Thermodynamical Behaviour of 1-1 Strong Electrolytes In Water, Dimethyl Sulfoxide And Water- Dimethyl Sulfoxide Mixtures.

Abstract

The densities, viscosities and relative viscosities of solutions of several univalent electrolytes Lithium bromide (LiBr), Sodium bromide (NaBr), Potassium bromide (KBr), Rubidium bromide (RbBr) Cesium bromide (CsBr) and reference salts tetra butyl ammonium tetra phenyl borate (BU4NBPh4 ), tetra butyl ammonium bromide (BU4NBr) and potassium chloride (KCl) were measured over the entire range of concentration at 25 oC to 45oC in pure DMSO, pure water and DMSO- H2O binary mixtures. Data was analysed by Jones-Dole equation to determine ion –ion interactions (the A- coefficients), ion- solvent interaction, (the B- coefficients) for alkali metal bromides in pure DMSO, pure water and DMSO- H2O binary mixtures. The values of A- coefficients were small and almost positive in all the cases. The values of B- coefficients were large and almost positive of all the salts in DMSO and DMSO- H2O mixtures, which showed the structure making abilities of the salts in DMSO- H2O mixtures at all the five temperatures. The values of viscosity B- coefficients were found negative for KBr, RbBr and CsBr in pure water at all the five temperatures, which showed the structure breaking abilities of the salts while the values of viscosity B- coefficients of LiBr and NaBr in water at all the five temperatures were found positive and behave as structure makers. iv The viscosity B- coefficient data was further splitted into ionic B- coefficient for non-aqueous solvents by using Gill and Sharma’s convention and Gurney’s convention into ionic B- coefficients for aqueous solvent systems. From ionic B- coefficient data it was observed that in pure DMSO all the alkali metals have strong structure making abilities. It was also observed that these structure making abilities were decreased with the increase in ionic radii or temperature. While in aqueous solvents (DMSO- H2O) mixtures the structure forming capabilities were weakened and structure breaking abilities were appeared at all temperatures. In pure water except Li+ and Na+ all the ions showed the structure breaking properties, which increased with the increase in temperature. The data obtained during this study was found in good agreement with those values which were already available in literature. The Transition state parameters such as free energies and energies of activation for viscous flow have been calculated for the whole solvent system. From the present study it is concluded that the energy of activation of viscous flow is influenced by the concentration and the size of the solute particles. So the energy of activation of viscous flow for CsBr is greater than for RbBr, KBr, NaBr and LiBr in DMSO and DMSO-H2O mixtures. It is also observed that the energy of activation of viscous flow are greater for alkali metal bromides in water than in DMSO due to the presence of a network of hydrogen bonds in water. For the free energy of activation for viscous flow, it is observed that the free energy of activation for viscous flow increases with temperature.