A theoretical treatment of cation exchangers - II. Equilibria between an ion exchanger and an aqueous solution with a common cation

Abstract

The treatment of an ion exchanger as a concentrated aqueous poly-electrolyte is extended to cover the case of an exchanger saturated with a single cation which is in equilibrium with a solution containing a salt of the same cation. For this purpose equations are derived for the activity and osmotic coefficients of mixtures of 1:1 electrolytes with resinates giving only one mobile ion per equivalent. Applying these equations to experimental data, values of the 'Harned' coefficients α 12 and α 21 are calculated. From these the absolute value of the activity coefficient of the H-resinate (using infinite dilution as the standard state) is deduced, which, taken in conjunction with the osmotic data of part I, enable the activity coefficient curve to be obtained, up to very high concentrations. This curve shows that at high concentrations there is less ion-pair formation for ‘resinates’ of the sulphonated polystyrene type than is shown in aqueous solutions of the corresponding nitrates at the same ionic strength.