Kinetic Approach to Reaction among Bromate, Bromide and Iron(II) Utilized for Potentiometric Flow Injection Analysis of Trace Bromate Based on its Redox Reaction with lron(lll)-lron(ll) Buffer

Hiroki Ohura, Toshihiko Imato, Sumio Yamasaki, Nobuhiko Ishibashi

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    Abstract

    A highly sensitive potentiometric flow injection analysis (FIA) for bromate has been previously proposed by utilizing the detection of a large transient potential change which appears during the reaction of bromate with a Fe(III)-Fe(II) potential buffer containing bromide. The transient potential has been estimated to be due to bromine as an intermediate of the reaction (1). In this paper, in order to confirm the estimated reaction pathway and rate of the reaction (1), the overall reaction rate among bromate, bromide and iron(II) in sulfuric acid solution and reaction rates of each steps (a), (b) and (c) were measured by stopped-flow spectrophotometry by following the bromine concentration. The absorbance change at 447 nm was used for the determination of bromine. The absorbance change on addition of bromate to the reagent solution of iron(H) and bromide, showed the formation and decay of bromine, which indicates the successive reactions involving bromine as an intermediate. The rate constants, kFl, kF2 and kR for reactions (a), (b) and (c), respectively, were determined separately by measuring the concentration change of bromine as function of time. As results, the rates of reactions (a), (b) and (c) were expressed by Eqs. (2), (3) and (4), respectively. The rate constants, kFl, kF2 and kn were found to be 3.18±0.23, 1.98± 0.20 and 4.09 ± 0.15 l/(mol.s), respectively, in 0.6 M sulfuric acid solution at 25 °C. The concentration change of bromine in the overall reaction among bromate, bromide and iron(II) is expressed by Eq. (5), integrating and rearranging Eqs. (2), (3) and (4). The bromine concentration-time relation observed in above mixed solution was in good agreement with that calculated from Eq. (5) by using kFli kF2 and kR obtained.

    Original languageEnglish
    Pages (from-to)797-803
    Number of pages7
    JournalNIPPON KAGAKU KAISHI
    Volume1992
    Issue number8
    DOIs
    Publication statusPublished - Jan 1 1992

    All Science Journal Classification (ASJC) codes

    • Chemistry(all)
    • Chemical Engineering(all)

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