A kinetic study of the reaction between soluble (colloidal) manganese dioxide and formic acid

Abstract

The kinetics of the reaction between a soluble form of colloidal manganese dioxide (obtained by reduction of potassium permanganate with sodium thiosulfate) and formic acid in aqueous perchloric acid solution has been investigated by UV—Vis spectrophotometry. The rate law is r = (k+k ′[H +] 1.67)[MnO 2][HCOOH] 0.45 The apparent values found for the activation parameters are E a = 53.6 ± 0.8 kJ mole −1, Δ H ≠ = 51.1 ± 0.8 kJ mole −1, and Δ S ≠ = −140 ± 3 J K −1 mole −1. The reaction seems not to be very sensitive toward addition of sodium perchlorate to the solution, but is noticeably retarded by addition of gum arabic acting as a protective colloid. A mechanism in accordance with the experimental results is proposed for the reaction taking place at the colloid surface.