Thermodynamics of ions of chromic and thiocyanic acids: solvation in the ethanol–water system

Abstract

The standard electrode potential of Ag/Ag₂CrO₄ and Ag/AgSCN electrodes in the ethanol–water system (with 0, 10, 30, 50, 70 and 0, 10, 30, 50, 70, 90, 100 wt.% of ethanol, respectively) has been determined vs. an Ag/AgCl electrode in a liquid-junction cell in the temperature range 278.15–338.15 K. Solvation thermodynamic functions of stoichiometric mixtures of (2H⁺, CrO₄^2–) and (H⁺, SCN^–) ions have been calculated on the basis of the temperature dependence of the emf. The Gibbs energy of solvation has been divided into ionic contributions using the reference electrolyte extrathermodynamic assumption. The addition of alcohol to water has been observed by Gibbs energy of transfer analysis to reduce the stability of the complexes formed between chromic acid ions and solvent molecules, but to improve this stability in the case of thiocyanic acid.