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 = k1K1K2K3K4[Cl]/[H3O+]([H3O+ ] + K1) (i) (i) where K1;K2,K3 and K4 are the respective equilibrium constants of the reactions (ii) to (v) and kj is the rate constant of the slow complementary two HAuCl4 + H2O ⇄ AuCl4- + H3O+ K2 (ii) AuCl4-+H2O⇄ AuCl3 (OH)- + H3O+ + Cl- K2 (iii) SbCl4- + Cl- ⇄ SbCl52- K3 (iv) SbCl52- + Cl- ⇄ SbCl63- K4 (v) electron transfer step of the reaction between the active species AuCl3(OH)- and SbCl63- 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.