Calorimetric investigation of complex formation in the aqueous Fe (III)–citrate system

Abstract

We have made calorimetric measurements of thermal effects associated with adding NaOH(aq) or HCl(aq) to aqueous solutions (pH = 1.623) of ferric chloride + sodium citrate. Combination of these measured heats with concentrations of various species calculated from stoichiometric compositions and previously known K and ΔH values leads to ΔH values for four aqueous Fe(III)–citrate complexes. Further combination of ΔG0 values from equilibrium constants with our ΔH values leads to ΔS0 values, which are discussed in relation to conventional ideas about relationships between entropy and solute–water interactions.