ION-SOLVENT INTERACTIONS OF ZINC(II) SALTS IN WATER-PYRIDINE MIXTURES

The ion-solvent interactions involving zinc(II) salts viz. iodate, fluoride and benzoate in water-pyridine mixtures have been investigated by solubility and solvent transport number measurements. The standard Gibbs transfer energies of the salts (DELTA-G(t)0), determined from their saturation solubilities in the solvent mixtures, decrease up to x(py) = 0.1 for zinc(II) iodate, but up to x(py) = 0.4 for zinc(II) benzoate, and subsequently increase with the addition of pyridine. For zinc(II) fluoride, however, a continuous increase of DELTA-G(t)0 with the addition of pyridine is observed. The transfer energy of Zn2+ is negative and that of anions is positive with the former decreasing and the latter increasing continuously with the addition of pyridine. The solvent transport number of pyridine (DELTA-py) is positive and passes through a maximum for all the salts in the range x(py) = 0.25 to 0.55. These results indicate a heteroselective solvation of the salts with Zn2+ being preferentially solvated by pyridine and the anions by water.