Conductance Measurements on Aqueous Solutions Over Extended Ranges of Concentration and Temperature

Abstract

A review is presented of models or transport and structure in liquids, with emphasis on aqueous solutions. Particular attention is paid to the temperature and composition-dependence of conductance, as these are the phenomena which have been studied in the present work. The conductivity and density of KCL and CaCl2 solutions have been measured over a wide range of composition and up to 350°C, at constant pressure. From these measurements the equivalent conductance can be calculated. In the low temperature region the equivalent conductance can be accounted for on the basis of theories which relate the conductance to the free volume or the configurational entropy in the solution. In the high temperature region the conductance passes through a maximum with increasing temperature, and is determined by both the thermal mobility of the ions and the number of free ions present. The temperature of the maximum equivalent conductance varies with composition in a way which has been related to the changing critical temperature. The isothermal composition dependence of conductance approaches the Onsager limiting law with increasing dilution, at all temperatures. However the data are well represented over a large range of composition by the predictions of a quasi-lattice or cell model. Partial molar volumes, and compressibilities, have been calculated from the density data. Hydration number derived from the compressibilities decrease with both increasing temperature and increasing salt concentration.