Investigating the Breakdown of Hydrogen Peroxide To Oxygen and Water By Catalase Enzyme.
Investigating the breakdown of hydrogen peroxide to oxygen and water by catalase enzyme.
AIM
To investigate the how increasing the mass of potato [and therefore the amount of catalase enzyme] effects the volume of oxygen produced. There are a few variables:
* The concentration of hydrogen peroxide.
* The volume hydrogen peroxide.
* The amount of catalase which is in the cubes of potato.
* The surface area of the potato.
* The temperature at which the reaction takes place.
These are variables because:
* If you increase the concentration of hydrogen peroxide, there are more H2O2 molecules per cm3. Therefore there is a greater oxygen content, so more oxygen will be produced.
* If you increase the volume of hydrogen peroxide, then more oxygen will be produced by complete decomposition because there are more O2 molecules in the solution.
* Increasing the amount of catalase means that the reaction will go faster. The yield of oxygen will not change [because the number of O2 molecules is not changed], but more oxygen will be produced in a give time because the rate of decomposition is greater.
* If you increase the surface area of the potato, then it will have the effect of increasing the rate of reaction as a larger amount of catalase is presented to the H2O2 molecules in solution. More oxygen will be produced in a given time but the total volume of oxygen produced after increasing surface area does not change total decomposition.
* The higher the temperature the more energy the molecules have, so the there is a higher the percentage of successful collisions.
The more catalase you have the faster the rate of reaction is.
Catalase is a biological catalyst. Without the presence of catalase in this reaction, hydrogen peroxide would still decompose to oxygen and water though far more slowly. Catalase speeds up the rate of this reaction, but remains unchanged itself. Its structure is the same at the end of the reaction as it is at the beginning.
* Enzyme +Substrate Enzyme substrate complex Products.
* Catalase +hydrogen peroxide Water + oxygen
APPARATUS USED FOR EXPERIMENTATION
* Digital timer- for accurately recording amount of time taken.
* 2x boiling tubes
* Water tank
* Delivery tube
* Rubber bung-oxygen produced only passes into the test tube; therefore none escapes.
* 1x scalpel-to cut potato cubes
* 1x ruler -to measure size of potato cubes.
REACTANTS USED IN EXPERIMENTATION
* Beaker of hydrogen peroxide
* Beaker of de-ionised water-to dilute hydrogen peroxide[equal volumes of each]
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* Enzyme +Substrate Enzyme substrate complex Products.
* Catalase +hydrogen peroxide Water + oxygen
APPARATUS USED FOR EXPERIMENTATION
* Digital timer- for accurately recording amount of time taken.
* 2x boiling tubes
* Water tank
* Delivery tube
* Rubber bung-oxygen produced only passes into the test tube; therefore none escapes.
* 1x scalpel-to cut potato cubes
* 1x ruler -to measure size of potato cubes.
REACTANTS USED IN EXPERIMENTATION
* Beaker of hydrogen peroxide
* Beaker of de-ionised water-to dilute hydrogen peroxide[equal volumes of each]
* 1x potato
Method
* Cut up potato into 1cm3 cubes using a scalpel.
* Fill test tube with 5cm3 hydrogen peroxide and 5cm3 de-ionised water
* Insert delivery tube into rubber bung
* Fill another test tube and a water tank full of water
* Put rubber bung [with delivery tube] into test tube and insert delivery tube into container of water
* Cover the end of the delivery tube with the test tube filled with water, while submerged in water to prevent the entry of air, which would provide inaccurate results.
* Put desired number of potato cubes into test tube and quickly replace bung to prevent loss of oxygen.
* Start the timer the moment the bung has been inserted into the test tube.
* When the test tube is empty of water due to displacement by oxygen [and therefore full of oxygen], the timer is stopped and the number of seconds recorded.
SAFETY
* Care taken when using scalpel to cut potato cubes.
* Care taken when handling hydrogen peroxide to avoid spillages and eye splashes.
ACCURACY
* All potato cubes are cut from the same potato so that the amount of catalase is more constant; making results more accurate as the catalase constant[and so behaviour in experimentation ]could vary between potatoes
* The same apparatus is used in each experiment
* The same method is employed for each experiment.
* A digital timer is used to accurately record time taken.
* The timer is stopped immediately when the test tube is full of oxygen.
* The second test tube has no air bubbles in it prior to experimentation.
* There is only one variable: number of potato cubes.
* The volume of hydrogen peroxidase is constant:5cm3
* The concentration of hydrogen peroxidase is constant
* The surface area of blocks used is accurately measured to 1cm3, so that rate of reaction is more constant for each experiment.
PREDICTION
As the number of potato cubes increases, so does the mass of potato and therefore amount of catalase. Catalase is an enzyme [a biological catalyst], which speeds up the decomposition of hydrogen peroxide to water and oxygen. As the rate of reaction is speeded up, more oxygen will be produced in a given time [because the rate is increasing].
Therefore, I predict that as the number of potato cubes increases, the amount of time it takes for the test tube of water to be displaced will decrease, as more oxygen is produced in a given time. I predict that my graph of results will look like this:
I also predict that as number of potato cubes increases, so will the rate of reaction, because more catalase molecules will be presented to the same number of hydrogen peroxide molecules (as both concentration and volume of hydrogen peroxide are constant).
Table of results
Number of cubes
Result
No.1
Time taken to collect 60cm3 of oxygen
ResultNo.2
Result No.3
Rate of reaction no.1
Rate of reaction no. 2
Rate of reaction no. 3
36
40
35
.7
.5
.7
2
30
30
33
2
2
.3
3
9
20
9
3.2
3
3.2
4
8
0
0
7.3
6
6
5
5
7
5
2
8.6
2
(Each cube 1cm3)
Rate of reaction
(1cm3 of oxygen per minute)
CONCLUSION
My results show that as the number of potato cubes increases, the time taken to fill the test tube with oxygen decreases. This is exactly what I predicted. The reason why this happens is that as the number of potato cubes increases, so does the amount of catalase present. Catalase is a biological catalyst (enzyme), which speeds up the decomposition of hydrogen peroxide to water and oxygen. If there is more catalyst, then the rate of reaction will be speeded up even more, so more oxygen is produced in a given time. The test tube is filled with oxygen more quickly, so the time taken to fill a test tube decreases as number of potato cubes increases. The relationship shown by this graph is indirect proportion.
The time taken to fill a test tube when one potato cube was used was 36 seconds. The time taken when 5 cubes were used was 5 seconds.
The line shows a slight curve, which indicates that the time taken is changing because of another reason. A fast rate of reaction relies on successful collisions. In order for a collision to be successful there must be sufficient activation energy so that particles collide with enough force to react. This is heat energy. When the H2O2 bonds are broken, energy is used (this part of the reaction is endothermic). When bonds are formed, heat is given out. In this decomposition reaction, the heat given out from the reaction causes a further increase in the rate of reaction; which is seen as a curve on the graph. This is an indirect consequence of the increase in catalase.
My second graph shows how rate of reaction changes with number of potatoes used. I worked out the rate by using the following equation:
Rate = Amount [Amount of oxygen = 60cm3]
Time
As I predicted, as number of potato cubes used increases, so does the rate of reaction, due to the increases in amount of catalase. The relationship shown by this graph is of direct proportion. The line does not go through the origin. If there were no cubes, there would be no reaction, but there would still be a small amount of air in the test tube because air is pushed out of the test tube by the pressure of the bung being pushed into the
Tube.
EVALUATION
I am pleased with my results, as they are consistent with my predictions and with the scientific knowledge on which they were based. This is a suggestion that my results are fairly accurate, and therefore that the method and equipment use were well suited to the experiment; as accurate results were produced. I do not assume that each of my results are to 100% accuracy of their true value, but I have no anomalous results [although human error must be taken into consideration.]
To improve the accuracy of my results I would ask a friend to start and stop the timer when the bung was inserted and the test tube was full. The only difficulty I found with this method was that it was impossible to both insert the bung and start the timer in the same instant. Therefore the time figures would be very slightly inaccurate in each case because I started the timer shortly after having inserted the bung. However, I do not think my results and conclusions are less valid because of this. I do not have any anomalous results, I can tell this by my graph. This reflects well on the way I conducted my experiment.
If I were to continue the investigation I would vary the volume or concentration of the hydrogen peroxide and measure the total volume of oxygen produced. This would enable me to see how the number of oxygen molecules changes with either volume or concentration, as opposed to the how rate effects the amount of oxygen produced in a given time. I would be investigating how much oxygen is produced as opposed to the time it takes to be produced. I think that as volume/concentration increase, so would the total volume of oxygen produced. I could also vary the temperature, the PH, the volume of substrate etc. These would all have an effect on the rate of reaction.
