物理化学学报 >> 1992, Vol. 8 >> Issue (02): 162-170.doi: 10.3866/PKU.WHXB19920205

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H2O-C2H5OH-MX(NaCl等)体系中离子缔合和活度

陆九芳; 胡贵春; 李以圭   

  1. 清华大学化学工程系，北京 100084
  • 收稿日期:1990-09-12 修回日期:1991-09-19 发布日期:1992-04-15
  • 通讯作者: 陆九芳

Ion Association and Activity in H2O-C2H5OH-MX(NaCl etc) Systems

Lu Jiu-Fang; Hu Gui-Chun; Li Yi-Gui   

  1. Department of Chemical Engineering, Tsinghua University, Beijing 100084
  • Received:1990-09-12 Revised:1991-09-19 Published:1992-04-15
  • Contact: Lu Jiu-Fang

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摘要： 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。

关键词: 离子缔合, 摩尔电导, 活度, 盐溶效应, 盐析效应

Abstract: 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 the activity 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 results 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 improved Pitzer-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 procedure of our calculation is reasonable. When the concentration of salt increases, the activity of water decreases, but the activity of C_2H_5OH increases. It means that these salts present a salting-in effect for water but salting-out effect for C_2H_5OH.

Key words: Ion association, Molar conductance, Activity, Salting-in effect, Salting-out effect