Role of trace iron(III) and equilibrium Fe(III) + Fe(CN)<img src='http://www.niscair.res.in/jinfo/equation29.gif' border=0> <img src='http://www.niscair.res.in/jinfo/harpoon.gif' border=0> Fe(II) +Fe(CN)<img src='http://www.niscair.res.in/jinfo/threebysix.gif' border=0> in the investigation on kinetics and mechanism of oxidation of hexacyanoferrate( II) by peroxodiphosphate in acid perchlorate solution

Abstract

Oxidation of hexacyanoferrate(ll) with peroxodiphosphate(pdp) in aqueous perchloric acid solutions occurs through the catalysis by Fe(III) present in traces in the reagents and distilled water involving the equilibrium. Fe(III) + Fe(CN)<img src='http://www.niscair.res.in/jinfo/equation29.gif' border=0> <img src='http://www.niscair.res.in/jinfo/harpoon.gif' border=0> Fe(ll) + Fe(CN)<img src='http://www.niscair.res.in/jinfo/threebysix.gif' border=0>. Fe(ll) is oxidised back to Fe(III) by pdp in the fast step. The rate law is <em>d</em>[Fe(CN)<img src='http://www.niscair.res.in/jinfo/threebysix.gif' border=0>]/<em>dt </em><em>=((k₁ </em> + k_d/[H⁺]) [Fe(Ill)][Fe(CN)<img src='http://www.niscair.res.in/jinfo/equation29.gif' border=0>].The values of <em>k₁</em> and <em>k_d </em>have been found to be 5.7 x 10³dm³ mol^-1 s^-1 and 36 s^-1 respectively at <em>I</em> = 0.5 mol dm^{- 3}and 30°. The equilibrium constant for the above equilibrium determined spectrophotometrically is 34 ± 4 at 28°, <i>I</i> = 0.05 mol dm^-3 and [H⁺] = 0.01 mol dm^-3. Aquo copper(II) retards the rate of oxidation of Fe(CN)<img src='http://www.niscair.res.in/jinfo/equation29.gif' border=0> by pdp. Spectrophotometrically too the equilibrium is shifted to the left in the presence of Cu(II).