Solvation of ions,part XXX. Thermodynamics of transfer of copper ions from water to solvent mixtures

Free energies and Walden products show that the Cu⁺ and Ag⁺ ions are specifically solvated by acetonitrile (AN), 2-hydroxycyanoethane (HAN), and by pyridine (Py) whereas Na⁺ is specifically solvated by water, in mixtures of these organics with water. The Cu²⁺ ion is specifically solvated by pyridine in pyridine-water mixtures, but by water in acetonitrile-water mixtures. Ion-solvent, coordinated solvent-bulk solvent, and solvent-solvent interactions produce large entropy losses in the order Cu⁺Ag⁺>Na⁺ for transfer of these ions from water to dilute acetonitrile-water. The metallurgically important oxidations of copper, silver, CuS and Cu₂ with CuSO₄ in water are strongly favored in an enthalpic and free energy sense by the addition of acetonitrile, but addition of acetonitrile also produces a large loss of entropy for the reactions.