The potential response of silver halide membrane electrodes to the corrosive bromous, bromic, iodous, and iodic acids is investigated in sulfuric acid solutions ([HzS04] = 0.15 and 1.5 M), typical media for several well-known oscillating reactions. The syntheses of the materials (bromide-free NaBrOz and HIOJ needed for the experiments are described. The potentials recorded as a function of time were used for the determination or estimation of several rate constants at 24 f 1 "C: the disproportionation rate constant of HBr02 is kgl = (1.4 f 0.2) X lo3 M-' s-l (in 0.15 M HZSO,) and (3.8 f 1.0) x lo3 M-'s-l (in 1.5 M HZSO,); the corresponding value for HIOz is kIl < 5.4 M-' s-l (in 0.05-0.15 M H2S04); the disproportionation of HIO2 is autocatalytic, the rate-determining step is a reaction of HIOz with HzOI+, the rate constant of which is lzI, = 130 f 5 M-' (in 0.15 M HZSO,); the rate constants of the reactions of HBrOz with Br-and H+, and HIOz with I-and H+ are 106 < kg2 < 4 X 106 M-z s-l (in 1.5 M H2S04) and 106 < ItI, < 4 X lo7 M-z s-l ( i n 0.15 M H2S03, respectively.The corrosive reactions of the halous and halic acids with halide ions are much slower than those of hypohalous acids, which fact required the development of the theory for slow corrosive reactions. Criteria for the definitions of "slow" and "fast" corrosive reactions are given. The possibility of a second autocatalytic process in the halate driven oscillating reactions is demonstrated. On the basis of these results, a generalized Lotka-Volterra scheme is proposed for the BZ, BL, and BR oscillators.
IntroductionThe present paper is the second communication in a series devoted to studying the potential response of ionselective electrodes to corrosive species in oscillating chemical systems. The ultimate goal of our work is to provide a consistent interpretation of the potential changes displayed by bromide-and iodide-selective electrodes in the course of chemical oscillations, in terms of concentration changes of the several different intermediates involved. As a first step toward that goal, in a previous paper3 we have shown that halide-ion-sensitive electrodes, besides halide ions, also respond to hypohalous acids. Furthermore, we have demonstrated that in the latter case the electrode response can be best explained by the corrosion potential theory (CPT). The corrosion reaction
in D20 were recorded on a Varían T-60 spectrometer at 42.5 °C. The quaternary methyl peak was observed at 5 3.2 in all four samples, indicating no observable interaction between this group and hydroxide ion and no decomposition. The -methylene resonances, at about <5 3.4, were found to shift steadily upfield on addition of NaOH. By use of this shift, the percent of anhydrocholine formed was calculated and compared with that calculated from our aqueous AH and AS values (Table VI).Considering the very large concentrations that had to be used and the change from H20 to D20, the agreement is quite reasonable. This experiment was repeated in H20 solvent with similar results.Calorimetry. Heats of solution were measured with an LKB-8700 reaction and solution calorimeter.
Das Potential‐Verhalten von Ag‐halogenid‐Membran‐ Elektroden gegenüber den korrosiven Säuren HXO, und H + X0; (X: Br, I) wurde in 0.15 und 1.5 M H2SO4‐Lösungen als typischen Medien für oszillierende Reaktionen untersucht.
Das Potentialverhalten von ionenselektiven (AgCl‐, AgBr‐ und Agl‐Membran‐) Elektroden gegenüber Unterhalogenigen Säuren (HOCl, HOBr und H2OI+) wird unter experimentellen Bedingungen untersucht, wie sie bei oszillierenden Reaktionen vorherrschen, d. h. bei H,SO4‐Konzentrationen von 0.15 und 1.5 M (Unterhalogenige Säuren sind bekanntlich Zwischenprodukte in solchen Reaktionen).
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