To make this a fair test, we need to keep the same all variables that could affect the outcome except for the one being tested, temperature. So the pH, amount of solutions used, concentration of solutions, apparatus etc. must all remain the same.
As my source of Catalase, I will use potato. This is easier to cut and measure than other sources such as liver, which would be hard to cut into equal pieces. The potato “chip” will be pre-warmed in a boiling tube in a water bath of each temperature for 10 minutes, as will 20cm3 of H2O2. Once the desired temperature is reached, the chip and H2O2 will be mixed in the boiling tube, shook a couple of times and placed back in the water bath with a rubber bung on top with a tube coming out. This tube is connected to a burette of water whose bottom is submerged in a bowl of water. I will measure the amount of oxygen produced by recording the starting level of the burette and the end level, and finding the difference, making sure I read it level with the markings to avoid parallax error. The time will run for 3 minutes from when the first bubble is seen rising up the burette. This will all be done twice.
I will keep this experiment safe by adhering to all normal laboratory rules, such as safety glasses, not running in the lab and so on.
The apparatus will be set out as shown below:
Preliminary Work
I did a preliminary experiment to give me an idea as to which values and range I should use for my temperatures, and to check if the equipment and setup I had chosen was suitable for the experiment.
Here are the results of that experiment:
These results are not ideal, as they have only been done once so no averages can be found to improve accuracy, but they give me an idea as to which values to use as my temperatures. It does show however that Catalase seems to start denaturing at around 60°C, and that it appears to work best at around 50°C.
Table Of Results For Main Experiment
Analysis
The table and graph show that as temperature increases, so does the speed of the reaction, as the amount of oxygen produced is getting bigger. This is because as the temperature rises, the particles have more energy and move faster, and therefore collide more often, causing the reaction to take place more times (this is the particle theory.) This relationship is true, except for when it goes from around 55°C down to around 70°C, the rate gets slower. This is due to the fact that the enzyme is denaturing during this period.
The graph does not appear to show any kind of quantitative result, but it does show that temperature rise does increase rate of reaction, and it also shows the area where the enzyme is denatured – the sharp drop between around 50-60°C, slowly down to 0.0cm3 at 69°C.
Evaluation
I think that my results are quite accurate, as I took care when recording the results, measured amounts carefully and carried out the experiment as carefully as possible. I do not think there are any anomalous results, as the points lie on or very near to the best-fit line.
This experiment has some faults. Firstly, as soon as the Catalase comes into contact with the H2O2, it starts to lose its concentration as the Catalase is used up in the reaction and therefore becomes less concentrated towards the end of the reaction. This cannot really be helped unless there was a way of keeping the concentration the same all the way through the whole of the experiment, maybe by adding more potato as it starts to run out.
The equipment could be improved. A syringe with a needle may be used to inject the H2O2 through the bung directly into the boiling so that there is no lag time for the oxygen to escape while the bung is being put on the tube. I think the evidence I have is strong enough to support the conclusion “as the temperature rises, the rate of reaction increases except where the enzyme is denatured,” but not strong enough to give a quantitative result. This could be achieved by using more sophisticated equipment so that no oxygen was lost at all, and testing it several times instead of just two or three times.
More evidence could be acquired by carrying out more experiments. This could be to get a more accurate reading of points not tested here, such as 55°C or 15°C (these may be read off the best fit line on the graph, but would not be as accurate as actually testing it).
