A TEMPERATURE-JUMP STUDY OF KINETICS OF FORMATION OF MONOSULFATO COMPLEX OF IRON(3)

The rate of formation of the monosulfato complex of iron(III) has been studied in acidic aqueous solution at 25° and ionic strength of 1.2 and 2.0 M and in the temperature range of 7-33° at ionic strength 0.5 M. Over the range of acidity studied at μ = 0.5 M (0.01 M ≤ [H+] ≤ 0.41 M), the complex formation occurs significantly via two paths: i.e., an acid-independent path and a second path dependent on the reciprocal of the hydrogen ion concentration. The investigations performed at ionic strength of 1.2 and 2.0 M over a wider acidity range have shown that an additional path dependent on [H+] also contributes to the complex formation at higher acidities. Activation parameters for the formation and dissociation of FeSO4+ lead one to consider Fe3+ and SO42-, rather than FeOH2+ and HSO4-, as the reactants in the acid-independent path. The results are in agreement with the view that the elimination of a water molecule coordinated to the metal ion is the rate-determining step in all cases, even though for the reaction of Fe3+ with SO42- the water elimination rate may be probably somewhat enhanced.