Collect. Czech. Chem. Commun. 1991, 56, 1565-1574

Reduction kinetics of bromate with thiocyanate and dynamics of the closed system BrO3-/SCN-/HClO4

Ivan Valent and Ľubica Adamčíková

Department of Physical Chemistry, Comenius University, 842 15 Bratislava


The reduction kinetics of bromate ions with thiocyanate was studied polarographically and the dynamics of the BrO3-/SCN- system was studied spectrophotometrically in the medium of perchloric acid in both cases. The reduction in the presence of an at least ten-fold excess of SCN- ions is governed by the kinetics equation – d[Br(V)]/dt = a[Br(V)][SCN-][H+]2/(1 + b[SCN-]), where a = 19.2 ± 0.9 mol-3 dm9, b = 4.4 ± 0.5 mol-l dm3 at 20°C. A mechanism was proposed, based on the transfer of oxygen atom from HBrO3 to SCN- ion. The dynamic system BrO3-/SCN-/HClO4 is non-monotonous in character. According to the conditions, the production of bromine has a sigmoidal course preceded by a lag phase or the bromine concentration passes through a maximum.