Kinetics of oxidation-reduction reactions between elements of Groups V and VII. Part I. Bismuth(V) with halide ions and other reductants

Abstract

The oxidations of the ions I^–, Br^–, Cl^–, SCN^–, Tl⁺. and IrCl₆^3– by bismuth(V) in perchloric acid solution all obey the rate expression –d[Bi^V]/dt=k[Bi^V], where k= 161·4 ± 8·0 s^–1 at [H⁺]= 0·5M, I= 2·0M, and t= 25 °C. Rates of reaction are practically independent of [H⁺] in the range 0·5–2·0M. Measurements at four different temperatures give E_a= 7·1 ± 0·3 kJ mol^–1 and ΔS^‡=–187 ± 1 J K^–1 mol^–1. Mechanisms consistent with this data are discussed and that involving (i) as the rate-determining step is preferred. [graphic omitted] → [graphic omitted] + 2H⁺(i) Potentiometric titrations give E⁰= 2·03 ± 0·17 V for the half-cell reaction Bi^V+ 2e → Bi^III at [H⁺]= 0·5M, I= 2·0M, and t= 25 °C.