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 ε≥40, and as a function of the mole fraction x of Me in amalgam. The respective standard electromotive forces E0m have been determined, together with the mean molal activity coefficients γ± of the relevant MeCl as a function of its molality. For interpolation purposes the E0m values can be expressed as a function of the methanol mass fraction wM by the following polynomials, valid for 0 ≤ wM≤0.8: (for Me = K): E0m/V = 2.19781-0.22826 wM + 0.17650 (wM)2-0.25229 (wM)3 (for Me = Rb): E0m/V = 2.19221-0.24057 wM + 0.20271 (wM)2-0.23000(wM)3 These results for standard e.m.f.s, interpreted in terms of primary medium effects, lead to primary hydration numbers nhydr = 6.6 for KCl, and = 6.7 for RbCl, in good agreement with previous results using different methods.