Oscillating chemical reaction metal catalyst

Numerous versions of the Belousov-Zhabotinsky system differ by chemical compounds used. The typical reaction involves oxidation of some organic compound by bromate ion (BrOj ) occurring in acid medium with metal catalyst (Ce3+, Mn2+, as well as complexes of Fe2+, Ru2+). As an example, a particular reaction [4] could be mentioned, where an organic reductor is malonic acid CH2(COOH)2 and Ce3+ ions serve as a catalyst. In this reaction a solution changes periodically its colour due to oscillations in Ce3+ concentration. Generally speaking, the reaction consists of two stages. At the first one metal is oxidized... 

The important techniques for measuring the oscillations in the chemical reaction are the potentiometry. The advantage of this technique is that by using a bromide ion-sensitive electrode, the composition of bromide ions in the reaction system can be monitored easily. However, platinum electrode is susceptible to changes in the oxidation state of the metal-ion catalyst. The measured electrode potential can be used to monitor oscillations in [Br ] and [Mox]/[Mjed] with the help of a suitable reference electrode. 

The BZ oscillating reaction has been discovered by B.P. Belousov, in 1951. In his early attempt, he wanted to make a chemical model for Krebs cycles (an energy pathway). For experimentation, he used KBr03, acidified solution of citric acid and a metal catalyst (Cerium (TV) metal ions). A redox indicator has also been used for observing the end of the reaction-phase. They found that the citric acid is oxidized into CO2, and B1O3 is reduced to Br ion. He observed a periodic color changes for duration of 10 min. He wanted to publish this report but editor refused his proposal and explanation because, it seems to be contrary with 2nd laws of thermodynamics. 

Diode array spectrophotometers can be especially useful because a complete spectrum can be collected in a short interval of time, making it possible to follow several species in a single experiment by taking repeated spectra. Also, several diode array instruments come with an open sample compartment, which makes it relatively easy to construct a flow reactor that can be placed in the light path of the instrument. The metal ion catalysts used in the BZ system absorb in the visible spectrum, so that UV/vis studies of the cerium-catalyzed or ferroin-catalyzed reaction are easy to perform. Iodine is another strongly absorbing species that is found in a number of chemical oscillators. Frequently, iodide ion is present as well, and the system is monitored at the iodine-triiodide isosbestic point at 471 nm. 

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