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Chemical acoustic emission analysis of the Briggs-Rauscher iodine clock Brock, Ivan Heinz


The oscillations observed in the Briggs-Rauscher Iodine Clock were studied using chemical acoustic emission (CAE) analysis. The experimental system evolved through three separate designs. The first early design employed a batch delivery system and utilized a piezoelectric transducer as the CAE sensor. The second design employed a flow delivery system and the oscillating reaction was monitored simultaneously by CAE, ultraviolet-visible spectrophotometry, and an ion-selective electrode. Sampling periods of 4.0 seconds made this a “low resolution” system. The third design was an optimized version of the second, with shorter sampling periods (1.0 seconds), which led to higher resolution data. The concentrations of the reagents used in the first system were those recommended by Briggs and Rauscher. Four unique phases of the oscillator were observed. The peak slopes during the positive slope phase increased according to second order kinetics, and the decreasing peak slopes during the negative slope phase were found to be independent of reagent concentration. Analysis of the averaged power spectra revealed two distinct frequency regions. Chemometric analysis successfully identified signals due to noise. A series of experiments were conducted in which [iodate] varied over a range of ca. 0.004 to 0.037 M at three different temperatures: 25, 30 and 35°C. It was discovered that the number of oscillations (both CAE and iodine oscillations) was independent of temperature. The CAB peak rates (increase and decrease) were also found to be independent of temperature while the iodine production and consumption rates were found to ca. triple with each five degree rise in temperature. Integrated CAE d.c. rates followed second order kinetics. Another series of experiments were conducted in which H₂O₂ was varied over the range of ca. 0.078 to 0.78 M at 35°C, The number of observed CAE oscillations was found to be independent of initial [H₂O₂] while the number of iodine oscillations increased as initial [H₂O₂] increased. Integrated CAE d.c. rates followed no simple trend. Under the conditions examined, a minimum [iodate] of 0.0 19 M, and [H₂O₂] of 0.16 M was required for oscillations to commence. Periodicity in the CAE data was noted in those experiments which did not strongly oscillate and attributed to a dissolved oxygen model. A refinement of the currently accepted mechanism is proposed and the utility of CAE as a tool to investigate oscillatory kinetics is discussed.

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