Potato and Osmosis Investigation
Introduction
Potatoes contain the enzyme Catalyse which catalysis the breakdown of Hydrogen Peroxide (H2O2) into oxygen and water, the equation for this is:
2H2O2 2H2O + O2
Catalyse
Hydrogen Peroxide water + oxygen
Catalyse
The breakdown of the H2O2 is caused by the enzyme catalyse breaking it down using the lock and key theory. The lock and key theory is where, (in this experiment), the catalyse molecule has an 'active site' which part of a hydrogen peroxide molecule fits into (i.e. lock and key theory). Once a Hydrogen Peroxide molecule has met a catalyse molecule, chemical bonds form between them and then water molecules attack the bonds and weaken them. The hydrogen molecule then breaks up into water and oxygen. The oxygen given off is what we are going to measure in this experiment to calculate the rate of reaction (speed at which the reaction takes place) under certain conditions (in this experiment it will be temperature).
This diagram is the enzyme breaking down the substrate, using the lock and key theory. This is what happens when the particles collide with each other (see paragraph below for information on how they collide).
There are four different conditions in which the rate of reaction can speed up or slow down, and they are based on the idea of the collision theory. The collision theory is the theory that when particles collide with each other they will react. The more force they collide with the more likely they are to react instead of just bouncing off each other. The rate of reaction depends on how often and how hard the particles react, the more often the particles collide and react with each other, the faster the rate of reaction. There are four different conditions that can effect the rate of reaction by increasing, the chances of the particles colliding.
The different conditions that can effect the rate of reaction are as follows:
Concentration
The stronger the concentration the faster the rate of reaction because there is more particles to be broken down, so more chance that they collide.
Surface Area
The surface area of the particles can effect the rate of reaction because with a larger surface area the particles have more chance of colliding with each other.
Catalyst
A catalyst increases the number of collisions by giving the particles a surface to stick to where they can collide and react with each other.
Temperature
The temperature is the one I will be measuring throughout this experiment and it can increase the number of collisions. When the temperature is increased the particles will move quicker. If their moving quicker, it means there be more collisions. But the temperature can only be increased up to a certain point where the rate of reaction will start to decrease. This is because of the active site of the enzyme particles starting to disfigure in high temperatures, so the substrate cannot fit the active site and just bounces of, so the particles don't react. Also if the temperature is too low the particles can slow down and not collide with each other that often meaning that there is a slower rate of reaction.
The concentration of the mixtures and the surface area of the particles both need to be controlled in this experiment for the experiment to be accurate.
Aim
I am going to find out, at which temperature will the rate of reaction be the quickest.
Hypothesis
The higher the temperature, the slower the rate of reaction.
Prediction
I think the rate of reaction will be the quickest at around 40?C because from the introduction I can conclude that it works best around this temperature. If it is higher than this temperature then the active site will become distorted, and if the temperature is lower the particles will not collide as often.
Preliminary Experiment
In this preliminary experiment, I am trying to find out how much H2O2 to use in the main investigation. I am going to do this by varying the amount of H2O2 and seeing which amount works best and ...
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Prediction
I think the rate of reaction will be the quickest at around 40?C because from the introduction I can conclude that it works best around this temperature. If it is higher than this temperature then the active site will become distorted, and if the temperature is lower the particles will not collide as often.
Preliminary Experiment
In this preliminary experiment, I am trying to find out how much H2O2 to use in the main investigation. I am going to do this by varying the amount of H2O2 and seeing which amount works best and makes the rate of reaction faster. H2O2 is going to be the only variant in this preliminary because that is what I am testing. I have to make sure that the amount of washing up liquid and the temperature will stay the same in each test so it makes this preliminary investigation a fair test.
Apparatus
3 test tubes
Test tube rack
2 syringes
Over 9ml of H2O2
Over 3ml of washing up liquid
Water bath heated to 40?C
Stopwatch
Ruler
A Potato
cm diameter potato borer
Scalpel
Goggles
Method
. Collect apparatus
2. Heat water bath to 40?C (check with thermometer)
3. Pour 2ml of H2O2 into one of the test tubes and place in water bath
4. Bore out a piece of potato using a 1cm diameter borer, and cut them with a scalpel to 1cm long (they must all be exactly 1cm)
5. Put 1ml of washing up liquid into a syringe
6. Add the piece of potato into the test tube in the water bath, and then straight afterwards add the washing up liquid and start the stopwatch
7. When the stopwatch reaches 1 minute, pick up the test tube and measure the height of the foam (including the washing up liquid) and record it in mm.
8. Repeat this every minute up to and including the tenth minute.
9. Repeat this procedure for the other two test tubes, but use 3ml of H2O2 in one and 4ml of H2O2 in the other. Record all results.
Results
A Graph to show the rate of reaction of the breakdown of H2O2 at different amounts by catalyse at 40?C
Time/min
Height of foam (including washing up liquid)/mm
2ml
3ml
4ml
9
0
7
2
2
4
1
3
6
20
3
4
8
24
9
5
21
27
21
6
23
30
23
7
23
30
24
8
24
31
25
9
25
31
25
0
25
31
26
Average Height of foam (minus height of washing up liquid)/mm
9.6
24.8
9.4
Average rate of reaction/mm/min (to 1 decimal place)
.96
2.48
.94
Preliminary Experiment Conclusion
The rate of reaction was the quickest with 3ml of H2O2 in the test tube rather than 2ml or 4ml. It did not work well with 2ml of H2O2 because the H2O2 did not cover the whole potato so there wouldn't be as much catalyse to breakdown the H2O2 molecules because part of the potato is out of the H2O2. I did not know why 4ml was not the quickest as I expected it to be the quickest because there would be more H2O2 molecules for the catalyse to break down, so there would be more collisions, but it was not the quickest. In my main investigation I want to use the amount of H2O2 which has the rate of reaction the quickest. I want this because a larger height of foam is easier to measure than a smaller height. A larger height is easier to measure than a smaller height because the measurements will be further apart from each other, this makes it a lot easier because it is hard measuring a small height of foam with a ruler, as you can't be that accurate. This means I will use 3ml of H2O2 because the rate of reaction was quickest with 3ml.
Main Investigation
Apparatus
Water bath
Ice
Tub (to contain the ice)
Thermometer
Test tubes
Washing up liquid
Hydrogen Peroxide
Test tube rack
Test tube holder
Stopwatch
Goggles
Ruler
Syringes
cm potato borer
Potatoes
Scalpel
Diagram
Fair Test
* All equipment must be clean and dry before using it, as it would not be a fair test if other chemicals or extra water were added to the hydrogen peroxide during the experiment.
* All bits of potato must be exactly 1cm long and 1cm in diameter
* A separate syringe is used for the washing up liquid and the hydrogen peroxide
* Temperature is correct in the water bath when adding the hydrogen peroxide
* H2O2 and washing up liquid must be measured accurately
* Temperature is checked in H2O2 before adding washing up liquid
Safety
* Goggles must be worn when handling hydrogen peroxide to stop any going in eyes
* If hydrogen peroxide is spilt on hands wash off with water to stop irritation
* When using the 80?C water bath, use test tube holders to pick up testy tubes to avoid burns
* When using a scalpel to cut potato, do not touch blade and be wary of it when cutting to avoid cutting yourself
* Cut potato on a flat surface and not in hand to avoid cuts
Method
. Collect apparatus and set up as shown in diagram
2. With the 1cm borer, bore out some potato and cut 3 pieces with a scalpel to 1cm long. Each piece will have a surface area of 4.17cm2.
3. Add 3ml of H2O2 to each test tube using a syringe.
4. Place one test tube into a 40?C water bath using a test tube holder to hold it in there. Make sure the water is 40?C or as close as it can get.
5. Get the stopwatch ready and put 1ml of washing up liquid into a syringe.
6. Add a potato piece to the hydrogen peroxide and straight after, add the washing up liquid and start the stopwatch at the same time.
7. After one minute, pick up the test tube and measure the height of the foam (including the washing up liquid) with the ruler and record the results in mm.
8. Repeat after every minute until the tenth minute (include the tenth minute) and record results.
9. Do this in the 40?C water bath, 3 times using different test tubes. You do this to find an average.
0. Repeat the whole of the above procedure for 60?C, 80?C (both in a water bath), 20?C (about room temperature, so don't use water bath or ice) and 0?C (do this by putting the ice in the tub, and putting the test tube in with the ice. Try to get it as near to 0?C as possible, as it will not reach exactly 0?C). Record all results.
Results
Rate of reaction of the breakdown of H2O2, by catalyse in potatoes, over 10 minutes at 0?C
Time/
Min
Height of foam (including washing up liquid)/mm
2
3
4
Average (minus height of washing up liquid)
/mm**
Rate of reaction/
mm/min (to 2 decimal places)
9
5
20
9
5.0
5.0
2
4
25
27
21
9.7
9.9
3
5
45*
27
23
20.7
6.9
4
6
30
29
25
22.3
5.6
5
8
28
30
28
24.3
4.9
6
9
40
29
28
24.3
4.1
7
22
40
29
29
25.7
3.7
8
23
40
30
32
27.3
3.4
9
23
43
28
33
27.0
3.0
0
23
41
31
35
28.7
2.9
Average = 5.9
*Miss measured (maybe) so repeated
**Excluding 2nd set of results
Rate of reaction of the breakdown of H2O2, by catalyse in potatoes, over 10 minutes at 20?C
Time/
Min
Height of foam (including washing up liquid)/mm
2
3
Average (minus height of washing up liquid)
/mm
Rate of reaction/
mm/min (to 2 decimal places)
6
6
5
8
8
2
3
3
24
5.7
7.9
3
20
8
29
21.3
7.1
4
26
22
30
25
6.3
5
30
24
36
29
5.8
6
33
28
39
32.3
5.3
7
35
30
41
34.3
4.9
8
38
34
42
37
4.6
9
40
35
43
38.3
4.3
0
40
37
45
39.7
4.0
Average = 5.8
Rate of reaction of the breakdown of H2O2, by catalyse in potatoes, over 10 minutes at 40?C
Time/
Min
Height of foam (including washing up liquid)/mm
2
3
Average (minus height of washing up liquid)
/mm
Rate of reaction/
mm/min (to 2 decimal places)
7
9
Scrapped because test tube cracked and not enough time to repeat.
7
7
2
25
20
21.5
0.8
3
27
23
24
8
4
30
24
26
6.5
5
31
24
26.5
5.3
6
30
24
26
4.3
7
30
24
26
3.7
8
29
23
25
3.1
9
28
22
25
2.8
0
27
21
23
2.3
Average = 6.4
Rate of reaction of the breakdown of H2O2, by catalyse in potatoes, over 10 minutes at 60?C
Time/
Min
Height of foam (including washing up liquid)/mm
2
3
Average (minus height of washing up liquid)
/mm
Rate of reaction/
mm/min (to 2 decimal places)
9
8
2
8.7
8.7
2
9
9
2
9
4.5
3
8
8
0
7.7
.0
4
7
8
9
7
.8
5
6
7
8
6
.2
6
6
6
7
5.3
0.9
7
6
6
6
5
0.7
8
6
5
6
4.7
0.6
9
5
5
5
4
0.4
0
5
5
5
4
0.4
Average = 2.0
Rate of reaction of the breakdown of H2O2, by catalyse in potatoes, over 10 minutes at 75?C
Time/
Min
Height of foam (including washing up liquid)/mm
2
3
Average (minus height of washing up liquid)
/mm
Rate of reaction/
mm/min (to 2 decimal places)
7
0
8
7.3
7.3
2
6
8
7
6
3
3
6
7
6
5.3
.8
4
7
6
6
5.3
.3
5
5
5
5
4
0.8
6
4
5
4
3.3
0.6
7
4
5
4
3.3
0.5
8
4
4
4
3
0.4
9
4
4
4
3
0.3
0
4
3
4
2.7
0.3
Average = 1.6
Conclusion
The final graph on the last page shows that with the temperature at 40?C the rate of reaction was the fastest because it was 6.4mm/min. Then it dramatically dropped from there to 60?C (rate of reaction 2.0mm/min) then to 75?C where it was the slowest rate of reaction at 1.6mm/min. The 0?C (5.9mm/min) and 20?C (5.8mm/min) had a slightly slower rate of reaction than 40?C did. In all the experiments the rate of reaction gradually decreased over 10 minutes which the graph before the final graph shows. This is because the particles are being used up, so their as many reacting as time goes on.
The graph shows that the rate of reaction did decreased as time went on and this was because as the temperature increased the particles received more energy so they moved faster meaning that they collide more often, increasing the number of reactions. But this happened up to a certain point, which was at 40?C. After 40?C the rate of reaction started to drop quite rapidly, this is because of the active sites of the enzymes (the catalyse) start to disfigure after you reach a certain temperature. If they disfigure it means that the substrate (the H2O2) can not fit the active site, so the lock and key theory can not be performed meaning there is no reaction. This is why the reaction gets so much slower after 40?C. On the 0?C and 20?C experiments the rate of reaction was slower than the 40?C reaction. This is because, if the experiment is at a colder temperature, the particles do not get as much energy as in a warmer temperature experiment like 40?C, so they do not collide as often causing a slower reaction.
There were some anomalous results, which have been shown in the table. These anomalous results are on the second set of results on the 0?C experiment. These results are most likely to be caused by human error and poor measuring. Also on the 40?C experiment the test tube cracked and filled up with water so I couldn't complete the experiment.
The rate of reaction is quickest at 40?C but second quickest was 0?C with a rate of reaction at 5.9mm/min instead of 20?C being the second quickest at 5.8mm/min which is surprising as I would have expected 20?C to be the second quickest.
Evaluation
My prediction was proved because the rate of reaction did work best around 40?C and also my hypothesis was also proved as when the temperature increased after a certain point the rate of reaction did slow down. This is because of the active site of the enzyme catalyse getting disfigured in a high temperatures, this means that the substrate H2O2, can not fit the active site so the lock and key theory can not be performed.
The experiment was actually not accurate because there is no way of knowing how much catalyse was in each piece of potato so it was unfair. There were also some anomalous results like the 2nd set of results at 0?C, but those were caused by human error. Also the 3rd set of results at 40?C was scrapped because the test tube was cracked and it filled up with water, we would have repeated it but there was not enough time.
The results on the 0?C experiment and the 20?C experiment were both expected to be lower than 40?C and they were, but 0?C was faster than 20?C, which was not expected. This was not expected because the colder the experiment is done at, the slower the particles should move. So that means that the rate of reaction should be slower for a colder experiment but it was not. Possible reasons for this are that there was more catalyse in the piece of potato in the 0?C experiment than the 20?C experiment, causing the 0?C experiment to have a rate of reaction just as fast.
If the experiment was done again, it could be improved in several different ways, like the catalyse being measured in the potatoes some how, to ensure that the amount of catalyse is equal in each experiment to make it a fair test. It could also be improved if I had more time to complete it and the cracked test tube result could be repeated. Also there should have been a lot more care in taking the results to avoid measuring poorly and maybe double check the measurement each time so there are no anomalous results. This experiment probably wasn't the most accurate ways of measuring the rate of reaction, however with more time the experiment could be improved by taking more results to be more accurate and doing the experiment at more temperatures. You could also take more results to find a more accurate average. Some other methods of measuring the rate of reaction is to measure the amount of oxygen given off by attaching a tube going to a syringe so when oxygen is given off the syringe will move back. Then you measure the distance it has gone back. I think this is a better way of measuring it because it is more accurate than just measuring the bubbles because some oxygen from the experiment can escape through the bubbles so your not measuring all the oxygen, so it is not a fair test.
To further investigate the rate of reaction you could try it with different enzymes, particles and quantities of everything used to see which ones work best and to get more accurate results.
