As the volume of hydrogen peroxide increases, the rate of reaction would increase. This is because there are more molecules of H2O2, which would increase the chances of the catalase colliding with a H2O2 molecule. In turn, there would be a higher number of successful collisions between the catalase molecules and the hydrogen peroxide molecules.
The air pressure will affect the rate of reaction as well. The higher the air pressure the more pressure the two substances will be under. The molecules will move faster, which will result in faster breakdown of the H2O2.
As catalase in an enzyme, it will have an optimum pH to work in. Therefore, varying the pH of the solution will affect the breakdown of hydrogen peroxide. At the optimum pH, breakdown of H2O2 will be quite fast, but when the pH changes to either higher or lower than the optimum temperature, the rate of reaction will drop.
Prediction:
As the concentration of the substrate decreases, I think that the rate of the breakdown of hydrogen peroxide will become slower. I think that when the concentration of the hydrogen peroxide halves, I think the rate of reaction will half as well. This is because when the concentration of H2O2 halves, the number of molecules of H2O2 will halve as well, which in turn will halve the rate of reaction. This prediction is based on the results of the preliminary experiment, where the concentration of the substrate, along with other variables, were tested.
Hypothesis:
This prediction is likely to be correct. I know this as enzymes all behave in a specific manor. As the concentration of hydrogen peroxide increases, the speed of its breakdown will increase also. This is because there will be more molecules of H2O2 for the active site of the enzyme to latch onto and break down. One idea about enzyme activity is that enzymes are configured such that only one type of substrate molecule can be broken down in its active site. The shape of its active site is complimentary to the shape of a substrate, therefore it can break it down.
Another idea about enzyme activity is the induced fit theory. This theory states that the active site of the enzyme is NOT identical to the shape of the substrate, but is in fact very similar. It states that the active site is flexible and allows for small changes in shape, which allows the enzyme to be broken down even though it is not exactly the same as the active site.
Method:
To find out how the rate of reaction changes with various concentrations of hydrogen peroxide, the following equipment will be used – a water bath, a collection syringe, a hothman’s clip, a boiling tube, a 1cm3 syringe, a 2 cm3 syringe, a stop watch, a stand and clamp and a delivery tube. Yeast will be used as a source of catalase.
Dilution Table of H2O2 and H2O.
H2O2 H2O
20 1.0 0.0
16 0.8 0.2
12 0.6 0.4
8 0.4 0.6
4 0.2 0.8
0 0.0 1.0
This dilution series will produce 1cm3 of a diluted H2O2 concentration
- First the equipment was set up as in the diagram.
- 2 cm3 of catalase solution was set up in the boiling tube.
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A 1 cm3 syringe was used to get exactly 1cm3 H2O2.
- The hydrogen peroxide was introduced to the solution the syringe and the stop clock was started.
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The O2 given off as the hydrogen peroxide broke down was collected in the test tube.
- When the experiment had been running for 10 seconds, the volume of gas collected was recorded.
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The equipment was reset so a repeat could be carried out for an average. Three results will be obtained from each value to obtain more reliability, as more reading = greater accuracy. Under time constraints, three results for each concentration of H2O2 is a good number of results.
From the data obtained from this experiment a graph would be plotted, with the concentration of H2O2 plotted on the X-axis and the rate of reaction plotted on the Y-axis. In this case, the rate of reaction is going to be volume of O2 collected per minute.
When we measured the volume of O2 we took the reading from the bottom of the meniscus, and we took the reading at eye level as well.
To ensure that the experiment is carried out as fairly and as accurately as is possible, all other potential variables must be identified and steps must be taken to ensure that they are kept the same, or as close as can be possible in a laboratory. Variables that must not be altered include:
Temperature,
Concentration of catalase,
Volume of catalase,
Volume of hydrogen peroxide,
Pressure,
pH.
To keep every other variable the same, a value needs to be decided for each of them. The reaction will be carried out at room temperature, (approximately
21 c) as this will not change significantly during the course of the experiment. This will be the best temperature to carry out the investigation at, as during the pre – testing at higher temperature than room temperature the reaction is to fast to accurately measure. Also, if we were to carry the experiment out at a temperature above room temperature, we would need to keep that constant and it would be impractical to do so. The volume of the catalase will be easy to keep constant, we are using 2cm3 of catalase and this will be measured using a 2cm3 syringe. A 2cm3 syringe will be used to measure it as the smaller the equipment used, the more accurate the measurement is. The volume of the hydrogen peroxide will be kept at 1cm3, and that will be measured using a 1cm3 syringe for greater accuracy. The investigation will be carried out at a pressure of one atmosphere, which will be the only pressure possible in the laboratory.
Justification of Method:
- From the pre-testing it was determined that this is the appropriate equipment to be used. A gas syringe was deemed inappropriate as the pre-testing showed that the volume of gas collected from the experiment would not be enough to register on the scale, so a normal syringe with a hothman’s clip was used instead. It was also determined that 6 readings would give an appropriate number of results to base a graph on.
- The equipment was set up like this for a number of reasons. From the pre-testing, it was discovered that this was the best way to carry out the investigation, and the easiest way to gain the results.
- The pre-testing has shown that this is an appropriate amount of enzyme to use in the experiment.
- A 1cm3 syringe is the most appropriate sized syringe to use to obtain 1cm3 of hydrogen peroxide as it minimises the chances of misreading the results.
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The pre-testing has proven that introducing the H2O2 to the enzyme in this way is the safest and most reliable way of doing so.
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- The rate of reaction is the most suitable data to plot a graph with, so it must be worked out using data gathered from the experiment. This was done by multiplying the result by 6 and finding out how much gas would be collected per minute!
- The equipment needed to be reset after each experiment so that another value could be obtained from the equipment.
The results that were obtained from the pre-testing have led to the conclusion that the best temperature to carry out the experiment at is room temperature. This is because at temperatures higher than room temperature, the experiment has to be carried out in a heated water bath, and this is very hard to keep at a constant temperature. Also, at high temperatures, the reaction is very rapid. It produces a lot of oxygen very quickly and the bong is forced of the top of the test tube by the pressure, rendering the reading invalid.
Risk Assessment:
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H2O2 is corrosive and it can cause burns
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If H2O2 got into the eyes it could cause blindness. Eye protection must be worn at all times because of this.
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If H2O2 gets into the eyes, they must be washed thoroughly with a lot of water for 10 minutes. Medical attention must also be seeked.
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If H2O2 gets on the skin, the area must be washed thoroughly with water for 10 minutes.
- Enzymes are irritants.
- All enzymes are potential allergens.
- Both the catalase and the hydrogen peroxide should be handled to minimise skin contact or inhalation.
- If catalase gets spilt onto clothes or into the eye, a lot of water must be used to remove it.
When the temperature is raised, I think that that the rate of reaction will increase. The Q10 value states that enzymes controlled reactions double in speed if the temperature is raised by 10c, so I think that if the temperature is raised by 10c the rate of reaction will double.
I think that as the concentration of catalase increases, the rate of reaction will increase to a point. I think this because there will be more enzyme molecules available for the substrate molecules to collide with, so therefore there will be more successful collisions between the substrate and enzyme which results in more of the product being produced. The same will also happen if the volume of the enzyme increases.
The volume and concentration of the substrate will also affect the reaction in the same way. The higher the concentration of the substrate, the more molecules there will be to collide with the enzyme. This will increase the overall speed of the reaction. The higher the volume of substrate, the more molecules there will be, so the faster the reaction will occur.
As the pressure is increased, I think the reaction will increase in speed. This will be because the substrate and enzyme molecules will be have more force acting on them pushing them closer together, which would in turn create more collisions between them.
Results:
Concentration of O2 produced per 10s (cm ) volume/minute
H2O2. (vol’s) 1 2 3 Average
20 16.0 14.5 15.0 15.2 91.2
16 11.0 10.0 11.0 10.6 63.6
12 7.5 8.5 8.0 8.0 48.0
08 4.0 4.5 5.0 4.5 27.0
04 1.5 1.5 2.0 1.6 9.6
0 0.0 0.0 0.0 0.0 0.0
Analysis:
As the concentration of the H2O2 increases, the more oxygen is collected in the same amount of time. At the concentration of 4 volumes, only 9.6 cm of oxygen is collected in a minute, but at 8 volumes the rate of reaction had increased and 27 cm of oxygen was collected in a minute. This can be explained using the Lock and Key hypothesis. This explains how the enzyme breaks down the substrate. The enzyme (in this case catalase) is the lock and the substrate (hydrogen peroxide) is the key. The substrate fits into the active site of the enzyme and is broken down into the products, water and oxygen. As the concentration of hydrogen peroxide is increased, the more molecules there are for the enzyme to break down. This increases the number of successful collisions between molecules of the enzyme and substrate which in turn increases the speed of the reaction.
Evaluation:
The results that were obtained in this experiment were quite accurate. The data that was obtained was quite accurate except for the value for 20 volumes. This result was higher than was expected, but this could be due to a number of reasons. The volume of the either the substrate or the enzyme may have been slightly over measured. The result of this would have been that the rate of breakdown of hydrogen peroxide would have stayed faster for slightly longer, increasing the volume of oxygen collected. At the same time, the delivery tube may have been removed slightly after 10 seconds. This would have led to more oxygen being collected. This error would then have been exaggerated further, as when the graph was plotted the volume of the gas was taken as cm / per minute. To get this value the result had to be multiplied by six, so the error would have increased by a factor of 6.
If this experiment was to be carried out again, I would measure more concentrations of hydrogen peroxide. Instead of measuring 20, 16, 12, 8, 4 and 0 volumes, I would instead measure 20, 18, 16, 14, 12, 10, 8, 6, 4, 2, and 0 volumes.
However, the results obtained from the experiment prove that the concentration of the Hydrogen Peroxide does affect the rate of its breakdown.
The experiment itself was carried out in such a way it was possible to obtain the most reliable results. The stop clock was started as the hydrogen peroxide was introduced to the catalase, and after 10 seconds, the test tube was removed from the delivery tube.
