MEAN AND SINGLE ION ACTIVITY-COEFFICIENTS IN AQUEOUS MIXTURES OF SODIUM-CHLORIDE AND SODIUM PECTATE, SODIUM PECTINATE, AND SODIUM CARBOXYMETHYLCELLULOSE

Mean ion, counterion, and co-ion activity coefficients in aqueous solutions of sodium pectate (ξ = 163) sodium carboxymethylcellulose (ξ = 1.19), and sodium pectinates (ξ = 1.20, 0.97, 0.82, and 0.25) with added sodium chloride are reported Measurements were carried out by an electrochemical cell method with Na-glass, Ag/AgCl, and calomel electrodes. Two different polyelectrolyte concentrations (mp = 0.0100,0.0250 mol/kg of H2O)were studied and at a given polyelectrolyte concentration the ratio of polyelectrolyte to salt concentration was varied from 0.1 to 57. In all systems studied, the co-ion activity coefficient is considerably larger than the counterion activity coefficient. The results are compared to the predictions of Manning's limiting law for activities and of new limiting laws developed by Iwasa et al. The reported difference between co-ion and counterion activity coefficients even for polyions with low charge densities is consistent with the prediction of new limiting laws. © 1979 American Chemical Society.