Comparative study of equilibrium characteristics of Cu|Cu(II), Cu(I), glycine system containing sulfate or perchlorate as a supporting electrolyte

Abstract

The distribution of species in Cu(II)-glycine solutions, containing sulfate or perchlorate as a supporting electrolyte, is considered. Substantial differences are observed at pH < 4.5, where the molar fraction of monoligand complex (associate) CuSO4 reaches up to 20 percent of the total Cu(II) concentration. Cu(I)-containing species are generated at the Cu|solution interface. These are Cu+ aqua-complexes (acid media) or mono- and bidentate Cu(I)-glycine complexes (alkaline media). The addition of sulfate reduces the content of Cu+ ions, but practically does not affect the distribution of Cu(I) complexes. The study of acid-base equilibria involving Cu+ ions shows that the thermodynamic probability of Cu2O formation remains low in both perchlorate and sulfate media. HSO4– ions formed in acid media should be treated as rather labile proton donors. This is quantitatively confirmed by experimental data, according to which the rate of hydrogen evolution increases correspondingly when perchlorate is replaced by sulfate in glycine solutions.