Detailed Studies of Propagating Fronts in the Iodate Oxidation of Arsenous Acid

In an unstirred thin film of solution containing iodate and arsenous acid, a single propagating wave of chemical reactivity may be exhibited. The wave converts the solution from colorless to blue in reaction mixtures containing iodate in stoichiometric excess and starch indicator. The wave appears as a narrow blue band propagating through a colorless solution in reaction mixtures containing arsenous acid in stoichiometric excess. Waves were electrochemically initiated and propagation velocity was measured as a function of reactant concentrations. Iodide concentration was measured with an iodide selective microelectrode as a wave passed through the electrode position. The reaction-diffusion behavior is explained with a simple reaction mechanism autocatalytic in iodide.