The oxidation of potassium hexacyanoferrate(II)trihydrate by potassium dibromodicyanoaurate(III) in acidic solution: a kinetic study

Abstract

Abstract The reduction of the dibromodicyanoaurate(III) ion by hexacyanoferrate(II)trihydrate was studied in an acidic medium. The reaction was first order in both Au(CN) 2 Br 2 − and Fe(CN) 6 4− and a second order rate constant of k 2 = 255 ± 5 M −1 s −1 at [H + ] = 2.041 × 10 −4 M, an ionic strength of 0.51 M (NaBr) and 20.0 ± 0.1 °C was found for the reaction. The reaction rate decreases with increasing [H + ] in the region 0.0004 ≤ [H + ] ≤ 0.065 M. An equilibrium constant of K a = (3.00 ± 0.01) × 10 −3 M (pK a = 2.52) at 20.0 ± 0.1 °C was found for the deprotonation of H 2 Fe(CN) 6 2− . Activation parameters of ∆H # = 47.8 ± 0.9 kJ mol −1 and ∆S # = −37 ± 3 J K −1 mol −1 have been obtained by a least squares fit of temperature data directly to the Eyring equation. Graphical abstract