Solvation of ions. Some applications. III. Solutions of copper(I) salts in water containing ligands

Abstract

Solutions of copper(II) and copper(I) sulphate in water containing acetonitrile have applications in the hydrometallurgy of copper. The potentials (n.h.e.) of the Cu⁺/Cu; the Pt/Cu²⁺, Cu⁺, and the Cu²⁺/Cu electrodes in water containing a large molar excess of various copper(I) bases and various counter-anions have been measured. Free energies of transfer of copper(I) ions from water to water containing the bases are calculated. ΔG_tr(Cu⁺) at 25°C becomes less exoenergetic for water containing the bases in the following order: CN^- >> S₂O₃^2- > Me₂NCHS > KI > NH₃ > C₅H₅N > KBr > KCl > C₃H₅OH ≥ MeCN, CO, C₂H₄ > C₃H₆. The reduction potentials of CuSO₄/Cu₂SO₄ in acidic saturated copper(II) sulphate solutions and a range of Cu₂SO₄ concentrations in acetonitrile- water mixtures show that CuSO₄/MeCN/H₂O is a powerful oxidant, comparable in strength to acidic iron(III) sulphate in water. Acetonitrile is the preferred base for the processing of copper by way of solutions of copper(I) sulphate.