Density, Viscosity, and Electrical Conductivity Measurements on the Ternary System H₂O + C₂H₅OH + LiCl over the Entire Ranges of Solvent Composition and LiCl Solubility from (−5 to +50) °C

Abstract

Systematic measurements of density, viscosity, and electrical conductivity on the ternary system water + ethanol + lithium chloride over entire ranges of solvent composition and LiCl solubility from (−5 to +50) °C have been carried out. The temperature-independent aquamolality scale, m (LiCl moles per 55.5 moles of solvent) has been used to justify data comparison not only at different temperatures but also for the solutions in various solvent mixtures. Density isotherms (fitted to second-order polynomials in m ) provided a composition-dependent density index, g(x 1), which can conveniently be used to determine the density at any desired LiCl concentration, mixture composition, and temperature. Excess molar volumes (V E) of the solvent mixtures have been calculated over the whole temperature range, and minima of all the V E isotherms at the same water mole fraction, x 1 = 0.6, suggest that no significant structural rearrangement takes place in the solvent mixtures upon temperature variation. From the density data, the “temperature average coefficient of thermal expansion” (β) is also determined for all the samples. Fitting the viscosity (η) isotherms to an extended Jones-Dole-type cubic equation in m provided coefficients related to various interactions taking place in the solutions. The temperature dependence of the entire η data can well be explained by the Arrhenius-type equation involving single flow activation energies (E a) that always increased with LiCl concentration for a given solvent but exhibited a sharper rise for the ethanol-rich mixtures; E a values tend to pass through maxima at x 1 ≈ 0.6. In all the cases, electrical conductivity (κ) plotted against m exhibits maxima which shift from 4.5 m to ∼6 m in the water-rich mixtures, and exhibition of the κ-maxima has been explained with a simple model according to which κ at any given m is comprised of two sets of the oppositely acting terms, namely κup and κdown. Since all the κ plots fit very well to third-order polynomials in m with negligibly small coefficients of the cubic terms, the other two terms involving m and m 2 can be compared with κup and κdown, respectively. From temperature variation of molar conductivity, activation energies have been determined and compared with those of viscous flow.

Density and Excess Molar Volumes of 1-Butanol + Methanol + Electrolyte Systems in the Temperature Range 293.15–308.15 K

“…Values of d 1 and d 2 in their respective appropriate units fall in the ranges +0.028 to +0.034 and −0.010 to +0.014, respectively; d 1 -values for the system under consideration may be compared with the gradient (dρ mix /d x 1 ). It ( d 1 ) being a useful structural parameter, has shown linear relation with temperature ( R 2 = 0.9993) for the aqueous ethanol suggesting that no significant structural change in the solvent mixture has taken place with temperature. However, the mixture under consideration does not show such behavior.…”

“…However, the mixture under consideration does not show such behavior. On the other hand mixture densities at various compositions tend to decrease linearly ( R 2 ≈ 1) with temperature and the slope values range between −9.4·10 –4 and −7.6·10 –4 g·cm –3· K –1 from lower to higher x 1 ; the slope (dρ mix /d T ) = α is a quantity related to the thermal expansion coefficient. , The density variation of a given mixture with external parameters could possibly be connected to the volume change via modification of specific intermolecular interactions. This may better be substantiated by investigating thermodynamic properties like molar ( V m ) and excess molar ( V E ) volumes; V m = (M mix /ρ mix ) is calculated from the measured density ρ mix .…”

“…The measured ρ values are listed in Table through Table and are plotted in Figure and Figure . The concentration gradient, dρ/d m ≡ (g/g·cm –3· molal –1 ) is yet another important parameter for the given electrolyte-solvent system . The gradient value can be considered as an indicator for structural changes that occur in the system on the electrolyte addition.…”

“…The solution density (ρ) shows slightly nonlinear variation with CdI 2 concentrations over the entire mixture range at various temperatures; the plots were fit to a quadratic term in x 1 showing negligible contribution of the third term (parameters given in Figures ). This allows the generalized linear equation where ρ o,mix is the graphically determined mixture density and g is the gradient mentioned above. Values of ρ o,mix are in good agreement with the measured densities, ρ mix (Table ); values of ρ o,mix and g are listed in Table .…”

“…Densities were measured at the selected temperatures using a DMA 4500 Anton Paar (Austria) vibrating tube density meter having a resolution of 5·10 –5 g·cm –3 . The instrument is equipped with an automatic temperature controlling sensor having uncertainty within ±0.01 °C and has provision of preadjusting for both air and water samples as references but the calibration was also done using a toluene (GC-grade from Merck, purity ≥99.9%) sample as described earlier …”