Diffusion coupling in associating Non-ideal Multi-Electrolyte solutions

Abstract

A theoretical formalism to describe the diffusion coupling process in multiply non-ideal associating aqueous electrolyte solutions is presented. Association considers complexes formation to arbitrary order. Non-ideality is taken into account with the use of the mean spherical approximation (MSA). The internal electrical field due to the major electrolyte, is calculated using the dynamical electroneutrality condition and the general equations are solved in two ways: (i) a classic finite differences method and (ii) a linearization procedure or normal mode (NM) analysis. This last approximation gives closed analytical relations showing explicitly the coupling between association and non-ideality phenomena. To illustrate both methodologies, new experimental results are presented for the diffusion of an electrolyte mixture of ZnCl, and LiCl where CI” ions and tracer Zn”* ions can associate to form complexes up to Zac” (pentamers). The theoretical results are in good agreement with the experimental data.