SEC: AP Chemistry Labs and Learning
Students in AP Chemistry collected data on a reaction between bleach (sodium hypochlorite, NaOCl) and the food dye now known as brilliant blue. When different concentrations of bleach are mixed with the dye, the color of the mixture gradually lightens, eventually becoming clear. The intensity of the blue color can be monitored with Vernier data collection tools which can take samples every 20 seconds over a period of about 35 minutes. These 106 time points can be used to determine the rate law of this reaction, a mathematically and experimentally derived description of the reaction kinetics, a measure of the factors that contribute to the speed of the reaction. The rate law describes the relationship between the concentration of the reactants, bleach and the dye, and a rate constant, k.
The real work is not in the lab setup or data collection but in the analysis of the data afterwards. Students learned how to use their TI-84 graphing calculators to process long lists of data efficiently using three different mathematical routines, creating 9 separate graphs. The goal was to determine which mathematical routine resulted in a linear function. The mathematical routine for which this is true helps students identify how the concentration of the reactants affects the rate of the chemical reaction and can be expressed as a rate law. The AP Chemistry exam in May will assess student understanding of how various concentration vs, time graphs reveal the form of the corresponding rate law.