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Kinetics and mechanism of oxidation of pyrocatechol violet by iodate ion in aqueous hydrochloric acid

A.Adetoro*, J.F.Iyun, S.O.Idris

The kinetic and mechanismof the oxidation of pyrocatechol violet ( hereafter referred to as PCVH) by iodate ion (IO3 -) have been studied in aqueous hydrochloric acid at ionic strength = 0.5mol dm-3 (NaCl), [H+]= 5ï‚´10-5 mol dm-3 (HCl), T=27± 0.1ï‚°C. The reaction is first order in both [PCVH] and [IO3 -]. The redox reaction displayed a stoichiometry of 1:1 and obey the rate law: (a b[H ][PCVH][IO ] dt d[PCVH] 3     where a = 0.03 dm3mol-1s-1, b = 280.24 dm6mol-2s-1. The second order rate constant increaseswith increase in acid concentration and ionic strength respectively. This system displayed positive salt effect while spectroscopic investigation and Michaelis- Menten plot showed no evidence of intermediate complex formation.A plausible mechanism has been proposed for the reaction.