Thermodynamics of the cell { Li- Amalgam | LiX (m)| AgX | Ag }(X = Cl,Br) and medium effects upon LiX in (acetonitrile + water), (1,4-dioxane + water), and (methanol + water) solvent mixtures with related solvation parameters

Abstract

The electromotive forces E of the amalgam cells {LixHg1−x| LiCl(m)| AgCl | Ag} and {LixHg1−x| LiBr(m)| AgBr | Ag} have been measured as a function of the mole fraction x of Li metal in amalgams and of the molalities m of LiCl as well as LiBr at T= 298.15 K. For LiCl, the solvents investigated have been (acetonitrile + water), (1,4-dioxane + water), and (methanol + water) mixtures containing up to mass fraction 0.8 of the organic component, but only (acetonitrile + water) mixtures for LiBr. The standard molal electromotive forces Emohave been determined and, for all the solvent systems explored, they appear to vary linearly with the mole fraction y of the organic component involved, according to the following equations: Emo(LiCl)/V = 2.4169 − 0.2961yA;Emo(LiCl)/V = 2.4175 − 0.5951yD;Emo(LiCl)/V = 2.4163 − 0.1749yM;Emo(LiBr)/V = 2.2672 − 0.2092yA, where A denotes acetonitrile, D is 1,4-dioxane, and M is methanol. The relevant mean molal activity coefficients as functions of the LiCl and LiBr molalities have also been determined. The primary medium effects upon LiCl and LiBr, analysed in terms of the Feakins–French theory, lead to primary hydration numbers of ≈5 for LiCl and ≈4 for LiBr. These are somewhat lower than those obtained by other methods, but their difference is expected considering the known primary hydration numbers of the anions Cl−and Br−.