Revisiting the Kinetics and Mechanism of Bromate-Bromide Reaction

the bromate-bromide reaction was investigated in an acidity range not studied yet. the reaction was followed at the br2/br3- isosbestic point (l = 446 nm). it was observed a first-order behavior for bromate and bromide ions and a second-order behavior for h+ ion that results in the rate law n = k[bro3-][br- ][h+]2. this rate law suggests a mechanism involving two successive protonation of bromate followed by the interaction of the intermediate species h2bro3+ with bromide. these results disagree with the obtained by other authors who observed a second-order behavior for the bromide and first-order for h+, and have proposed intermediate species like h2br2o3 and hbr2o3-. the second-order for [h+] observed in the range 0.005 ￡ [h+] ￡ 2.77 mol l-1 sets down that the pka of bromic acid, hbro3, must be lower than -0.5 (t = 25 °c), different from all other values for this pka proposed in the literature.