diagram here
Preliminary Experiment:
Method:
First of all I will fill the water bath and place it on the bench.
Then I will fill the burette with 50cm cubed of water and invert it, so the holed end is in the water. I will make sure no water has escaped into the water bath.
Then I will run a delivery tube from the inverted end of the burette and attach it to the top of the bung that will go on the conical flask.
I will fill the conical flask with 50cm cubed of Yeast solution and place the bung on it.
Using the syringe I will extract and hold 5cm cubed of Hydrogen Peroxide. I will place the syringe in the hole on top of the bung that has been designated for it.
I will lastly inject the Hydrogen Peroxide into the Yeast and start the Stopclock, and measure the amount of time it takes for the oxygen given off by the reaction to displace all the water that is in the burette.
Before I do the real experiment, I will do a practice run called a Preliminary to make sure I am doing what I will need to be with good enough accuracy. This will also allow me to set the constants required in the experiment and get some experience in how to carry out the procedure. With the 3 results at least I have a good chance of a good average and fairly reliable results. Also my preliminary will point out any potential problems in the experiment when I do the proper version.
Fair Test:
There are several factors in both the Preliminary and the actual AT1 that could strongly influence the results and give false results. I need to do each concentration at least 3 times to iron out any possible false readings.
The accuracy of the concentration dilution can affect the readings in a substantial way. Even if the percentage is as little as half a percent out, it could sway the result and add say 5 seconds to the time. I will need to be as accurate as possible when I dilute the Yeast to make sure it is as close to the specified percentage as possible. This will reduce the chance of a false reading and give me an overall more accurate reading.
Also the diluted concentrations of Hydrogen Peroxide will be an affecting factor. As with the Yeast I will need to keep it as close to the specified concentrations as I can. Volumes of the chemicals will also be a factor because if I use to much yeast and too little Hydrogen Peroxide for example, this will also influence the results.
Prediction:
Using the information I have gathered I am able to make a prediction of what may happen in this experiment. I hypothesise that as the level of Yeast decreases, there will be less Catalase to work on the Hydrogen Peroxide, thus taking longer to complete the break down of the given amount.
Results:
Mistakes:
On the whole I was pleased without this experiment but there are I suspect a few mistakes. One that caught my eye was 4% Yeast with 50cm3 of water. As with the other experiments, there is a steady increase in the time it takes between each reaction, but the gap between 50cm3 and 40cm3 is about 9.5 seconds instead of the previous 2-3 seconds. There may be many explanations for this but the one i suspect the most is that too much water was present in the Burette. This may be because i neglected making sure it was the correct amount and just filled it right up. Another that I thought strange was 3% Yeast with 30cm3. How could the reaction take .38 of a second to do an extra 10cm? I can only conclude that yet again I have neglected to make sure the Burette is at the right water level. In this case it could have been substantially less than what it should have been or I may even have done the same test twice.
Averages:
Based upon my averages I can see that 2% Yeast appears to be wrong. It took allot longer than the other tests, almost double the time of 3% Yeast. I would theorise that the concentration of Hydrogen Peroxide may have been too high, but I didn’t actually do anything with the supply of H2O2 so this rules out that theory.
Rate of Reaction:
By dividing the time by the volume of chemicals used I can work out the rate of reaction. I can compare the rate of reaction in this preliminary to the real experiment and hopefully decide which is the most commanding variable. The rate of reaction for this experiment is:
Looking at these rates of reaction i can assume that 2% Yeast was not done properly. The gaps in time between the other 3 experiments are all a few milliseconds but 2% Yeast is more than 2 seconds ahead.
Possible causes of Anomalous Readings:
One factor that I highly suspect is that I did not have the correct amount of Water in the Burette. This would make it take longer, thus giving a strange reading. Another possibility could be Oxygen leaking away. Some of the Oxygen may have escaped from the bung or the delivery tube. Making sure the bung was tightly fitted or selotaping the delivery tube to the top of the bung to let no Oxygen out may have been a good thing to do. I would also suspect the status of the Yeast might have been influential. If it was not evenly mixed i.e. most of the Catalse was at the bottom like a silt, then it would have taken longer for the H2O2 to reach it and initiate the reaction. Stirring the Yeast to make sure it was evenly mixed could have improved the accuracy of the results.
What have I learnt from the Preliminary?
The preliminary taught me that I need to be as accurate as I can with every quantity I have to use, including making sure there is not too much water in the burette because this could falsify the result. I have also learnt to be careful when handling the Hydrogen Peroxide so I do not accidentally get it in my eyes or ingest it. Also I now know it would be best to take at least three if not four readings, then if one of them is out of place, I can still obtain a workable average from the remaining three.
Proper Experiment:
Method:
I will do exactly the same as i did with the Preliminary, but i will change the variables. Variables: I will need to alter the concentration of Hydrogen Peroxide from 20 vol. (which is what I will start off with) to 16, 12, 8 and finally 4 vol. I will do each of these percentages 3 times to give me an average and to allow for a fair test. For example if I come out with 1 result being 25 seconds, another at 23.5 seconds and the last 1 at 30.75 seconds it might be said that the 3rd one is out of place and inaccurate.
Fair Test:
There are several factors in both the Preliminary and the actual AT1 that could strongly influence the results and give false results. I need to do each concentration at least 3 times to iron out any possible false readings.
The accuracy of the concentration dilution can affect the readings in a substantial way. Even if the percentage is as little as half a percent out, it could sway the result and add say 5 seconds to the time. I will need to be as accurate as possible when I dilute the Hydrogen Peroxide to make sure it is as close to the specified molarity as possible. This will reduce the chance of a false reading and give me an overall more accurate reading.
Also the diluted concentrations of Yeast (5%) will be an affecting factor. As with the Hydrogen Peroxide I will need to keep it as close to the specified concentrations as I can. Volumes of the chemicals will also be a factor because if I use to much yeast and too little Hydrogen Peroxide for example, this will also influence the results. In addition to this, I will carry out all my tests at room temperature, trying to make sure the temperatures do not change. I will also measure the temperatures of the solutions before I mix them. If they are different temperatures, then it may quicken/ slow the reaction and affect my results.
In this experiment, I will be measuring how long it takes to accumulate 20cm3 of Oxygen gas.
Prediction:
The lower the H2O2 concentration, the slower the reaction. This may be because there will be less Hydrogen Peroxide to react with, which means it will take longer to give off the required amount of Oxygen. This is because there will be less collision between the enzyme and the Hydrogen Peroxide, so less interaction interactions between the enzyme’s active site and the H2O2.
Results for the proper experiment:
Mistakes:
I suspect that a couple of the results in this table are incorrect. One suspect is test 2 of 4 vol. H2O2. This reaction is more than twice as fast as the other 2 in its group. There could be many reasons for this miss-hap. I suspect the H2O2 may not have been diluted too much or there was not enough yeast present.
Another that caught my eye was test 3 of 12 vol. H2O2. It is only a minor difference, but the other 2 are in within 3 seconds of each other, but this one is at least 4 seconds off the 1st result. This just shows how precise and accurate this experiment needs to be.
On the other hand I was pleased with the 8 vol. and 20 vol. experiments. they were all within a few seconds of each other and will give a reliable average.
Averages:
Based upon these averages I can see that 4 vol. appeared to have taken far too long compared to all the other results. This could be for many reasons but I suspect the 1st and 3rd results from this group were too slow. The other in the same column as these 2 is less but the aspect of 2 of them being slow compared to 1 quick one may imply that both the slow ones were inaccurate. Surely the speed of reaction would have dropped more uniformly like in the previous columns where the gap is not as great.
Rate of reaction:
By dividing the volume of gas collected by the time it took, I can work out the rate of reaction.
Using these rates of reaction I can deduce what may or may not have gone wrong with my experiment. I was particularly displeased with 4 vol. H2O2. It is very out of place compared to the rest of the results and I can only assume that the times were wrong on the 1st and 3rd of these tests. These 2 were more than half the 2nd test result so I am not sure whether they are correct because they are the majority, or if it was the 2nd test that was right because the jump in time seems more logical and explainable.
Graph Analysis:
The above graph has shown me that as the concentration increases, so does the time it takes to react.
4 vol.= 0.32
20 vol.=1.18 -
0.86 over 16 volumes.
0.86 divided by 16 vol gives an increase of 0.05 per each vol.
This proves my theory. I can explain this rise in rate of reaction because there will be more H2O2 for the Catalase to react with. This means there will be more collision between the enzme and H2O2 so the rate of reaction will increase. My graph shows a straight line of increases. However I cannot explain why it curves at the top, beacuse surely it would keep going straight. The only possible explanation for this I can make is that I performed the experiments inaccurately and made a few mistakes.
Evaluation:
I think the results were workable and fairly reasonable, and they did what they were supposed to do by allowing me to prove my theory.
One possible reason for the apparent wrongness of 4 vol. H2O2 I suspect is that the concentration was not as accurate as it could have been. I may have used too much or even too little water, or the Yeast may have been too weak on the 1st and 3rd try, but as it should have been on the 2nd attempt. I do not think Oxygen Leakage (as mentioned in the preliminary) could be a major factor but once again I must suspect the accuracy of the amount of water in the burette.
