SPECTROPHOTOMETRIC INVESTIGATION OF REDOX REACTION BETWEEN NAPHTHOL GREEN B AND THIOSULPHATE ION IN AQUEOUS ACID: KINETICS AND MECHANISTIC APPROACH METHOD

Abstract

The kinetics of the redox reaction of naphthol green B (here and thereafter referred to as (NGB3-) with thiosulphate ion has been studied using spectrophotometer at constant ionic strength, I = 0.50 C2mol dm-3 (NaCl), ?H+? = 1.0 ? 10-4 mol dm-3 (HCl) and T = 21 ?1?C. The redox reaction showed a stoichiometry of 2:1 and rate equation for the reaction is: -d[NGB3-]/dt = (a + b[H+])[NGB3-][S2O32-]. The rate of reaction slightly increased with increase in [H+] in the range of (0.5 – 9.0) × 10?4 mol dm?3 investigated. Changes in the ionic strength of the reaction did not affect the rate of the reaction. This showed zero BrØnsted - Debye salt effect. The reaction shows a first order dependence on [oxidant] and [reductant]. Added anion on the reaction rate does not have effect on the rate of the reaction. Michaelis – Menten’s plot of 1/k1 versus 1/ S2O32- and spectrophotometric test suggest presence of an intermediate in the rate determining step. There was evidence of gel formation by the addition of acrylamide to reaction mixture followed by excess methanol. The results obtained suggest the presence of the formation of intermediate complex. Therefore, innersphere mechanism is proposed for this reaction.