CALCULATION METHOD OF REAL ACTIVITY COEFFICIENTS OF IONS BY EXAMPLE OF HYDROGEN AND CHLORINE IONS IN AQUEOUS HCl SOLUTIONS

Abstract

In this paper, we proposed a calculating method of the real individual activity coefficients. To calculate the energy of the ion, transfer through the interface we offered to use the value of the electrolyte solution surface potential, and to use electronegativity elements values for accounting contribution of the charge transfer energy between the surface and the bulk solution. To verify the proposed equation, the activity coefficients of hydrogen and chlorine ions in an aqueous HCl solutions were calculated over a wide range of electrolyte concentrations. The Debye-Hückel equation within 2nd approximation describes satisfactorily the dependence of the activity coefficient on the electrolyte concentration for anions, but not reproduce the minimum on the curve for cations. This dependence for the cation H⁺ is most extremal, and namely it is the reason of the choice of HCl for the model calculation. The calculated values were compared with the data obtained from the results of determining the activity coefficients by experimental method of "vertical jet" [1]. The comparison showed that our proposed equation reproduces the character of the concentration dependence of real activity coefficients not for anion only but for cation as well. Previously we found, that at low concentrations of solutes up to 0.1 mol/kg the values of some thermodynamic characteristics are strongly determined by not the volume concentration of the electrolyte, but the restructuring of the solvent structure in the surface layer of the solution, and therefore, the changing the energy state of the molecules at the interphase surface. Hence, the number of cations and anions at the surface in the areas of high and low bulk concentrations of electrolyte also differ greatly. Obviously, the small variation between calculated and experimental values of the real activity coefficients may be connected with necessity of using at calculation the bulk and surface concentration of ions. For citation:Fedorovа A.A., Sharonov N.Yu., Filippov D.V. Calculation method of real activity coefficients of ions by example of hydrogen and chlorine ions in aqueous HCl solutions. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2017. V. 60. N 3. P. 29-35.