A study of the kinetics and mechanisms of perbromate-bromide oxidation-reduction reaction.

Abstract

The goal of this research project was to study the perbromate-bromide oxidation-reduction reaction. Earlier studies have indicated perbromate is quite sluggish in its reaction. This inertness of the perbromate ion stands in sharp contrast to its high thermodynamic oxidizing power which is greater than that of any other oxyhalite ion that exist in aqueous solution. The reaction of perbromate ion with a number of two-equivalent reductants have been studied in aqueous solution at an ionic strength of approximately one. This research investigated the kinetics of the perbromate-bromide reaction. Oxygen transfer from perbromate to bromide may be the key step in the mechanism of this reaction. Experiments were carried out at CH+] = 0.25 x 10-· -1.00 x 10-· M, temperature at 326.7, 331.2, 336.2 and 341.2 K and a constant ionic strength of 0.20 adjusted with NaCIO. The rate law dCBr3-J/dt = kCBrO~-HBr-J. CW]· was confirmed. From the rate law, rate constants at several temperatures were calculated and the activation energy was determined to be 16.8 Kcal/mol. The results were also compared to the data of analogous oxyhalite reactions from both experiment and literature. The kinetic salt effect was also investigated by comparing rates at several different ionic strengths varying from 0.10 to 0.50 M. The results were consistent with the Bronsted-Bjerrum relationship and the Debye-Huckel constant is -0.41.