Photochemical after-effect in H₂O₂-K₄Fe(CN)₆ reaction

Abstract

The dark reaction between hydrogen peroxide and a pure dilute aqueous solution of potassium ferrocyanide has been critically examined. The experiments described in the paper lead to the conclusion that potassium aquopentacyanoferrite produced as a substitution product in very minute concentration in aqueous ferrocyanide in the dark reacts with hydrogen peroxide resulting in the measured dark reaction. Aged solutions of ferrocyanide, as well as pre-heated and pre-illuminated solutions used sometime after treatment show a distinctly lower rate of peroxide decomposition. This diminished reactivity towards hydrogen peroxide appears to be due to the partial decomposition of the aquo-complex salt by heat, prolonged exposure to light and ageing. The marked photochemical after-effect observed in the pre-insolated mixture of hydrogen peroxide and potassium ferrocyanide has been studied in detail with varying periods of pre-illumination of the reaction mixture. It is found that the greater the period of pre-illumination of the mixture, the greater is the photochemical after-effect within the concentration limits of reactants used in the experiments.