平均球近似法计算电解质活度系数的研究(Ⅰ)——单一电解质水溶液

对平均球近似(MSA)的原始模型进行研究,提出了阳离子有效直径随溶液中离子浓度变化的关系式.用原MSA模型、Pitzer模型和本文改进后的模型对85个单一电解质水溶液(最大浓度达34.12mol/kg)的离子平均活度系数进行了计算和比较,结果表明作者改进的模型精度最高.另外,用298.15K回归出的参数预测其它温度下的离子平均活度系数,与Bromley、Meissner、Chen和Pitzer4个模型进行比较,本文模型的计算结果最好,说明本文的模型参数与温度关系较小.

CALCULATION OF ACTIVITY COEFFICIENTS BY USING MEAN SPHERICAL APPROXIMATION ( I )FOR SINGLE ELECTROLYTE AQUEOUS

The effective diameter of a cation is introduced into the mean spherical approximation(MSA)method. The ionic strength dependence of effective diameter is attributed to the effect of solvation mainly. The effective diameter parameters of the cations have been obtained from regression of the mean ionic activity coefficient data. The range of concentration extends up to saturation when data are available. The modified model has been used to correlate the mean ionic activity coefficients for 85 single electrolyte solutions. The calculated results of the modified mean spherical approximation, original MSA model and Pitzer model are compared with the experimental data. It shows that the modified mean spherical approximation model gives the best representation. The modified mean spherical approximation model has been used to predict the mean ionic activity coefficients at other temperatures by using the parameters obtained at 298.15K. The calculated data show that the temperature dependence of the parameters in this model is smaller than that in the other four models (Pitzer, Bromley, Meissner and Chen).