Kinetics and mechanism of oxidation of formic acid by bismuth(V) in aqueous phosphoric acid medium

The solution of bismuth(V) was prepared by digesting sodium bismuthate in aqueous phosphoric acid (3.0 mol dm(-3)), the resulting pink colour solution absorbs in the visible region at 530 nm (640 dm(3) mol(-1) cm(-1)). The stoichiometry of the oxidation of formic acid by bismuth(V) corresponds to the reaction as represented by the Eq. (1). Bi-V + HCO2H --> Bi-III + 2 H+ + CO2 The observed kinetic rate law is given by the Eq. (2) -d[Bi-V]/dt = (k(1) + k(2) K-a/[H+]) [Bi-V] [HCO2H] where Bi-V ande [HCO2H] are the gross analytical concentrations of bismuth(V) and formic acid respectively. A plausible reaction mechanism corresponding to the rate law (2) has been proposed. Also the pattern of reactivity of bismuth(V) in HCIO4-HF mixture and H3PO4 respectively has been compared. (C) 2000 John Wiley & Sons, Inc.