keywords: Kinetics, malachite green, mechanism, outer-sphere, sulphite
Electron transfer reaction between malachite green and sulphite ion have been investigated in aqueous hydrochloric acid medium under pseudo-first order conditions at 27 ± 1°C, [H+] = 5.0 × 10-3 mol dm-3, I = 0.1 mol dm-3 (NaCl) and λmax = 620 nm. The reaction was first order in [MG+] and [SO ]. Effect of changes in hydrogen ion concentration on reaction rate is negligible and the reaction displayed a positive Bronsted-Debye salt effect. There was no evidence of intermediate complex formation and free radicals were absent. The observations suggest an outer-sphere mechanism for the reaction. The reaction obeys the rate law: -d[MG+]/dt = k2 [MG+][SO ]. A plausible mechanism has been proposed for the reaction.