Kinetics of Cu2+– Catalysed Redox Reaction of n-(2-hydroxylethyl) ethylenediaminetriacetatocobalt(III) with Hydrazine Monohydrate in Aqueous Acid

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A. D. Onu

Abstract

Communication in Physical Sciences 2018, 3(1): 10-17


Received 24 November 2017/Accepted 23 July 2018


Authors: A. D. Onu, S. O. Idris & B. Y. Abiti


The kinetics of the Cu2+-catalysed redox reaction between n-(2-hydroxylethyl) ethylenediaminetriacetatocobalt(III) (hereafter [Co(HEDTA)OH2]) with hydrazine monohydrate (hereafter N2H5+) have been successfully investigated in aqueous acidic medium, under the following conditions T = 298 ± 1 K, I = 0.5 mol dm3 (NaClO4), [H+] = 4.0 × 10-3 mol dm-3 (HClO4), [Cu2+] = 5.0 × 10-4 mol dm-3 and λmax = 550 nm. Stoichiometric study revealed that two moles of [Co(HEDTA)OH2] reacted with one mole of N2H5+.The rate of the reaction was first order with respect to [Co(HEDTA)OH2] and [N2H5+], and second order overall, with k2 = (9.81 ± 0.14) × 10-2dm3 mols-1. The rate of the reaction was inversely dependent on [H+] but directly proportional to [Cu2+] and both plots of k2 versus [H+]-1 and k2 versus [Cu2+] were linear from the origin, indicating a one term rate law with respect to both [H+]-1 and [Cu2+]. Changes in ionic strength had no effect on the reaction rate and temperature dependent study gave values of activated enthalpy (ΔH‡) and entropy (ΔS) as 82.89 KJ mol-1 and 17.13JK-1 mol-1respectively. Spectroscopic and kinetic investigations indicated absence of detectable intermediate. Analysis of evidence adduced from the study favour the outer-sphere mechanism and it is proposed for the reaction.

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A. D. Onu, Federal College of Education, Zaria, Nigeria

Department of Chemistry