superposition of ion exchange H~+-Kt~+(OH~-―An~-) and the reaction of neutralization. The method is based on the assumption of linear dependence of logarithm of the equilibrium coefficient of the ion exchange as a function of the neutralization degree. The acidity parameters are two constants of this dependence. They are ther-modynamic equilibrium constant of ion exchange, pK and the difference between logarithm of the equilibrium coefficient at the complete and zeroth neutralization of the ion exchanger, Δpk. Specially developed computer program allows reconstruction of the potentiometric titration curve from the sets of the acidity parameters of each type of the functional groups in the resin. The theory was tested on a number of ion exchangers with different functionalities: sulfonic and carboxylic acid cation exchangers, polyfunctional weak base anion exchangers of different structures. The ion exchange capacity of each type of groups can be determined with precision higher than 0.1 meq/g. The pK_i values of the groups present in macroamounts are determined with precision at least +-0.2 pK units.