Kinetics of the bromate-iodide-ascorbic acid clock reaction: Different mechanism of the molybdenum and vanadium catalysis

György Bazsa, István Fábián

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The kinetics of the molybdenum(VI)- and vanadium(V)-catalysed bromate-iodide-ascorbic acid clock reaction has been studied by means of spectrophotometry and pH-metric measurements. Two different types of catalysis were detected in this clock reaction. It was shown that MoVI catalyses the component process bromate + iodide of the clock system, while VV catalyses the direct reaction between bromate and ascorbic acid. The rate equation r = k2[BrO3-][I-][H+] 2 + k′2[BrO3-] [I-][H+]2[MoVI] describes the kinetics of the Mo-catalysed system, where k2 = 44 ± 2 dm9 mol-3 s-1 and k′2 = (4.3 ± 1) × 106 dm12 mol-4 s-1. In the vanadium-catalysed clock reaction the equation r = k′1[BrO3-][VV] + k2[BrO3-][I-][H+] 2 was found, where k′1 = 9.6 ± 1 dm3 mol-1 s-1 and k2 = 42.6 ± 2 dm9 mol-3 s-1. At lower acidities (pH > 3) more complex kinetics appeared and further study was abandoned.

Original languageEnglish
Pages (from-to)2675-2680
Number of pages6
JournalJournal of the Chemical Society, Dalton Transactions
Issue number12
Publication statusPublished - Jan 1 1986


ASJC Scopus subject areas

  • Chemistry(all)

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