Influence of Ionic Traces Upon the Electric Conductivity of an Electrolyte Solution. On the Possibility of Obtaining the Trace Mobility of an Ion Exclusively by Conductance Measurements

Abstract

In a detailed theoretical and experimental study it is shown that the initial slope for the dependence of the conductivity of an electrolyte solution with respect to the concentration of an added trace electrolyte is not only determined by the trace ionic conductivity of the non‐common ion added plus the ionic conductivity of the common ion at the concentration of the original (supporting) electrolyte, as has been proposed by H. G. Hertz et al. (J. Chim. Phys. 78, 68 (1981)). It is also determined in a non‐negligible amount by the variation of the equivalent conductivity of the pure supporting electrolyte with concentration as well as by the variation of this conductivity with the composition of the mixture at constant total concentration. The theoretical equations are verified with the complete electric transport data of the system HCl‐KCl‐H2O and careful conductivity measurements for the system NaCl‐KCl‐H2O. It is concluded that the trace ionic conductivity of an ion in a mixture cannot in general be obtained by conductivity measurements alone (transport number determinations are unavoidable) and the proposal due to Hertz et al. is shown to be inadequate. Only in the case of H+ as a trace ion the later two dependences mentioned above can be neglected within an error of 1% at relatively low concentrations of the supporting electrolyte.