On the correlation between bi-ionic potential and the composition of counterions in liquid membranes. I.

Abstract

Bi-ionic potentials were measured as a function of the mole fraction of a counterion in a membrane where the total concentration of the carrier or site (hexadecyl pyridinium ion) was kept constant. The membranes used were prepared by dissolving two hexadecyl pyridinium salts, each with a different counterion, in nitrobenzene. When chloride ion was the only counterion, all bi-ionic systems showed a potential as expected from an equation derived in a previous paper. The order of selectivity in the system was perchloride > thiocyanate > nitrate > bromide > chloride. It was found that the additivity rule for bi-ionic potentials held when the counterion in the membrane was either the same as that in both external aqueous electrolyte solutions, or a less selective one. However, when two different counterions coexisted in the membrane, the membrane potential showed a strong dependence upon the counterion composition. These phenomena were interpreted in terms of the membrane equation by taking into account the boundary potentials. A detailed discussion of the results will be given in this paper.