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 a queous 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 st oichiometry of the oxidation of formic acid by bismuth(V) corresponds to th e 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 p roposed. Also the pattern of reactivity of bismuth(V) in HCIO4-HF mixture a nd H3PO4 respectively has been compared. (C) 2000 John Wiley & Sons, Inc.