The effect that potato surface area and Hydrogen Peroxide concentration have on the rate of reaction for the enzyme catalase

The formula for this reaction is:

2H2O2 › 2H2O + O2

*An enzyme is a biological catalyst. A catalyst provides a surface for a reaction but does not actually take place in the reaction itself. There are two types of enzyme, breaker and builder enzymes. Breaker enzymes split a substrate into smaller parts and builder enzymes combine multiple substrates into a single one.

Equipment:

I will use to following equipment for my experiments:

- Large bowl half filled with water

- 2 X 100ml Conical flasks

- Rubber bung and tube

- 2 X 100ml Measuring cylinders

- Different concentrations of hydrogen peroxide

- Potatoes

- Stopwatch

- Size 5 metal bore

Method:

The equipment was set up as shown in the diagram above. A circular cross section of the potato measuring 10mm was cut out using the bore. The diameter of the number 5 bore was also 10mm. This piece of potato was then be put into a conical flask filled with 40ml of hydrogen peroxide and the amount of gas given off after 10minutes (600 seconds) measured for five different concentrations of hydrogen peroxide. These concentrations were 5%, 10%, 15%, 20%, 25% and a control, which consisted only of water (0% hydrogen peroxide). The experiment for each concentration was then repeated three times and an average taken to ensure accuracy. To ensure that the test was as fair as possible the only criterion that was changed was the concentration/molarity of the hydrogen peroxide solution. The volume of the hydrogen peroxide solution and the room temperature were maintained as constant as possible.

Criteria Changed

Criteria Kept The Same

Concentration of H2O2

pH Value

Temperature

Potato Surface Area

Weight of Potato

Prediction:

My prediction was that as the molarity or the concentration of hydrogen peroxide increases the rate of reaction would also increase proportionally. This was because the higher the concentration the more molecules of hydrogen peroxide there would be compared to the water in the solution. The particle theory states that the more molecules of hydrogen peroxide there are the greater the chance they will collide with the enzyme and be taken into its active site. As more enzymes arrive at the active site, more will be broken down into oxygen (and water) so at the end of ten minutes more oxygen will have accumulated in the measuring cylinder. Should the concentration reach a point at which all the active sites are being used than the reaction will level off and remain constant. I predicted that the higher the concentration of hydrogen peroxide the more oxygen would be collected in the measuring cylinder at the end of the experiment and that the control would not produce any oxygen.

Results:

Oxygen After 600 Seconds (ml)

0%

5%

0%

5%

20%

25%

Experiment One

0

9

4

20

23

28

Experiment Two

0

8

6

9

26

31

Experiment Three

0

0

5

20

24

29

Average

0

9

5

9.7

24.3

29.3

These results show that as the concentration of hydrogen peroxide increases so does the amount of oxygen collected from the test tube. I predicted that as the concentration increased the amount of oxygen collected in the measuring cylinder would also increase proportionally. This is clearly shown on my graphs through the lines of best fit and how close they are. The reason for this relationship is that a higher concentration means there are more hydrogen peroxide particles in the solution. More hydrogen peroxide molecules in the same volume of solution means that there will be more collisions between the hydrogen peroxide molecules and the catalase enzymes, increasing the chance that a hydrogen peroxide molecule will reach the active site of a catalase enzyme so it can be broken down. More hydrogen peroxide being broken down produces more oxygen as one of the products of the reaction. The oxygen is then collected in the measuring cylinder so if a greater concentration produces more oxygen in the same time as a lower concentration there will be more oxygen in the measuring cylinder for the greater concentration after the 600 seconds are up. This result conforms to the prediction I have explained earlier.

Evaluation:

The results obtained from my experiment were reliable since the points on my graph are close together for each of the concentrations. The lines of best fit are close together, which shows close results and good reliability. The lines are also straight indicating a direct relationship between concentration and the amount of oxygen collected. There were two anomalous results, both for the 25% concentration, which are shown on my graph furthest away from the line of best fit. These results could be indicating that the enzyme active sites are reaching full capacity as I outline in my prediction. In order to test this I could repeat the experiment but use concentrations of 30%, 35%, 40% and 45% as well. To improve the overall reliability of the experiment I could use a gas syringe to collect the oxygen instead of a measuring cylinder, as the gas syringe would be more accurate at measuring the amount of oxygen given off, measuring the amount to 1d.p reliably. Using a computer program to measure the amount of gas in the syringe with more specialised equipment would yield a further increase in accuracy. Analysing the results for this experiment, even taking anomalies into account the reliability of the results is still good since the amount of oxygen collected in all three repeats are quite close, perhaps measuring to 1d.p with a more reliable method would reveal a closer connection. The anomalies could be caused by the rate of reaction stabilising since the active sites on the catalase enzyme may be reaching saturation point and become unable to accept more hydrogen peroxide molecules. As additional work to further my investigation into enzymes I could do similar experiments to calculate the rate of reaction for other enzymes such as amylase and protease and compare them.