Abstract
The kinetics of the electron transfer reaction between Bromopyrogallol (BPR2-) and nitrite ion in aqueous acidic solution has been studied in the acid range 0.1 × 10-4 ≤ [H+] ≤ 2 × 10-4 mol dm-3, ionic strength 0.01 ≤ ≤ 0.18 mol dm-3 (NaCl) and T = 29 ± 1.°C. The reaction shows a first order dependence on oxidant and reductant concentration respectively. The rate of the reaction increases with increase in [H+]. Plot of k2 versus [H+] was linear with a positive intercept. The overall reaction conforms to the rate law: -d[BPR2-]/dt = (a + b[H+])[BPR2][NO2-]. The stoichiometry of the reaction is 1:1 (BPR2- : NO2-). Added anions had no effect on the rate of the reaction. The results of spectroscopic investigation indicate that no intermediate complex is probably formed in the course of this reaction. The reaction is believed to proceed via the outersphere mechanistic pathway.
Highlights
Oxidation-reduction reaction involving nitrite ion (NO2-) is well known
The result of stoichiometry study for the oxidation of bromopyrogallol red by nitrite ion shows that one mole of BPR2- consumed one mole of nitrite ion
(1) Similar stoichiometry has been reported for the redox reactions of rosaniline monochloride and parafuchsin by nitrite ions respectively [4 – 6]
Summary
Oxidation-reduction reaction involving nitrite ion (NO2-) is well known. Bromopyrogallol red is of immense important because of its wide range of uses as a metal indicator for the chelatometric titration of Bi, Co(II), Ni and Pb as photometric reagents for various heavy metals and for indirect determination of anion such as halides and cyanides [2]. In spite of these and numerous other uses, redox Chemistry of this dye with NO2- has not been reported
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