Kinetics and Mechanism of the Redox Reaction of Naphthol Green B with Hydrazine Dihydrochloride in Aqueous Acidic Medium

The kinetics of the redox reaction between naphthol green B and hydrazine dihydrochloride has been studied in aqueous hydrochloric acid medium at an ionic strength, I = 0.50 mol dm -3(NaCl), [H +] = 1.0×10 -4 moldm -3 (HCl) and T = 21±1°C. The redox reaction displayed a stoichiometry of 1:1 and obeys the rate law: -d[NGB 3-]/dt=k 2[NGB 3-][N 2H 4.2HCl]. Change in hydrogen ion concentration of the reaction medium has no effect on the rate of the reaction. Added cations and anions inhibited the rate of the reaction. The redox reaction showed negative salt effect, with the rate decreasing with increase in ionic strength of the reaction medium. Results of the Michaelis–Menten’s plot show that an intermediate complex was not formed during the course of the reaction. The outersphere mechanism is proposed for this reaction.