Thermodynamics of the amalgam cell: {MexHg1-x vertical bar MeCl(m)vertical bar AgCl vertical bar Ag} (with Me=K, Rb) in (methanol plus water) solvent mixtures

The electromotive force E of the amalgam cell {MexHg1-x\MeCl(m)\AgCl\Ag}, where Me = K or Rb, has been measured at the temperature 298.15 K as a function of the molality m of MeCl in (methanol + water) mixed solvents up to 0.8 mass fraction of methanol, with relative permittivities epsilon greater than or equal to 40, and as a function of the mole fraction x of Me in amalgam. The respective standard electromotive forces E-m(0) have been determined, together with the mean molal activity coefficients y(+/-) of the relevant MeCl as a function of its molality. For interpolation purposes the E-m(0) values can be expressed as a function of the methanol mass fraction w(M) by the following polynomials, valid for 0 less than or equal to w(M) less than or similar to 0.8: (for Me = K): E-m(0)/V = 2.19781 - 0.22826 w(M) + 0.17650 (w(M))(2) - 0.25229 (w(M))(3) (for Me = Rb): E-m(0)/V = 2.19221 - 0.24057 w(M) + 0.20271 (w(M))(2) - 0.23000 (w(M))(3) These results for standard e.m.f.s, interpreted in terms of primary medium effects, lead to primary hydration numbers n(hydr) = 6.6 for KCl, and = 6.7 for RbCl, in good agreement with previous results using different methods.