Thermodynamic determination of solvation potentials of divalent metal chlorides (MCl 2) in iso–dielectric media by EMF measurements

Abstract

Cell potentials (EMF) of metal chlorides (CoCl 2 and CuCl 2) were measured at T = (303.15 and 313.15) K on the cell: M X Hg|MCl 2 ( m) in solvent S|AgCl–Ag, where S = water or iso–dielectric media with water of FD + DMF or FD + D. Stock solutions of metal chlorides were prepared by mass in water/iso–dielectric solvents. There was a change in the EMF values in these iso–dielectric media from its pure components. This change of EMF was associated with the change of ion–solvent interactions and was explained on the basis of kinetics of electrode processes. Equilibrium constants ( K 1 and K 2) as well as the degrees of dissociation ( α 1 and α 2) values for two step dissociation of metal chlorides in these solvents were obtained by iterative procedures. The standard electrode potential ( E°) values of the above cell were calculated in these solvents, and same were used to get the mean ionic activity coefficients ( γ ±) and standard thermodynamic functions (Δ G°, Δ H°, and Δ S°) of MCl 2. The E° values were also used to compute the standard molar Gibbs free energy of transfer ( Δ G tr ∘ ) and other transfer thermodynamic parameters ( Δ H tr ∘ and Δ S tr ∘ ) of MCl 2 from water to iso–dielectric media.