Abstract
The stoichiometry, kinetics, and mechanism of the reaction between chlorite and thiosulfate have been studied at 25 °C and pH 6-9. In excess thiosulfate, the stoichiometry is 4S2032"" + C102" + 2H20 = 2S4062“ + 40H" + Cl". In excess chlorite, sulfate is produced as well, the stoichiometry being a mixture of the above reaction and S2032" + 2C102" + H20 = 2S042"
+ 2C1" + 2H+. The rate of production of OH" is d(6[OH"])/dí = /cexpt[S2032'] [C102"] [H+], but the rate constant
with the [C102"]/[S2032"] ratio, being about twice as large in excess S2032" as in excess C102". A mechanism is proposed involving the complex intermediates S203C10" and S203C1", a key reaction between the simpler intermediates S032" and CIO", and the “supercatalytic" chlorite-tetrathionate reaction. At pH » 11 in unbuffered solution, the reaction behaves as a “clock” reaction, with an initial rise in pH followed by an abrupt drop. The reaction time, however, varies irreproducibly, even in identically prepared samples. Careful analysis of the reaction time distribution and its variation with temperature, volume, reactant concentrations, and stirring rate leads to the conclusion that the switch from net OH" production to net H+ generation is induced by random fluctuations within the solution. The implications of this interpretation are discussed.