A Method for Conductivity Measurements in Quantitative Analysis of Two-Component Solutions of Electrolytes

A method for computer processing of the results of conductometric measurements for a mixture of solutions of two electrolytes that differ in specific electrical conductivity is developed. This method makes it possible to determine the concentration of certain components taking into account the measurements of specific electrical conductivity and temperature. The method is based on approximations of theoretical dependences of electrical conductivity of electrolytes on concentrations according to the Robinson-Stokes and Kohlrausch equations and reference data on the dependence of electrical conductivity on temperature. In the region of concentrations of C 0.02 De and temperatures of 15-25A degrees D, the dependences are well approximated by algebraic polynomials up to the third order. The system of approximation functions describes a 3D region chi = f(C (1), C (2), T) inside of which there is a point that corresponds to the result of the measurements. This method is verified by the system of NaCl-NaOH and is applicable for the solutions of any concentrations by way of dilution of a sample to the required level. Two algorithms of processing of experimental data are studied. A simplified algorithm is based on the independence of molar electrical conductivity of the concentrations of the diluted solutions. The result of the processing of the experimental data has an overestimated systematic error from 1 to 5% in the mixtures with a high content of alkali. A more precise algorithm is based on the approximation of functions of dilution by the Kohlrausch equation. The systematic error of the specified algorithm is less than 0.05% in the mixtures with the highest electrical conductivity, and it is commensurable with the sensitivity of the conductometric measuring method.