The kinetics of the oxidation of naphthol green B (NGB3？) by peroxydisulphate ion has been carried out in aqueous acidic medium at of 700？nm, °C, and ？mol？dm？3 (NaCl). The reaction shows a first-order dependence on oxidant and reductant concentration, respectively. The stoichiometry of the NGB— reaction is 1？:？2. Change in hydrogen ions concentration of the reaction medium has no effect on the rate of the reaction. Added cations and anions decreased the rate of the reaction. The results of spectroscopic and kinetic investigation indicate that no intermediate complex is probably formed in the course of this reaction. 1. Introduction Naphthol green B is used in histology to stain collagen. The dye is a lake, in which the mordant metal is ferric iron. However, the iron appears to play no part in its staining ability [1]. Naphthol green B is very soluble in water and has an absorption maximum of 714？nm. As an anion, it acts as an acid dye [2]. Kinetic spectrophotometric method for the determination of cerium (IV) with naphthol green B has been studied [3]. The reaction was monitored spectrophotometrically by measuring the decrease in absorbance of naphthol green B at 710？nm. It was found that the reaction rate is very slow when the temperature is below 60°C, but the rate of the catalyzed reaction increases rapidly when the reaction temperatures are above 70°C. Peroxydisulphate ion is one of the powerful oxidizing agents known [4, 5]. A large number of investigations have been carried out in the oxidation of metal ions [6, 7], metal complex [8, 9], and various organic compounds [10] by . Most electron transfer reactions of occur by the outer-sphere mechanism [11–13]. However, reactions with some positively charged metal complexes such as Fe , Fe , and Os occur by both the outer-sphere and the inner-sphere mechanisms [5, 9]. Except when the reducing agent can be protonated, the redox reaction of was found to be independent of hydrogen ion concentration [14]. Despite its reactions with other compounds, the redox reaction of this oxidant with naphthol green B is scanty. It is our hope that this investigation will help to gain more insight into the redox reaction of naphthol green B with peroxydisulphate ion. 2. Materials and Methods The chemicals used were of analytical grade and were used without further purification. Standard solution of was prepared by dissolving 0.088？g in 100？cm3 volumetric flask using distilled water. Sodium peroxydisulphate solution was prepared by dissolving known quantities in distilled water. All other reagents used were of analytical
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