Dissolution of bismuth metal by tri-iodide ion in acidified potassium iodide solution

Dissolution of bismuth metal by tri-iodide ion in acidified potassium iodide medium has been studied using a rotating disc technique. The rate constant for the dissolution process, k T , in solutions 0.5 M in potassium iodide at 25.0 °C has been shown to be related to the square root of the disc angular velocity, ω, by the following expression[Formula: see text]The activation energy for this reaction was found to be 4.7 kcal mole −1 . These data clearly establish that the rate of dissolution is determined by the rate at which tri-iodide ion is transported to the metal surface. In solutions of [KI] = 0.10 M, however, the rate determining step appears to involve diffusion of tri-iodide ion through a layer of BiI 3 which forms on the bismuth metal surface as the reaction proceeds.