X-Ray Diffraction Study on Hydration and Ion-Pairing in Aqueous ZnSO4 Solution

Abstract

An X-ray diffraction experiment on a 2.98 molar ZnSO4 aqueous solution has been interpreted in terms of coordination models. The best agreement between model and experimental structure functions was reached when the Zn2+ ion is hydrated in octahedral form, with twelve water molecules in a second hydration shell, bonded by shortened H-bonds to the first hydration shell. The sulfate group is loosely coordinated by 8.2 water molecules. Besides the dominating Zn(H2O)2+ 6 complexes, about 40% [Zn(H2O)5SO4] inner complexes were found to be consistent with the X-ray data. Alternative models of cationic hydration are critically examined and for the sulfate group the independent atom approximation is compared with a spherical molecular description.