INFLUENCE OF TEMPERATURE AND CONCENTRATION ON THE HYDRATION OF A STRONG ELECTROLYTE IONS
The regularities of diffusion processes and viscosity of strong electrolyte aqueous solutions such as potassium iodide, ions of which are characterized by negative hydration, and lithium sulfate, ions of which are positively hydrated, have been investigated. The manifestation of the effect of hydration in the solutions under study was experimentally revealed; it was found that the ion hydration process has a direct effect on the values characterizing the viscosity of the electrolyte solutions. The molar ratio was chosen as the independent variable for the concentration scale, that is associated with the fact that the volume dependence of viscosity is usually used for concentration (Einstein's formula). However, since the structure of the solution changes during dissolution, in practice the volume ratios are not determined, as a result, the molar ratio is quite close to the volume ratio. It was shown that for potassium iodide solutions in the concentration range of 0.025-0.035 mol/mol the hydration sign change from the negative to the positive value is observed at low temperatures. At higher concentrations, this dependence is adequately approximated by a straight line, which made it possible to estimate the activation energy value of the process (Ea ~ 20 kJ), which turned out to be higher than the activation energy of pure water. In the case of lithium sulfate aqueous solutions, no the hydration sign change effect was revealed. Experimental data were used to calculate the activation energy for lithium sulfate aqueous solutions (Ea ~ 14 kJ), which, on the contrary, turned out to be lower than the activation energy of pure water (Ea ~ 17.0 kJ). In addition, it was experimentally shown that the relative viscosity of aqueous solutions is inversely proportional to the relative diffusion of water molecules, both for lithium sulfate solutions and for potassium iodide solutions.