The formation of hydroxy and chloro complexes of iron(III) in chloride and perchlorate media

Abstract

The hydrolysis of iron(III) has been studied by spectrophotometric methods in KaClO₄, NaCl, and CaCl₂ solutions all of the same ionic strength 0.15M. The measured values of the hydrolysis constants, expressed in a form which allows for association of iron with the supporting medium, were 14.5 x 10^-4 in NaClO₄, 8.8 x 10^-4 in NaCl, and 10.9 x 10^-4 in CaCl₂. In addition, the extent of complex formation between iron(III) and chloride ions has been measured in perchlorate solutions of the same ionic strength 0.15M. Assuming that only chloro complexes were formed in these systems, the stability constant of FeCl²⁺ formation was found to be 4.0.     All the results obtained were sufficiently consistent with each other, within experimental error, that the inclusion of terms to account for iron-perchlorate association was unwarranted. However, if iron-perchlorate association was assumed to exist and the results were treated accordingly, the stability constant of the associated complex was estimated to be 1.8.