Activity Coefficients of Concentrated Salt Solutions: A Monte Carlo Investigation

Abstract

Monte Carlo (MC) simulations were used to calculate single ion and mean ionic activity coefficients and water activity in concentrated electrolytes and at elevated temperatures. By using a concentration dependent dielectric constant, the applicability range of the MC method was extended to 3 mol·L −1 or beyond, depending on the salt. The calculated activity coefficients were fitted to experimental data by adjusting only one parameter, i.e., the cation radius. Fitted ionic radii obtained by such a procedure indicate the extent of cationanion interaction in a salt solution. For example, the fitted radii of Li + and Na + in LiClO 3 and NaClO 3 indicate that Li + is strongly hydrated and has a weak interaction with the ClO 3 − ion whereas Na + forms ion pairs and loses its hydration. The single ion activity coefficients for protons and chloride ions in HCl were calculated by MC simulations and compared with experimental values obtained by ion selective electrodes. The calculated single ion activity coefficients for protons and chloride ions are much lower and higher, respectively, than the experimental values. However, the mean activity coefficients of HCl obtained by the MC simulations, ion selective electrodes and vapor pressure measurements are in good agreement. In the case of NaCl and KCl the calculated single ion activity coefficients of Na + , K + , and Cl − are much closer to the values obtained by ion selective electrodes. The results in HCl indicate that the hydrated proton is large and includes the chloride ion within the hydration shell, i.e., the apparent size of the chloride ion is negligible.

Individual Ion Activity Coefficients in Aqueous Electrolytes from Explicit-Water Molecular Dynamics Simulations

“…58 Furthermore, they considered a concentration-dependent ε r with a polynomial function fitted to experimental data. In a more recent study, Abbas and Ahlberg 59 used MC simulations with the PM to calculate the IIACs and MIACs of several aqueous salts at elevated temperatures, with a concentration-dependent ε r , adopted from the study by Buchner et al 60 Although implicit-water simulations are computationally inexpensive, they do not include information on the solution structure and ion hydration. Despite obtaining reasonable agreement between MIAC values from implicit-water simulations and experiments, they typically underestimate the chemical potentials by several orders of magnitude.…”

“…Furthermore, they considered a concentration-dependent ε r with a polynomial function fitted to experimental data. In a more recent study, Abbas and Ahlberg used MC simulations with the PM to calculate the IIACs and MIACs of several aqueous salts at elevated temperatures, with a concentration-dependent ε r , adopted from the study by Buchner et al…”

Traceable Values for Activity and Osmotic Coefficients in Aqueous Sodium Chloride Solutions at Temperatures from 273.15 to 373.15 K up to the Saturated Solutions

“…A second family of models is based upon the equation of state and includes, for example, the perturbed-chain-statistical-associated-fluid-theory. , In the conductor-like-screening-model with segment-activity-coefficients approach the molecular surface area is subdivided into charged segments that interact with each other . Recent studies have demonstrated that one can also use Monte Carlo and molecular dynamical modeling to calculate the activity and osmotic coefficients in NaCl solutions. − …”

Predictive Thermodynamic Model for Intrusion of Electrolyte Aqueous Solutions in Nanoporous Materials

“…Consequently, this approach has the same limitation as that for the Gibbs ensemble MC method to be used in combination with atomistic force fields. Also, another straightforward approach used a modified Widom insertion method 81 to compute the activity coefficient of electrolyte, but in implicit water solvation making it unsuitable for atomistic force field either. Theoretical models based on experimental thermodynamic data are alternative approaches to predict vapor pressure (and, by extension, activity of water) in electrolyte solutions.…”