The standard electrode potential of the Sn~(4+)/Sn~(2+) couple revisited

摘要

The Sn~(4+)/Sn~(2+) redox couple is, thermody-namically, the connecting link between aqueous tin(IV) and tin(II) chemistry. Because the equilibrium potential E°(Sn~(4+)/Sn~(2+)) was not known with sufficient accuracy, we were prompted to attempt its determination by means of a potentiometric study. The equilibrium potential of the redox couple Sn~(4+)/Sn~(2+) has been determined in x M HClO4 + 1 M HCl media (x = 3, 4, 5). The formal potentials determined for different electrolyte mixtures were extrapolated to zero ionic strength by the extended specific ion interaction theory approach (E°(Sn~(4+)/ Sn~(2+)) = 0.384 ± 0.020 V). The evaluation of the data required knowledge of the formation constants of tin(IV) chloro complexes; these were determined spectrophoto-metrically at five different HClO4 concentrations (4.5-8.0 M), and were extrapolated to zero ionic strength.