No abstract

The reduction potential for the hexacyanoferrate(III)-(II) couple has been measured potentiometrically over a range of temperature, pH, ionic strength, and in the presence of various 1:1 salts. The following thermodynamic quantities were obtained at 25.0°a nd I = 0: E°= 0.355 ± 0.001 v, AH°= -26.7 ± 0.3 kcal/mole, and AS°= -62.1 ± 1.0 eu. The data on the variation of reduction potential with concentration are shown to be consistent with the assumption of cation binding to both oxidant and reductant anions (thermodynamic parameters for these ion association equilibria are presented in part I). The strong salting-out effect of tetraalkylammonium salts on the reduction potential suggests that these ions exert an additional specific salt effect. The data on the variation of reduction potential with pH in solutions of pH <6 are shown to be consistent with the assumption that the reductant anion forms two successive conjugate acids. Potentiometric and calorimetric measurements lead to thermodynamic parameters for the protonation equilibria. Oxidation-reduction data for a number of complex ions are compared, and some factors which influence reduction potentials and entropies in these systems are discussed.

Thermodynamic data have been obtained for the acid ionization in dilute aqueous solution of the imino =NH group in imidazole and in its complex with sperm-whale ferrimyoglobin. For the ionization in free imidazole at 25",

No abstract

No abstract