H2O-C2H5OH-MX(NaCl等)体系中离子缔合和活度

用桥式电路测定了H_2O-C_2H_5OH-NaCl体系的摩尔电导, 并用Lee-Wheaton模型回归出H_2O-C_2H_5OH-NaCl(KCl、CsCl、KBr)体系的离子缔合常数、极限摩尔电导和距离参数, 并求出缔合反应标准自由焓。结果表明离子缔合能力的顺序为Cs~+>K~+>Na~+, Cl~->Br~-, 此四种盐在乙醇中都形成溶剂分开型离子对。并用液上空间气相色谱法测定了水-乙醇-(NaCl、KCl、KBr)体系中溶剂的活度, 用改进的Pitzer-Li公式计算了此体系的活度系数, 计算时考虑了盐在低介电常数溶剂中的离子缔合, 结果表明这种处理是合适的。还表明离子缔合程度随着乙醇浓度上升而加大, 以及盐的存在对水呈盐溶效应而对乙醇呈盐析效应。

ION ASSOCIATION AND ACTIVITY IN H_2O-C_2H_5OH-MX(NaCl etc)SYSTEMS

The conductance bridge was used to measure the molar conductances for H_2O-C_2H_5OH-NaCl system and the headspace gas chromatograph was used to measure theactivity of water and ethanol in H_2O-C_2H_5OH-(NaCl,KCl,KBr) systems. The associ-ation constant, limiting molar conductance and distance parameter in H_2O-C_2H_5OH-MX (NaCl,KCl,CsCl,KBr) systems are regressed from Lee-Wheaton model. The re-sults show the orders of association ability of ions are Na~+>K~+>Cs~+ and Cl~->Br~-,and these four salts form ion-pair separated by solvent in ethanol. The improvedPitzer-Li equation is applied to calculate the short-range term of activity coefficient.The association of ions is taken into account and the results show that the procedureof our calculation is reasonable. When the concentration of salt increases,the activityof water decreases, but the activity of C_2H_5OH increases. It means that these saltspresent a salting-in effect for water but salting-out effect for C_2H_5OH.