FERRIC SULPHATE COMPLEXES, AND TERNARY COMPLEXES WITH THIOCYANATE IONS

Abstract

A spectrophotometric study of solutions containing ferric and sulphate ions, and also ferric, sulphate, and thiocyanate ions, is reported. The measurements were made at constant temperature and ionic strength; the effect of varying acidity was also investigated. The data were interpreted with the help of the results of the first paper of this series. It is believed that the data show that FeSO4+ and FeHSO4++ ions are formed. Values are obtained for the equilibrium constants for their formation from simple ions, and for their extinction coefficients. At higher sulphate concentrations there is evidence for the appearance of Fe(SO4)2− and FeSO4•HSO4, and estimates are made of their equilibrium constants. When thiocyanate is also present, the data can best be interpreted by assuming that the complex FeSO4•SCN is formed, and at higher sulphate probably also Fe(SO4)2SCN−−. Values are obtained for the equilibrium constants for the formation of these species, and the results would indicate that mixed complexes of this type are formed as readily as 'simple' ones such as Fe(SO4)2−.