Gibbs energies, entropies and enthalpies of transfer for divalent cations to several solvents

Abstract

Gibbs energies of transfer for the divalent cations Cu²⁺, Zn²⁺, Cd²⁺, Ba²⁺ and Pb²⁺ from the reference solvent N,N-dimethylformamide have been derived from reversible polarographic half-wave potentials via the bis(biphenyl)chromium assumption. Entropies of transfer were calculated from temperature coefficients of the half-wave potentials employing the assumption of a negligible thermal diffusion potential. Enthalpies of transfer were calculated from the equation Δ_tH°=Δ_tG°+TΔ_tS°. Thermodynamic transfer properties for Cu²⁺, Zn²⁺, Cd²⁺, Ba²⁺ and Pb²⁺ for up to 23 solvents were obtained. The Gibbs energies of transfer and the enthalpies of transfer reflected the principle of hard and soft acids and bases; the entropies of transfer of the divalent cations dependent linearly on each other for all solvents. The solvent effects on the transfer properties are accounted for as first-sphere interactions between the cations and the solvent molecules and by interactions of these entities with the surrounding solvent matrices.