The redox reaction between the 12-tungstocobaltate(III) ion and carbohydrazide is first order with respect to both the oxidant and the substrate. The observed pseudo first-order rate constant, kobs, is retarded by increasing the concentrations of H+and alkali metal ion (Li+, Na+and K+). There is a linear correlation between the kobsand the concentrations of carbohydrazide and H+ion, but the plots of kobsagainst the concentrations of the alkali metal ions is non-linear. However, the same data is applicable to the Davies equation for the effect of the ionic strength on the kobs. Complex formation between the 12-tungstocobaltate(III) ion and carbohydrazide is indicated by optical density measurements, which increased with increasing H+concentration in the reaction mixture. This indicated that+H3NNHCONHNH2probably formed a complex with the 12-tungstocobaltate(III) ion. A suitable mechanism involving deprotonation of the complex and subsequent decomposition of the deprotonated complex as the rate limiting step is suggested. © 2008 Elsevier Ltd. All rights reserved.
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