CALORIMETRIC INVESTIGATION OF COMPLEX-FORMATION IN THE AQUEOUS FE(III)-CITRATE SYSTEM

We have made calorimetric measurements of thermal effects associated w ith adding NaOH(aq) or HCl(aq) to aqueous solutions (pH = 1.623) of fe rric chloride + sodium citrate. Combination of these measured heats wi th concentrations of various species calculated from stoichiometric co mpositions and previously known K and DELTAH values leads to DELTAH va lues for four aqueous Fe(III)-citrate complexes. Further combination o f DELTAG0 values from equilibrium constants with our DELTAH values lea ds to DELTAS0 values, which are discussed in relation to conventional ideas about relationships between entropy and solute-water interaction s.