Experiment 11 - Kinetics of Food Dyes >> Step 3: Determine the effect of bleach on the reaction

Experiment 11 - Kinetics of Food Dyes

Step 3. Designing a research project to determine the order with respect to bleach.

Let's summarize what we discovered until now.

In Step 1 we discovered that the more concentrated the bleach, the faster the colour of dye disappeared.

In Step 2 we established that:

• Rate = k' [dye] and
• k' = k [bleach]ⁿ

As the bleach is colourless, you will not be able to determine directly what happens to it in the reaction, however, you will be able to deduce the effect of bleach by analyzing the equation k' = k [bleach]ⁿ : how the concentration of excess bleach influences the rate of reaction.

This rate of the reaction can again be determined from a kinetic trace of the absorbance of the solution, since this tells us how rapidly the dye disappears. From your first experiment you know the order of the reaction in dye, and the pseudo-rate constant, k'. Pseudo indicates that k' is a product of the actual rate constant, k, and the concentration of bleach, k'= k [bleach]ⁿ. Think about what happens to the pseudo-constant, k', when you change the concentration of bleach.

Consider the hypotheses corresponding to the reaction being zeroth, first or second order in bleach. For each of these three hypotheses, what would be the effect on the kinetic trace of changing the concentration of bleach? Design an experiment that you can use to decide which hypothesis is supported.

Write down your experiment, and how it will allow you select the correct hypothesis, on your feedback form.

Write a short procedure for the experiment(s) you will perform to test your hypotheses. Use the simulation to perform the experiment.

On you feedback form, prepare a Results table for this part of experiment. Enter your results there. What is the order in bleach?

Explain your conclusions.

Print out the appropriate graph to hand in to your TA.