Kinetics of Oxidation of Antimony(III) by Tetrachloroaurate(III) in Aqueous Hydrochloric Acid Media

Abstract

The oxidation of antimony(III) by tetrachloraurate(III) has been studied in aqueous hydrochloric acid medium at 27°C. The reaction follows the rate law ks = k 1 K 1 K 2 K 3 K 4 [Cl]/[H 3 O + ]([H 3 O + ] + K 1 ) (i) (i) where K 1 ;K 2 ,K 3 and K 4 are the respective equilibrium constants of the reactions (ii) to (v) and kj is the rate constant of the slow complementary two HAuCl 4 + H 2 O ⇄ AuCl 4 - + H 3 O + K 2 (ii) AuCl 4 - +H 2 O⇄ AuCl 3 (OH) - + H 3 O + + Cl - K 2 (iii) SbCl 4 - + Cl - ⇄ SbCl 52- K 3 (iv) SbCl 5 2- + Cl - ⇄ SbCl 6 3- K 4 (v) electron transfer step of the reaction between the active species AuCl 3 (OH) - and SbCl 6 3- of the reactants. The enthalpy and entropy of activation were found to be 19.2 ± 1 kj mol -1 and - 182.5 ± 4 JK -1 mol -1 respectively,suggesting a chorobridged electron transfer.