Excess Volume of Mixing of Quaternary Phosphonium Chlorides with Potassium Chloride in Water

Abstract

Abstract Volume changes upon mixing aqueous solutions of potassium chloride and the quaternary phosphonium chloride, n·Bu4−nPhnPCl, (n=0–4), have been measured at various constant total ionic strengths (I=0.25, 0.5, 1.0) at 25 °C. Based on Friedman’s theory for a mixed electrolyte solution, volume-interaction parameters, υo, were determined at each ionic strength. The dependence of υo on I shows that contributions to the excess volume due to structural effects of a pairwise interaction between the cations and triplet interactions including a single anion are most significant for the Bu4P+ ion and decrease with increasing n. A comparison of the υo’s with the excess-volume properties of the salts in each pure solution shows that the interaction between the phosphonium cations and the potassium ion results in negative contributions to the excess volume of mixing, which also decreases as n increases.