African Journal of Chemistry

African Journal of Chemistry ISSN 4391-3199 Vol. 6 (1), pp. 398-403, January, 2019. © International Scholars Journals

Full Length Research Paper 

Kinetic approach to the mechanism of the redox reaction of malachite green and permanganate ion in aqueous acidic medium

Y. Mohammed1*, J. F. Iyun2 and S. O. Idris2

1Chemistry Department, Nasarawa State University, P. M. B. 1022, Keffi. Nigeria.

2Chemistry Department, Ahmadu Bello University, Zaria, Nigeria.

Accepted 9 November, 2018

Abstract

The redox kinetic and mechanistic studies of the reactions of malachite green (MG+) and MnO4 were carried out in aqueous acidic medium, at a temperature of 32.5 ± 0.5°C; ionic strength, m = 0.50 mol dm–3 (Na2SO 4), [H+] = 5.00 x 10–3 mol dm–3 (H2SO4). In the stoichiometry, one mole of malachite green was consumed by one mole of MnO4. The reaction is first order in both [MG +] and the [MnO4]. The rates of redox reaction showed dependence on acid concentrations (in the acid range used). Rate equation for the reaction has been proposed as: –d[MG+]/ dt = (a + b[H+])[MG+][MnO4]. At [H+] = 5.00 x 10–3 mol dm 3, the second order rate constant for the malachite green – MnO4 reaction was found to be (11.96 ± 0.13) x 10–3 dm3 mol–1 s–1. The rates of reaction displayed negative salt effect. Log k1 versus 1/D gave positive slope for the reaction. Added anions and cations catalysed the malachite green – MnO4 reaction. Results of the Michaelis- Menten analysis gave no evidence of intermediate complex formation. Based on the results obtained experimentally, the outer sphere mechanism is proposed for the malachite green – MnO4 reaction.

Key words: kinetics, mechanism, catalysis, salt effect.