Effect of variable relative permittivity on the thermodynamics of asymmetric valency aqueous salts

Abstract

Experimentally determined empirical formulae for the concentration dependent relative permittivity of aqueous solutions of MgCl${}_2$ and NiCl${}_2$ are utilized to calculate the osmotic coefficient and the mean activity coefficient of these salts for a range of concentrations. The systems are modelled using the primitive model of electrolytes and analyzed using the symmetric Poisson-Boltzmann theory, the modified Poisson-Boltzmann theory, the mean spherical approximation, and the Monte Carlo simulations. Generally, the mean spherical approximation and the modified Poisson-Boltzmann theory reproduce the benchmark simulation data well up to $\sim$1.6 mol/dm${}^3$ or more in many instances, while the symmetric Poisson-Boltzmann results show discrepancies starting from $\sim$0.25 mol/dm${}^3$. Both the simulations and the theories tend to deviate from the corresponding experimental results beyond $\sim$1 mol/kg.

arXiv comment15 pages, 9 figures

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