Thermodynamics of amalgam cells [M-Amalgam|MCl2 (m)|AgCl|Ag] (M = Sr, Ba) and primary medium effects in (methanol+water) and (ethanol+water) solvent mixtures

For the amalgam cell {MxHg1 - x|MCl2 (m)|AgCl |Ag} (with M = Sr, Ba) the potential difference E has been measured as a function of the mole fraction xM of the metal M in amalgams and of the molality m of MCl2 in {methanol + water} and {ethanol + water} solvent mixtures Z = {A + W} with mass fractions of alcohol wA ≤ 0.50 of alcohol, at temperature 298.15 K. The respective molal-scale standard potential differences Em° have been determined together with the relevant activity coefficients γ± as functions of the MCl2 molality. The Em° dependence on the alcohol mole fraction in the solvent mixture within the ranges explored turns out to be linear for both of these two metals M in the amalgams studied. Of course, also the molal-scale standard Gibbs free energy change (ΔG W→Z°)m=2F(WEm°- ZEm°), which constitutes the "primary medium effect" upon transferring MCl2 from pure water to the (alcohol + water) mixture, is linear in xA. In the same context, following Feakins and French's treatment, which implies volume fraction statistics, the relevant primary medium effects upon MCl2 on the mol • dm -3 scale have been analysed in terms of the expected linear relation of (ΔGW→Z°)c=2F(WE c°-ZEc°) against the logarithm of water volume fraction, leading to primary hydration numbers for SrCl2 and BaCl2, respectively, in acceptable agreement with Bockris' data based on different methods.