Method:
- Collect all the apparatus mentioned in the section above.
- Cut 5 disks of potato using a scalpel into equal sized 2mm discs. Place these in the boiling tube, and place this boiling tube on a test tube rack.
- Also, collect a 250ml beaker and fill approximately 2 thirds of it with water. Put in the collecting tube and use a syringe to suck up some water into it, note down the volume. With a bung tighten the collecting tube to ensure that water and oxygen do not leave it.
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Add 5 cm3 hydrogen peroxide solutions to the potato disks.
- Without delay place the bung and delivery tube firmly into the boiling tube, place the other end of the delivery tube under the collecting tube (ensure that the bung is secure so no oxygen escapes).
- Start the timer as soon as the first bubble of oxygen enters the collecting tube from the delivery tube.
- During the three minutes, shake the boiling tube gently throughout the reaction to ensure that the contents are well mixed.
- Measure the volume of oxygen produced in the three-minute period and so the change in volume, the reading must be taken at eye level to ensure you are reading the scale correctly.
- For the rest of the experiment repeat the above steps but with a different number of potato discs, make sure that you wash out all apparatus to prevent contamination by impurities. Make sure all the conditions are unchanged making the test results more valid.
Variables:
Independent Variable: Number of potato discs, surface area of potato discs
Increasing the surface area of the potato discs, and also the number of potato discs containing the catalase will mean that more catalase molecules are open to the elements of the hydrogen peroxide solution. The rate of reaction will therefore, increase, due to the increase in successful collisions. I aim to control this variable by cutting the potato discs the same size I aim to do this by cutting the potato discs using a cm ruler.
Dependent Variable: Amount of oxygen and has produced
I cannot control this, in this experiment I only aim to measure it, so that I can be secure in my conclusion.
Control Variables:
Hydrogen Peroxide volume and concentration
These affect the rate of reaction as when there is more substrate concentration (Hydrogen Peroxide) there is an increase in the rate of reaction. For this reason I aim to control the substrate concentration by using the same quantities and concentration of the substrate Hydrogen Peroxide for each different experiment with different amounts of discs.
pH level:
It is essential to control the pH level as a change in pH would affect the ionic and hydrogen bonding in an enzyme and so it would alters its shape and its active site so the reaction may not be catalysed. Every enzyme has an optimum pH at which its active site best fits the substrate and the reaction is catalysed. Difference either side of the optimum pH, results in unwanted conditions of the enzyme and a slower rate of reaction, which would make my results unreliable if this was different in every reaction, for this reason it is essential that I control this variable. To control this in my experiment I will use potato discs from the same potato this means the pH level will be controlled as the same potato throughout on average will have the same pH, also the same quantity of Hydrogen Peroxide was used for each experiment. This acid maintained a pH level which was suited to the enzyme, as it was similar to the natural pH of the enzyme (the potato).
Temperature:
As temperature increases, molecules move faster as they have more kinetic energy, this means that the reaction if it is warmer will be catalysed quicker, and the reaction will happen at a quicker rate, in the same way if the temperature is too high the enzyme catalyse (the potato) can denature and the reaction will not take place as the substrates shape will be altered. Therefore, for these reasons I will aim to control this variable by doing the experiment in the same room so that the difference in temperature is minimal.
Results:
Conclusion:
From my table of results I can see that as the number of potato discs increases, and therefore, the surface area of the enzyme increases, so does the amount of oxygen and water produced. I believe this is due to their being an increase in the enzyme therefore there are more enzyme active sites to react with the substrate hydrogen peroxide. This means that more collisions will take place, and therefore more oxygen and water will be released.
Evaluation:
My results are fairly accurate; I can infer this from the closeness of my set of results in the results table. From the graph I can see that my results are accurate and reliable as most values are in the line of best fit however, I do notice that for my 3rd experiment with 4 potato discs the value is not on the line of best fit, below I will explain any reasons for these outliers.
I believe the procedure in which I carried out the experiment was quite precise; however, I did get 1 outlier, this could be due to many reasons, for example the volume of hydrogen peroxide sometimes did not cover all of the potato discs meaning a full reaction did not occur, so if I was to redo this experiment I would add more volume to the solution. Furthermore, if I was to redo this experiment I would also a greater variance in potato discs, for example if I was to use a variance of 1-20 potato discs I would be able to obtain more precise and accurate results as I would get a better average and would make my conclusion more secure. Although I measure the difference in volume and therefore how much oxygen was released, I am not completely sure that this gas released is oxygen so to make my experiment more reliable if I was to redo it I would test the gas collected, to ensure that it is oxygen. I would do this by lighting a tongue depressor with the match (as oxygen is usually needed for combustion) and blow at the flames, so that a glowing ember remains, and the embers should cause it to burn at a quicker rate. Moreover, If I was to do the experiment again I would measure the potato pieces using a micrometer, this would provide a more accurate sized piece of potato and this would mean a much more accurate set of results.
Additionally, if I was to redo this experiment I would also repeat each experiment, as I only did one experiment for each number of potato discs however, if I was to do more repeats I would have a better average as I would have more results and therefore my results would be more reliable. Despite these minor mistakes I am confident in my conclusion as most of my results follow a pattern and the procedure in which the experiment was taken out, is pretty accurate. Finally, the potato discs may have stuck to each other, blocking one of the ends from releasing enzymes, this means that a full reaction may not occur and I will not get accurate results due to this, so if I was to redo this experiment I would ensure that the potatoes are touching each other as little as possible.
All in all, from this experiment I have learnt that an increase in the number of potato’s, and therefore an increase in surface area (an increase in the enzyme catalase) there is more gas and water produced
