Thermodynamics of the amalgam cells {Cs-amalgam|CsX(m)|AgX|Ag} (X= Cl, Br, I) and primary medium effects in (methanol + water), (acetonitrile + water), and (1,4-dioxane + water) solvent mixtures.

The p.d. E of the amalgam cell {CsxHg1-x|CsX(m)|AgX|Ag} (X= Cl, Br, I) has been measured as a function of the mole fraction xCs of Cs metal in amalgams and of the molality m of CsX in (methanol + water), (acetonitrile + water), and (1,4-dioxane + water) solvent mixts. contg. up to 0.75 mass fraction of the org. component, at the temp. 298.15 K. The resp. std. molal potential differences Em Deg have been detd. together with the relevant activity coeffs. g+- as functions of the CsX molality. The found Em Deg values show a parabolic decrease with increasing proportion of the org. component in the solvent mixt. Anal. of the relevant primary medium effects upon CsX shows that the CsX transfer from the std. state in water to the std. state in the (aq. + org.) mixt. is always unfavored, and the acetonitrile is the least unfavored co-solvent studied. Anal. of the primary medium effect upon CsI in terms of Feakins and French's theory leads to a primary hydration no. close to zero, which is consistent with the results of supplementary EXAFS expts. on Cs+ and I- in (acetonitrile + water) solvent mixts.