Theory of Gas Solubility and Hydrophobic Interaction in Aqueous Electrolyte Solutions

Ion-specific effects on the solubility of nonpolar solutes and on the solute–solute hydrophobic interaction in aqueous electrolyte solutions are studied on the basis of a continuum theory that incorporates the excluded volume of the molecules using the four-component (water, cations, anions, and solutes) Boublı́k–Mansoori–Carnahan–Starling–Leland model and ion hydration (electrostriction) using the Born model. We examine how the ordering of ions in the salt effect on the solubility as measured by the Sechenov coefficient KS changes with varying sizes of ions and solutes. Our calculation reproduces the general trend of experimentally measured KS and also provides insight into the irregular behavior of KS for lithium ion. The correlation between KS and the salt effect on the hydrophobic interaction that has been pointed out earlier is accounted for by an explicit connection between KS and the salt-enhanced-association coefficient CI in the expansion of the second osmotic virial coefficient B(ns) = B(0) – CIns + ··· in powers of the salt density ns at fixed pressure and temperature. The quadratic relation is derived for ions and solutes that are not very large.

This document is the Accepted Manuscript version of a Published Work that appeared in final form in The Journal of Physical Chemistry B, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/acs.jpcb.1c08050 .