Kinetics of the bromate–iodide reaction: catalysis by acetate and other carboxylate ions
Abstract
A direct amperometric method for continuous determination of iodine concentrations of the order of 10–5M was used to investigate the kinetics of the bromate–iodide reaction. Marked catalysis by buffer anions was discovered. The rate law was found to be v=-d[BrO3–]/dt=k0[H+]2[BrO3–][I–]+kb[B–][H+]2[BrO3–][I–]. At 25° and ionic strength 1·00M in a perchlorate medium, k0= 49 M–3 sec.–1, and for B–= acetate, β-chloropropionate, and chloroacetate, kb= 5·4 × 104, 1·7 × 104, and 2·5 × 103M–4 sec.–1 respectively. For acetate solutions more concentrated than 0·05M the second term predominated. The mechanism is discussed, and it is shown that the intermediate BrO2+ is unlikely to exist. Reaction schemes are proposed involving additions and replacements on the bromate ion.
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