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

The electromotive forces E of the amalgam cells {LixHe1-x \ LiCl (m) \ AgCl \ Ag} and {LixHg1-x \ LiBr (m) \ AgBr \ Ag} have been measured as a functi on of the mole fraction x of Li metal in amalgams and of the molalities m o f 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 + w ater) mixtures containing up to mass fi action 0.8 of the organic component , but only (acetonitrile + water) mixtures for LiBr. The standard molal ele ctromotive forces E-m(0) have been determined and, for all the solvent syst ems explored, they appear to vary linearly with the mole fraction gamma of the organic component involved, according to the following equations: E-m(0 )(LiCl)/V = 2.4169 - 0.2961 gamma(A); E-m(0)(LiCl)/V = 2.4175 - 0.5951 gamm a(D); E-m(0)(LiCl)/V =2.4163 - 0.1749 gamma(M); E-m(0)(LiBr)/V = 2.2672-0.2 092 gamma(A), where A denotes acetonitrile. D is 1.4-dioxane, and M is meth anol. The relevant mean molal activity coefficients as functions of the LiC l and LiBr molalities have also been determined. The primary medium effects upon LiCl and LiBr, analysed in terms of the Feakins-French theory, lead t o primary hydration numbers of approximate to 5 for LiCl and approximate to 4 for LiBr. These are somewhat lower than those obtained by other methods, but their difference is expected considering the known primary hydration n umbers of the anions Cl- and Br-. (C) 2000 Academic Press.