Collection of Czechoslovak Chemical Communications - digital archive 

Abstract

Kinetics of Fe(II) oxidation by chlorate was studied in homogeneous systems (pH 1, HCLO₄ and in heterogeneous systems involving precipitate of Fe(III) hydrolysis products (pH 1 to 5.5). The stoichiometry ( 6 Fe²⁺ : 1 ClO^-₃ : 6H⁺) as well as the rate equation (-d[Fe²⁺]/dt = k_exp/.[Fe²⁺][ClO^-₃]) is the same in the two cases. Also the differences in the experimental activation energies and entropies for the two pH regions are insignificant. The [OH^-]/[Fe³⁺] ratio passes a maximum during the spontaneous change of pH (pH₀ 5), whereas if the pH is maintained constant (pH 5) the ratio increases monotonically throughout the whole time interval followed. The balance of the Fe²⁺ and Fe³⁺ showed that part of the Fe²⁺ ( 10^-3 mol l^-1) was present during the reaction in the precipitate of the Fe(III) hydrolysis products, while part of the Fe³⁺ (5 . 10^-3 mol l^-1) existed outside this precipitate; the latter dropped by approximately two orders of magnitude only several tens of hours after the finishing of the Fe(II) oxidation.