A Novel Aspect of Hexacyanoferrate (III)- Iodide Ion Reaction in Acidic Medium

Abstract

Iridium(III) chloride further catalyses the oxidation of iodide ions by K3Fe(CN)6, catalyzed by hydrogen ions obtained from perchloric acid. Rate when the reaction is catalyzed only by the hydrogen ions was separated from the rate when iridium(III) and H+ions both catalyze the reaction. Separate reactions, studied in the presence as well as in the absence of IrCl3 under similar conditions were found to follow second order kinetics in [I ̄] with direct proportionality in [Fe(CN)6] ̄ and [IrCl3]. Rate was found to follow first order kinetics with respect to [H+] at low concentrations, tending to become second order at higher concentrations of [H+]. Externally added [Fe(CN)6] ̄ ions in the beginning strongly retard the rate effect, but further addition affects the rate to a little extent. Change in ionic strength has no effect on the rate. Arrhenius parameters were calculated and probable mechanisms were proposed.