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 cation–anion interaction in a salt solution. For example, the fitted radii of Li+ and Na+ in LiClO3 and NaClO3 indicate that Li+ is strongly hydrated and has a weak interaction with the ClO3− 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.

中文翻译：

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浓盐溶液的活度系数：蒙特卡罗调查

Monte Carlo (MC) 模拟用于计算浓缩电解质和高温下的单离子和平均离子活度系数和水活度。通过使用依赖于浓度的介电常数，MC 方法的适用范围扩展到 3 mol·L-1 或更高，具体取决于盐。通过仅调整一个参数，即阳离子半径，将计算出的活度系数与实验数据拟合。通过这种方法获得的拟合离子半径表明盐溶液中阳离子-阴离子相互作用的程度。例如，LiClO3 和 NaClO3 中 Li+ 和 Na+ 的拟合半径表明 Li+ 是强水合的，与 ClO3− 离子的相互作用较弱，而 Na+ 形成离子对并失去其水合。HCl 中质子和氯离子的单离子活度系数通过 MC 模拟计算，并与离子选择性电极获得的实验值进行比较。计算出的质子和氯离子的单离子活度系数分别比实验值低得多和高得多。然而，通过 MC 模拟、离子选择性电极和蒸汽压测量获得的 HCl 的平均活度系数非常一致。在 NaCl 和 KCl 的情况下，计算出的 Na+、K+ 和 Cl- 的单离子活度系数更接近于离子选择性电极获得的值。HCl 中的结果表明水合质子很大并且在水合壳内包括氯离子，即氯离子的表观尺寸可以忽略不计。