Passage I

Hydrogen peroxide (H₂O₂) decomposes in the presence of the enzyme catalase, producing H₂O and oxygen gas (O₂) according to the balanced chemical equation

2H₂O₂ 2H₂O + O₂

Students performed 2 experiments to study this decomposition. In each trial of the experiments, Steps 1− 3 were performed:

1. A fresh, circular piece of filter paper with a diameter of 6.0 mm was immersed for 2 min in an aqueous catalase solution maintained at a certain pH.

2. The filter paper was removed from the solution. Then a glass rod was used to quickly push the filter paper to the bottom of a beaker containing 500 mL of a freshly prepared aqueous solution having a certain concentration of H₂O₂ (see Figure 1).

3. Once the filter paper reached the bottom of the beaker, the glass rod was immediately removed, and gas bubbles from the reaction surrounded the filter paper, causing it to rise to the surface of the solution. The rising time , RT (the time required for the filter paper to rise to the surface), was recorded.

Experiment 1

In Trials 1−5, H₂O₂ solutions that differed in concentration (percent H₂O₂ by volume) were tested while the catalase solution was maintained at a pH of 6. The results are shown in Table 1.

Experiment 2

Trials 1−5 were repeated 3 times, except that in each set of trials, a different pH was tested. The results are shown in Table 2.

Figure and tables adapted from K. A. Johnson, "A Simple Method for Demonstrating Enzyme Kinetics Using Catalase from Beef Liver Extract." ©2000 by the Division of Chemical Education, Inc., American Chemical Society.