KINETICS AND MECHANISM OF THE REDOX REACTION BETWEEN Pt(IV) CHLORIDE COMPLEX IONS AND SODIUM THIOSULFATE IN AQUEOUS SOLUTION. PART I: ACIDIC SOLUTION

In this work, spectrophotometric studies of the kinetics and mechanism of reaction between [PtCl6](2-) complex ions and sodium thiosulfate, were carried out. The influence of different conditions, such as: initial concentrations of reductant and platinum(IV) complex ions, ionic strength, pH and temperature on the rate constant, was experimentally determined. From the obtained results, the molecularity of the first elementary step, value of the enthalpy and entropy of activation in Eyring equation as well as corresponding rate equation, were experimentally determined. It was found that the reaction is relatively slow and leads to the S, Pt and PtS colloids formation. The best conditions for solid phase formation containing Pt are at pH = 5.