A study of the electron exchange reaction between Tin(II) and Tin(IV) in aqueous sulfuric acid solutions

The kinetics of the exchange reaction between tin(I I) and tin(IV) in aqueous sulfuric acid were studied in the temperature range of 25 to 50 degrees. Experiments were designed to determine the effects of variation in concentration of tin(II), tin(IV) (SO4-), (H+) and (Cl-) ions. It was found that the reaction is first order,Lvith respect to tin(II) and tin(IV) and that the effect of increasing (H+) is to decrease the rate of exchange, and the effect of increasing (SO4-) is to increase the rate of exchange. An empirical equation, R/ab = 0.674 (H+)(-2) + 0.0725 (SO4-)(H+)(-1), which predicts the effects of (H+) and (SO4-) on the rate of exchange is presented and some possible mechanisms which lead to this model are discussed. The addition of (Cl-) to the reaction mixture in 3.00 m H2SO4 increases the rate by up to a factor of 100. The rate can be Falculated by the equation, R = 4.94[Sn(II)][Sn(IV)][Cl-], above 0.5 M Cl-, and a mechanism which leads to this model is given. Spectrophotometric examination of aqueous solutions of tin(II) in either HClO4 or H2SO4 have been interpreted in terms of the hydrolysis of Sn++. The concentration hydrolysis constant, equal to 24.5, has been evaluated. The absorption of tin(IV) solutions and tin(II)-tin(IV) solutions in 3.00 11 H2SO4. and tin(II)-tin(IV) solutions in H2SO4. containing 1.00 M Cl- (3.99 M H+) are given. The spectra have been interpreted in terms of interaction dimers containing one atom of tin(II) and one atom of tin(IV).