The kinetics of oxidation of Ethylenediammine-N,N,N,N-tetraacetatocobaltate(II) complex (〖[Co(II)EDTA]〗^(2-)) by silver-activated persulphate ion in aqueous nitric acid medium was studied at I = 0.5 mol dm-3(NaNO3)1/6/2017 11:57:00 AM, [H+] = 1 × 10-2 mol dm-3, [Ag+] = 1 × 10-2 mol dm-3, T = 299 ± 1 K and λmax = 520 nm. Stoichiometric study showed 2:1 (Reductant: Oxidant) mole ratio. The reaction exhibited first order with respect to [Co(II)EDTA2-] and [ ] and the rate constant, k_2(5.90 × 10-2 dm3mol-1s-1) was independent acid concentration, but varied linearly with catalyst concentration, [Ag+]. The overall rate law is represented as:
(d[Co(III)EDTA^-])/dt= 5.90 ×〖10〗^(-2) 〖[Ag〗^+][〖Co(II)EDTA〗^(2-) ][S_2 O_8^(2-)]
The reaction displayed zero salt effect suggesting an activated complex composed of either a neutral-Charged, neutral-neutral reactant species or ion-pair. The reaction was catalysed by addition of formate ion, HCOO- and the Michaelis-Mentens plot gave zero intercept indicating the absence of intermediate complex. Also the activation enthalpy (〖ΔH〗^⋕= +39.27 KJ mol-1) and entropy (〖ΔS〗^⋕= -136.73 J K-1 mol-1) were determined. The entropy of activation shows a more ordered activated complex relative to the reactants species. Evaluating the experimental data, an outer-sphere mechanistic pathway via ion pair activated complex is proposed for the reaction.
Keywords: Kinetics, Oxidation, Aminocarboxylactocobaltate(II), persulphate ion
Key words: Kinetics, Oxidation, Aminocarboxylactocobaltate(II), persulphate ion
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