Electrical conductivity of aqueous solutions of aluminum salts

Abstract

We present experimental measurements of the specific electrical conductivity (sigma) in aqueous solutions of aluminum salts at different temperatures, covering all salt concentrations from saturation to infinite dilution. The salts employed were AlCl(3), AlBr(3), AlI(3), and Al(NO(3))(3), which present a 1:3 relationship between the electrical charges of anion and cation. In addition, we have measured the density in all ranges of concentrations of the four aqueous electrolyte solutions at 298.15 K. The measured densities show an almost linear behavior with concentration, and we have fitted it to a second order polynomial with very high degree of approximation. The measurement of the specific conductivity at constant temperature reveals the existence of maxima in the conductivity vs concentration curves at molar concentrations around 1.5M for the three halide solutions studied, and at approximately 2M for the nitrate. We present a theoretical foundation for the existence of these maxima, based on the classical Debye-Hu ckel-Onsager hydrodynamic mean-field framework for electrical transport and its high concentration extensions, and also a brief consideration of ionic frictional coefficients using mode-coupling theory. We also found that the calculated values of the equivalent conductance vary in an approximately linear way with the square root of the concentration at concentrations as high as those where the maximum of sigma appears. Finally, and for completeness, we have measured the temperature dependence of the electrical conductivity at selected concentrations from 283 to 353 K, and performed a fit to an exponential equation of the Vogel-Fulcher-Tamman type. The values of the calculated temperatures of null mobility of the four salts are reported.