THE HEAT AND ENTROPY OF ASSOCIATION OF THE COMPLEX IONS FORMED BY EDTA WITH THE LANTHANIDE ELEMENTS IN AQUEOUS SOLUTION

Abstract

A radio tracer method has been used to measure the heat and entropy of association of all the lanthanide ions (except promethium) with the chelating agent EDTA. Entropy terms are largely responsible for the remarkable stability of these complex ions. The results suggest, but do not prove, that a change in configuration of the complex occurs after gadolinium (element 64).