Determining Reaction Orders by Measuring Half-Life

In a three-hour laboratory experiment suitable for advanced high school or first-year college chemistry courses, students measure the half-lives of reactions between FD&C Blue #1 food coloring and sodium hypochlorite to determine the order of reaction with respect to each reactant. The half-life relationships are simplified by maintaining hypochlorite at a much greater concentration than the dye. Using measured half-lives to determine reaction orders not only gives students direct experience of the meaning of half-life, but also allows them to interpret the results of the experiment in a simple, rapid fashion. Unlike typical kinetics experiments, only a few data points need to be gathered and most of the significant data interpretation can be done by the students while still in labortory and without the aid of graphing software, yet the results are generally quite good.