The Dushman reaction describes the interaction between iodide and iodate ions in acidic solution:

5I^- + IO₃^- + 6H⁺ → 3I₂ + 3H₂O

Under normal conditions, this reaction is in the fifth order overall, with a second-order rate law with respect to iodide (I^-). However, at micromolar I^- concentrations (approximately 5 × 10^-7 M), the reaction follows a different mechanism and becomes first order with respect to I^-. The aim of this study is to use the UV-vis spectrophotometric method to measure the rate of the reaction at micromolar I^- concentrations, and to use that rate to measure the concentration at which the rate law of the reaction changes. Seven concentrations of I^- will be tested in triplicate: for each trial, aqueous KI, KIO₃, and HClO₄ will be combined in a cuvette, and the reaction will be allowed to run to completion inside a UV-vis spectrophotometer. The initial absorbance and the absorbance at 30 seconds will be used to determine the reaction rate, and a data set comparing the rate to the initial concentration of KI will be collected. Graphing the natural logarithm of the rate versus the natural logarithm of the initial KI concentration will reveal the order of the reaction with respect to KI: the slope of the linear graph will equal the order of the reaction, and the point on the graph at which the slope changes will represent the I^- concentration of interest (expected to be near 5 × 10^-7 M). This research will serve to lend credibility to the spectrophotometric method of testing the rate of the Dushman reaction as it is used in chemical engineering (micromixing) applications, as well as providing data on which to base the usage of UV-vis spectrophotometry for other kinetic studies in a classroom or student lab setting.