Estimating the solubility of 1:1 electrolyte aqueous solutions: the chemical potential difference rule

ABSTRACT

A simple empirical rule to estimate the solubility of force fields of 1:1 aqueous electrolyte solutions at ambient conditions is proposed. The empirical prescription states that the logarithm of the solubility can be described by a second-order polynomial of the chemical potential difference of the salt in the solid and the salt in the standard state in solution. The rule will be denoted as the chemical potential difference rule . It is shown that the recipe is able to provide reasonable values of the solubility of 1:1 aqueous electrolytes (having the NaCl structure in the solid phase) for a number of different force fields for which the solubility has been computed in a rigorous way. This clearly indicates that reproducing only the experimental values of the free energy of hydration of ions at infinite dilution (which yield the standard state chemical potential of the salt in water) is not enough to foresee the experimental values of the solubility. The difference between the chemical potential of the salt in the solid phase and in the standard state seems to be the variable that controls the value of the solubility. This finding should be taken into account in the future when developing force fields for 1:1 electrolytes in water aimed at reproducing the experimental solubilities.

KEYWORDS:

• Solubility
• 1:1 electrolyte aqueous solutions
• simulation

Acknowledgments

It is a pleasure to contribute to this special issue to Prof. Johann Fischer who has contributed so much to our understanding of the liquid state, from theory and simulations, for the bulk and for confined material. One of us (C. Vega) would like to thank him for teaching him Molecular Dynamics in the spring of 1989 in Bochum [77] and for helping him in the early stages of his career. A.L. Benavides thanks support from CONACYT (México) (grant numbers 232832, 152684 and ECOS 232871). This work was funded by the Spanish Ministry of Education [grant numbers FIS2013/43209P and FIS2016-78117P] and by UCM/Santander grant 910570.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

Consejo Nacional de Ciencia y Tecnología CONACYT (México) [grant numbers 232832, 152684 and ECOS 232871]; Spanish Ministry of Education [grant numbers FIS2013/43209P and FIS2016-78117P]; UCM/Santander [grant number 910570].