Enzyme Catalase Lab
Title: The Effect of pH on Rate of Catalase Catalyzed Reactions
Purpose: To test the effects of the pH on the rate of reactions catalyzed by catalase
Background: Enzymes are proteins produced by living cells that act like catalysts in chemical reactions. Catalysts are molecules that increase the speed of chemical reactions by decreasing the activation energy of a reaction. Catalase (the peroxidase enzyme) is especially concentrated in the livers of animals and works by converting the substrate Hydrogen Peroxide (H2O2) into water (2H2O) and oxygen gas (O2). In order for the enzyme to work under ideal conditions, the catalase should have a neutral pH of 7. The balanced equation for this decomposition reaction is 2H2O2 –> 2H2O + O2. In order for the enzyme to work under ideal conditions, the catalase should have a neutral pH of 7. The catalase becomes denatured, which means that it is in an unsustainable environment and the shape of the molecule is altered, so the catalase will not function as an enzyme if the solution is too basic or too acidic.
Hypothesis: If the pH of the H2O2 solution has an effect on the rate of the catalase reaction, then the rate of the reaction will decrease as the pH becomes increasingly acidic.
© Based on and recreated from diagram by Madison Schmidt
- Fill a graduated tube with 10mL of H2O2 and 350mL H2O in an upright position.
- Fill two beakers with 200mL of water.
- Put the graduated tube with the hole through the bottom in one of the tubes (upside down tube).
- Attach the end of the clear plastic pipe through the hole in the graduated tube in the water.
- Attach the opposite end of the pipe to the lid of the other graduated tube containing H2O2 (right side up tube).
- Place two binder clips on the pipe, each clip an equidistance between the tube and the middle of the entire pipe. (Shown above).
- Add the acid (lemon juice) to the H2O2.
- Immediately remove the binder clips and begin the timer.
- Hold the graduated tube steadily in the water and in such a way that it can be read legibly. Do not move the tube.
- Record the amount of O2 that fills the tube, (is evident as the water level drops) ; and record it written in time increments of 10’s, 20’s, and 100’s. (Shown below).
- Clean and rise all equipment before repeating steps 1-9 for two remaining trials.
Analysis: As the pH of the solution became increasingly acidic, the water dropped at a slower rate which meant that less oxygen gas was being produced. The lowest pH level caused no reaction, the pH of 2.5 had the slowest reaction rate, and the pH of 4.7 produced the highest amount of O2 gas. The optimal pH out of the 3 chosen for the catalase was the pH of 4.7, because the water dropped in the fastest rate, meaning that it was the most efficient pH in producing oxygen gas.
Conclusion: The data collected above supported the hypothesis that if the pH of the H2O2 solution had an effect on the rate of the catalase reaction, then the rate of the reaction would decrease as the pH becomes increasingly acidic. Enzymes have ideal conditions, so the catalase works best when it has a neutral pH (pH of 7), and is inactive when the solution is too acidic or basic.
The pH of 4.7 was the closest to neutrality in this experiment, so as a result, this number was the baseline created. However 4.7 is not equal to 7, so the conditions for the enzyme were still not standard. The enzyme catalase has many optimum conditions for pH, temperature, concentration, and inhibitors. The purpose of this experiment was to test the effects of the pH on the rate of catalase reactions. The most acidic pH used in this experiment had a pH of 2.5, and was unable to break down the hydrogen peroxide (H2O2) and no reaction took place. The pH of 3.4 broke down at a greater rate than the pH of 2.5, however it was still a slow reaction and the rate of the reaction decreased. The pH closest to neutrality (pH of 7) was the pH of 4.7, which was able to break down the H2O2 and the rate of reaction was higher and faster than the preceding pH levels were. After 160 seconds in each reaction, the catalase in the solution of 2.5 pH had produced 0 mL of O2 gas, the catalase in the solution of 3.4 pH had produced .25 mL of O2 gas, and the catalase in the solution of 4.7 pH had produced 5.5 mL of O2 gas. This data supports the hypothesis that if the pH of the H2O2 solution has an effect on the rate of the catalase reaction, then the rate of the reaction will decrease as the pH becomes increasingly acidic. This is because the H2O2 concentration became denatured (changed molecular shape and could not function property) as the pH became increasingly acidic, providing evidence that the catalase works best in less acidic/neutral conditions.
All of the pieces of data collected support the hypothesis, but because the experiment did not build up to the optimum pH condition for catalase, standard results are not present in the data. However, the data does show that the pH has a large effect on the rate of catalase reactions.
- Posted in: Investigations