Composition and Stability of Iron and Copper Citrate Complexes in Aqueous Solution

Abstract

The acidity constants of citric acid and the stability constants of the citrate complexes of copper(II), iron(II), and iron(III) have been measured at 25 °C in 0.1 M KNO 3 background. The measurements were based on mass balances on hydrogen ions, supplemented in the case of Cu(II) and Fe(III) complexes by measurements of free metal concentration with a solid-state copper-ion-sensitive electrode and a redox electrode respectively. The data required the assumption of a binuclear copper complex, but all complexes characterized were of 1:1 stoichiometry.