Studies with Model Membrane: Determination of Fixed Charge Density of Silver Sulfite Membrane

Abstract

Parchment-supported silver sulfite membrane has been prepared by the interaction method. The membrane potential across the membrane in contact with different 1:1 electrolytes has been measured. The experimentally measured membrane potential values were used to evaluate the thermodynamically effective fixed charge density of the membrane-electrolyte systems using Teorell, Meyer, and Sievers (T. M. S.), Altug and Hair, and Kobatake et. al. theories. The values of effective charge densities were quite low (they were in order of 10-2 – 10-3 eq/l) and hence very difficult to determine by usual exchange methods. The values of effective charge densities by different theories were the same order of magnitude for each membrane-electrolyte system. The theoretical predictions for membrane potential were borne out quite satisfactorily by experimental results obtained with the membranes. Apparent transference numbers of coions and permselectivity values of the membrane-electrolytes have also been calculated. A method based on permselectivity values for determination of charge density was also used. It was interesting to note that the charge densities evaluated from two methods of Kobatake and co-workers gave similar values and that the results were comparable to those derived from the TMS method.