Concentration of catalase (yeast). – If the concentration of catalase is high then there will be more catalase molecules which means they can get round the breaking down of the H2O2 quicker. This means the rate of oxygen produced will be higher if the concentration of catalase is high, and be low if the concentration was low.
Volumes of H2O2. – if you have a large volume of H2O2 and you mix it with catalase then the break down rate will be faster than a small volume. This is because if there is a larger volume then there are more H2O2 molecules around and available for the catalase to breakdown. This means the catalase will find a match fast and easily so the breakdown rate will be faster and the rate o oxygen produced will increase.
Method
To test out how the concentration of Hydrogen Peroxide affects the rate of reaction first set up the apparatus and prepare the different concentrations of Hydrogen peroxide as below:
Apparatus.
- 6 boiling tubes. – so the reactions can take place in them.
- Hydrogen peroxide – to react and give of oxygen and water.(concentration is 10vol.)
- Catalase in yeast suspension – To speed up the reaction.(concentration is 5%).
- Delivery tube – to transport any gas produced from the reaction.
- Distilled water – to lower the concentration of hydrogen peroxide.
- 1cm3 syringe – to squirt the catalase in with the hydrogen peroxide quickly.
- 10cm3 measuring cylinder. – to collect any oxygen from the delivery tube and then measure the amount of oxygen in it.
- 500cm3 beaker – to hold the water in so the gas stays separate from anything else.
- Tap water – to keep the gas produced separate and allow itself to be displaced by the gas (in the measuring cylinder)
Tube Volume of H2O2 (CM3) Volume of water (CM3) H2O2conc. (vol.)
1 1.0 0 10
2 0.8 0.2 8
3 0.6 0.4 6
4 0.4 0.6 4
5 0.2 0.8 2
6 0 1.0 0
- Prepare the concentrations and set up the apparatus as shown in the diagram above.
- Take tube 1 and connect it up to everything (making sure it is air tight)
- With a stopwatch ready start it as soon as you push the syringe to release the 1cm3 of catalase.
- Release the catalase and start timing. Look at the measuring cylinder and record how much the water has gone down at 5, 10, 15, 20, and 25, 30 seconds.
- Write down your results.
- Now repeat steps 1 – 5 but instead of taking tube 1, take tube 2. When you’ve done that take tubes 3,4,5 and 6 and do the same for them.
- Now repeat the method again, this is to check that your results are similar each time.
Safety.
For Safety Reasons Please…
· Wear goggles to protect because your eyes because H2O2 is an irritant at the concentration used.
· Clear desk / work area of any unnecessary materials.
· Hydrogen peroxide can be irritant to skin be careful. So wash your skin if any gets on it. It can also dye your skin (bleach it)
· If any spillages of any liquid, have a cloth to clean it up, could cause wet floor surfaces, and in the event of this accidents may occur.
I am measuring the rate of oxygen being produced at 5, 10, 15, 20, 25, 30 seconds when the reaction is taking place. I will measure this by observing the measuring cylinder and seeing the water level on it. This will tell me the rate of the oxygen produced.
I know that the gas given off is oxygen because I tested it with a burning splint and the flame grew bigger and flared up, then went back to normal. I will ensure my results are reliable by taking the readings three times each; I do this to check I don’t have any anomalous results. And to calculate an average. (please note that if results are taken twice then do it on the same day and with the same apparatus. Do this because if you do it on different days then your results will be different because of the temperature of the room etc.)
Fair Test
To make my investigation a fair test, I’ll use one variable, and I’ll repeat it three times to gain an average and compare the results to see if they are similar. The water and hydrogen peroxide will be measured in a clean, measuring cylinder every time I require it. This is so that, the right volume is applied so that none of my overall results are faulty in anyway. I’ll be using a digital stopwatch, so that each experiment has the same amount of time to react. I shall always be checking that the stopper on the test tube is always firmly on tight because of the gas pressure, and any other equipment that could be faulty. Keep the same apparatus, because apparatus differs for instance on test tube may be more air tight than the other. You also need to do on the same day and the same room to avoid different results because of temperature. You also have to make sure you stir the yeast every time you suck it up with the syringe without fail.
Temperature – This is a factor in my investigation because if the temperature is cold then the particles will move slower than if the temperature is warm. The reason for this is because when it is warm the particles move a bit faster there for giving a faster rate of reaction. I can’t actually control the temperature in the room with the equipment I am using because it isn’t very advanced. But this won’t effect the fairness of my investigation because I will do all my investigation on the same day with the same temperatures.
Accuracy – Accuracy is very important to be careful of, because if something is slightly inaccurate e.g. when you prepare the tubes you put in slightly too much water, then it will effect your results. You also have to ensure you stir the catalase every time you suck it up with the syringe, to make sure the concentration is the same each time.
Awareness of the recorder – This is also important because if you aren’t feeling alert then you will obtain delayed and inaccurate results. Because we don’t have the most advanced equipment we have to rely on ourselves to as aware and accurate as possible. I will control this by making sure I am fully alert before I carry out my investigation.
Non-faulty apparatus – If the apparatus is just slightly faulty then it will effect your investigation. E.g. if your apparatus isn’t airtight then some oxygen that is produced will escape and this will affect your results. I can control this factor by checking everything over at the beginning.
The measurements I will make are the volume (in cm3) of oxygen collected in the measuring cylinder.
Tube Volume of H2O2 (CM3) Volume of water (CM3) conc.
1 1.0 0 10 vol.
2 0.8 0.2 8 vol.
3 0.6 0.4 6 vol.
4 0.4 0.6 4 vol.
5 0.2 0.8 2 vol.
6 0 1.0 0 vol.
The values are suitable and will make my results more reliable because as I found out in my preliminary work if you have a large volume of liquid in the test tube then the rate of oxygen produced is too quick to get any good results from. The measuring cylinder gets filled in under 5 seconds. They are also good because they are all easy to deal with. It isn’t complicated to work them out because it works in a pattern.
My measurements won’t be extremely accurate because if you are sucking a liquid up with a syringe then you won’t be able to get exactly the measurement you want because it is very difficult. My observations won’t be amazingly accurate either because it is hard to see the exact level of the water when the reaction is taking place because sometimes the level is falling rapidly. But I will make my results as accurate as I can with these limitations, by using an accurate stop watch and measuring oxygen given off to nearest 0.5cm3.
Preliminary work
I had to do quite a lot of preliminary work to gather evidence to support my investigation. Also, to ensure my investigation is done in the easiest and most efficient way possible. In my preliminary work I found that you should always stir the catalase because if you don’t the reaction is slower because some of the yeast cells settle to the bottom. I also found that it is best to only have a small volume in the test tube, this is because if you have too much then the rate of oxygen produced is too high and is difficult to record because the measuring tube is filled up in under 5 seconds. In my preliminary work I also tested the gas that was being produced with a burning and the burning splint flared up and the flame grew and then died down. This is the test for oxygen and the test came out positive. I also found out that you can obtain more accurate results if you use distilled water instead of tap water, this is because distilled water is completely neutral and won’t affect anything, especially PH apart from the concentration of the hydrogen peroxide when it’s added. You should always keep pushing down the stopper on the test tube to ensure it is airtight. I used smaller volumes of H2O2 so I could obtain easier results. Here are some preliminary results to show that large volumes of H2O2 get broken down too quickly to read any results off them.
These results are using my altered method.
These trial results have helped me finalise my plan because I feel very confident about taking the readings now for when I do the real thing. They have also helped because I am half way to proving my prediction is correct. They have helped me finalise my plan because I can see now that they back up my scientific knowledge. The trial results went well so I will be using a similar format for when I do the real thing.
Results
All my repeat readings were similar and I got one anomalous result and I have put a circle around it. Other than that I didn’t get any anomalous results. Because the results are similar each time I can assume they are reliable and I can draw a conclusion from them.
Here my results are the same as the previous page but on this one I tired out 4 vol. For 30 seconds again and this time I didn’t obtain an anomalous result.
Volume of o2 collected (cm3) in a given time (secs).
graph
Analysis.
I have taken the reading of volume of oxygen produced at 10 seconds for each concentration of H2O2 and multiplied It by 6 to give an initial reaction rate in cm3 per minute for each concentration. See below.
graph
Conclusion.
“Changing the concentration of H2O2 altered the rate of reaction between the catalase and its substrate.” I know this because the rate of oxygen produced in my investigation changed as I altered the concentration of H2O2.
“At 10 vol. Concentration the rate was 54 cm3 oxygen released per minute. At 8 vol. Concentration The rate was 24 cm3 oxygen released per minute.
Here I can see a relationship between them, as the concentration decreases by 20% the rate approximately halves.
“At 2 vol. Concentration the rate was 6 cm3 per minute. At 4 vol. Concentration the rate was 9 cm3 per minute.”
This roughly backs up my relationship as well. Although it is not exactly double every time it roughly is.
This relationship happens because as the H2O2 is more concentrated the rate of reaction is quicker. It happens because at low concentrations there aren’t enough H2O2 molecules to react with all the catalase and there are spare catalase molecules with nothing to breakdown. The reason for this is because with a higher concentration there are more molecules for the catalase to react with, so they can react at a faster rate. The active site is trying to find the H2O2 to lock with so when they collide they can lock together and react.
I think the rate would keep increasing until it would get to a stage where the catalase was breaking down as fast as it ever could because there has to be a stage where the catalase can’t breakdown any faster because all the catalase molecules are breaking down the H2O2 molecules as fast as t can and won’t be able to break down any faster unless a variable is changed. In the enzymes globular structure, one or more polypeptide chains twist and fold, bringing together a small number of amino acids to form the active site, which is where the reaction takes place. Enzyme and substrate fail to bind if their shapes do not match exactly. This ensures that the enzyme does not participate in the wrong reaction. The enzyme itself is unaffected by the reaction. When the products have been released, the enzyme is ready to bind with a new substrate. So if there is more molecules the catalase can get through the reaction quicker.
I used some information from Encarta above.
Evaluation.
We chose to measure the oxygen collection method instead of the height of the froth because collecting the oxygen is a lot more accurate than measuring the height of froth. The reason measuring the height of froth isn’t a very good idea is because some bubbles burst, froth is made of yeast, oxygen and water and there are different sizes of bubbles.
I think my results were as good as they could be considering my limitations. Some things made it difficult to gain very accurate results, such as: Only being able to use your eyes to measure the volume of oxygen produced, by doing this you are quite likely to be 0.2cm3 out or so. Also Timing because my partner and I had to tell each other when 5 seconds had passed and then the other person would say the volume of oxygen that had been produced. By the time we had told each other time had passed so in fact it wasn’t actually always dead on 5 or 10 seconds when we took the reading. Also the method we used puts you under a bit of pressure because you are trying to collect results quickly so you are bound to get something a bit inaccurate.
To help me keep accurate results I had to remember to always wash out my boiling tubes when I had used them, to stir the catalase to get the yeast evenly
distributed, leave the syringe in the bung and to take special care that when I sucked up a substance with a syringe I made it as accurate as I possibly could and when I pushed the liquid out the syringe I made sure I pushed it down all the way.
My repeats were actually very close apart from one anomalous result, so I can say that I think my results are very reliable.
I did get one anomalous result and there are a couple of reasons for why that could be: I could have forgotten to clean out the boiling tube and caused there to be a faster reaction than there should be, or I didn’t make up the concentrations quickly this time. All the results for this tube are quicker than the other 2 at the same concentration. Maybe the concentration was higher than I thought.
I don’t think my investigation was very fair, ideally I would have liked to have taken all of my results on the same day to avoid temperature changes but I couldn’t. Other than that I can’t recall anything that would have made my investigation unfair.
To make my results more reliable I could have done the test even more times to gain a larger average and also get better and better at doing the investigation fairly. That way you could seek out more anomalous results and gain more accurate results. To extend the investigation I could do it with different people and maybe compare my results to other peoples. I could try different batches of yeast to see if it really did make a difference. To improve my method I could use much more sophisticated equipment. Such as: a way to carry out the investigation where you can keep a constant temperature. E.g. A room that is temperature controlled. Computer equipment that records the volume of oxygen produced when it s exactly the required time. Advanced equipment that would ensure I put every last drop in when I am doing the investigation.
For accuracy I tried to be as accurate as possible, however there were some things I didn’t control. The results might not have been as accurate as they could have been when timing. I only used a stop clock, which relied on my reaction, to stop the clock. Everyone’s reaction times are different so is not particularly the most accurate way of timing. Also you had to decide where you would start timing, when you first tart pushing the syringe or when you have finished. All these things make difference but I think I got past the problem because I ensured that I did the same for each one.
If I were to do this experiment again I would take into account all the problems I have noticed here. I will also try to be more accurate. However despite these criticisms I do feel that my conclusion is reliable, as I only had two anomalous results, and it does support my prediction.