Timing the Color Change

Purpose

The purpose of this experiment is to discover the behavior of the oscillating reaction. Are their periods? What are they? Are these periods regular or not? What is their shape in time? It is proposed that the behavior of the system be found by observing one particular color change and timing it. If there are enough people then it may be possible to time two color changes. It is also a purpose to obtain quantitative measures of periods, or quasi-periods, by having several observers make measurements and then finding an average.

Work in small groups

The Sequence of Events:

  • describe in words what is happening
  • from this observation decide what variables are appropriate for data collection
  • collect data
  • analyze data
  • propose a mathematical model to express the data
  • compare the experimental data with the mathematical model
  • suggest refinements to the mathematical model
  • suggest new experiments based on the existing data and the model

    If there are several groups of observers then we may determine a group average of the period as well as an overall grand aveage. The spread of these measurements lets us know something about their validity. This also teaches us something about measurement and statistics.

    Experimental Setup

    Listed below is a movie of the Belusov-Zhabotinsky reaction at a temperature of 22 C. This may be used to develop experimental data if it is inconvenient to actually run the reaction. The movie has been digitized. This is a developing section. Current resolution may be poor and the image is small. Please be patient.

    If you need a movie viewer for the Mac click on this.

    Experiment 3: 74C-900K .

    Review laboratory safety and techniques

    First set (and measure) the temperature of the reaction mixtures to room temperature, 20C or 68F. Among other things we want to investigate how the reaction depends on temperature.

    Mix the three solutions in a large beaker placed on a magnetic stirrer and at the time when complete mixing has occurred start timing the color change. Pick a color of interest, say blue, and mark the time of the most intense color. Record these times and enter them in a spread sheet.

    Data Treatment

    Each group should have collected three sets of data for a number of time periods during the extent of the oscillating reaction. Each observer should average their total set of times and each group should make an average of each period time. An average and an standard deviation should be recorded. The easiest way to do this is to use a spread sheet on a computer.

    For a more sophisticated discussion of data analysis go to statistics

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