Reexamination of Gas Production in the Bray–Liebhafsky Reaction: What Happened to O₂ Pulses?

Abstract

Results of high-precision measurements of gas production in the BL reaction are presented, and an efficient kinetic model for their analysis is proposed. Based on this model, the data have been examined pulse by pulse, and for the first time, the entire records of gas production could be successfully reduced to series of just a few key parameters. It has been confirmed that the kinetics of O2(g) production is of the first order with respect to its precursor. Overall, only two steps have been found necessary to fit the observed pulses in gas production. The first step produces the precursor of the recorded O2(g), and its rate has two components. One component provides the peaks, and its approximation in the form of Gaussian functions has been found as satisfactory. The other component provides the constant baseline of gas production between the pulses. Finally, the precursor gives rise to O2(g) in the second step, and the simple first-order kinetics suggests that the precursor is otherwise relatively unreactive, making O2(aq) a logical candidate. However, the rate constant of this process showed almost perfect linearity with the actual concentrations of H2O2, and it was affected only little by variations in the rate of stirring. It thus seems possible that this final step in gas production, responsible for the majority of O2 produced in pulses, might not be the interphase transport O2(aq) → O2(g), as expected. Instead, it might be a truly chemical process, giving rise to O2(g) in a reaction of H2O2 with another precursor, which is not involved significantly in any other process, but it is not O2(aq). If this is true, the second-order rate constant of this process in the system with initial composition of 0.360 M KIO3, 0.345 M H2O2, and 0.055 M HClO4 at 60 °C would be 0.25-0.30 M(-1)·s(-1), depending on the rate of stirring.

Intermittent chaos in the Bray–Liebhafsky oscillator. Temperature dependence

“…Three of the channels were used to deliver the reactants (aqueous solutions of potassium iodate, sulphuric acid, and hydrogen peroxide) and one channel of the other pump was used to remove the surplus volume of the reaction mixture through a U-shaped glass tube, as in all our previous experiments where various dynamic states were analysed. 12,13,[33][34][35][36][37][38] For many years, we have succeeded with this technique to obtain reproducible results during the examination of BL systems, although it is known that there is an important influence of iodine and oxygen from gas phase on the reaction 37,39 and also that the regime of suction of the vapor or gas phase above the reaction solution may cause changes in the behavior of the reaction solution. 12 But if the suction of the liquid phase is used for a volume control in the steady state, as it was done in our case, then less perturbation of reaction in the liquid phase is obtained than in the case when overflow is used.…”

Platinum as a HOI/I2 Redox Electrode and Its Mixed Potential in the Oscillatory Briggs–Rauscher Reaction

“…• /H 2 O 2 in a BR reaction, 4 whereas others suggest that the I 2 /I − redox couple plays the role of the potential-determining redox pair in the BL system. 5 There were somewhat similar uncertainties regarding the potential of a AgI electrode. In particular, it was not clear how hypoiodous acid might affect the potential of a AgI or a Pt electrode.…”

“…Moreover, there is no general agreement concerning the potential-determining redox pair for a Pt electrode in the BR or in a BL reaction. Some authors assume that it is the HO 2 • /H 2 O 2 in a BR reaction, whereas others suggest that the I 2 /I – redox couple plays the role of the potential-determining redox pair in the BL system . There were somewhat similar uncertainties regarding the potential of a AgI electrode.…”

Problem and Solution of UV–Vis Time-Based Measurements of a Chemical System Involving Gas Product: Application to the Bray–Liebhafsky Oscillatory Reaction

“…It should be emphasized that the noise is larger in the oscillatory period compared to the induction period of the BL reaction. As expected, with the increase of the H 2 O 2 concentration, the amount of oxygen released also increases, and a larger amount of oxygen is produced in the BL oscillatory period than in the BL induction period. , Considering that the majority of O 2 is produced in pulses, it seems that the internal standard absorption vs time curve is a good presenter of oxygen dynamics. Subtracted curves are shown in blue in the given Figures –.…”