Plan
The variable that I’m going to change is the concentration of hydrogen peroxide (H O ). I am using hydrogen peroxide because the concentration is easy to manipulate. There will be five concentrations of hydrogen peroxide that I will use: 20%, 40%, 60%, 80% and 100%. The 100% of hydrogen peroxide is the equivalent of 16 vol.
I will measure the rate of reaction by recording how much oxygen has replaced the water in a measuring cylinder after thirty seconds. I will be doing this for each of the different concentrations of the hydrogen peroxide and record the results in centimetres cubed (volume).
My source of catalase enzyme will be yeast (2%) as it’s homogeneous, easy to prepare and simple to measure accurately. Homogenous means it’s the same throughout and won’t change in anyway whilst the experiment is taking place. In preliminary work I found that by using mushroom, yeast, liver and celery that the yeast gave a good range of results this is why I am using it in my experiment.
Fair Test
- To carry out a fair test I will use 3cm of yeast for each of the different concentrations. If I changed the amount of yeast each time my results wouldn’t be accurate as all would have reacted more or less than another, which is not the method I am investigating.
- I will use 5cm of the hydrogen peroxide concentrations. If I changed the amount of hydrogen peroxide each time then my results, again, wouldn’t be accurate as all would have reacted differently.
- I will also keep the concentrations of the substrate (20%, 40%, 60%, 80%, 100%) and catalase (2% yeast) the same. If any of the two should change in the experiments my results would be made up of anomalous results.
- I will keep the same temperature (room temperature) throughout as an increase of heat could create more kinetic energy in the particles affecting the rate of reaction and the amount of oxygen gas released. If the temperature decreased the particles would gradually loose their kinetic energy and react less or even not at all.
- Whilst the experiment is taking place it is important that I keep the exact amount of time for each of the reactions (30 seconds) because if one has more time than another then there is a high chance that the oxygen gas would have more time to be released.
- Finally, I will change the water in the plastic tub after every experiment as the heat caused by the reaction will heat up the water in the tub causing an intervention in the temperature of the test tube. Which in turn could speed up the reaction between the hydrogen peroxide and yeast, interfering with my results.
To ensure my results are reliable I will test the same percentage of hydrogen peroxide three times then take an average from my results. As hydrogen peroxide is a powerful oxidising agent and can be potentially damaging to cells, I will wear safety glasses and work safely and sensibly throughout the experiment.
After I have completed the experiment I will use my data to produce graphs to see if there is any correlations or patterns according to the amount of gas released and the percentage of hydrogen peroxide in my results.
Prediction
I predict that as the concentration of the substrate increases, the rate of reaction will speed up because the more particles there are the higher the chance of collision. When the substrate and catalase particles collide with each other they form enzyme substrate complexes this then breaks down the hydrogen peroxide into water and oxygen. So as the concentration increases more enzymes substrate complexes are formed but at a faster rate. This is justified by the diagram below:
Method
- Fill a plastic tub with water then place a measuring cylinder filled with water into it standing it upright.
- Connect a delivery tube leading from the inside of the measuring cylinder to the outside and attach a bung.
- Next, take 5cm of the 100% of hydrogen of peroxide and put it into a test tube.
- Add 3cm of yeast to the hydrogen peroxide then quickly place the tube with the bung attached to it over the test tube to stop the oxygen being released into the air.
- Time thirty seconds on a stop clock until recording the volume of oxygen.
- Repeat this method three times and for all of the concentrations, noting the volume of gas that has replaced the water in the measuring tube.
Gradually the water in the measuring tube should be replaced with oxygen from the yeast and the hydrogen peroxide reaction.
Equipment
- 500cm Water
- 1 Plastic tub
- Hydrogen Peroxide-20%, 40%, 60%, 80% and 100% concentrations (5cm of each concentration for each test)
- Yeast (2%)-3cm for each of the tests
- 50 ml Measuring cylinder
- Delivery tube
- 5 ml Syringe
- Stop Clock
Diagram
Results
As you can see, I started my experiments from 20% hydrogen peroxide this is because if I started with the 100% hydrogen peroxide then some of its concentration could have contaminated the lower concentrations making them a higher concentration than expected, making the test unfair.
The volume of oxygen increases as the concentration increases because more enzyme substrate complexes are formed, when the catalase breaks down the hydrogen peroxide it creates water and releases oxygen. As more of theses enzyme substrate complexes are formed more oxygen therefore is released. These facts come back to my prediction thus justifying it.
From my results I can see only one anomalous result this is when I did the second test on the 40% of hydrogen peroxide. As a result of this, I can prove why I repeated the tests for each of the concentrations, without doing so my results could be unreliable as they would show errors in my experimenting and not in the actual result of the reaction.
Evaluation
I think the quality of my results are fairly accurate but considerable changes should happen if I was to act upon this experiment again this is so that I can be sure my results are a hundred percent reliable. For instance, I should have checked the room temperature before each test so that there weren’t any fluctuations and made sure the test tube with the hydrogen peroxide and yeast in was at the same temperature for each of the tests. I could also have done five tests instead of three to have made my results even more accurate then recorded them precisely up to the nearest millimetre cubed.
I could also do some further work to add additional relevant evidence to this experiment. One way I thought of was to heat the test tubes the hydrogen peroxide and yeast are placed in to get an increased reaction. Another way would be change the concentrations of the hydrogen peroxide from going up in twenties to going up in fives to increase the accuracy of my results.
Concluding this experiment I would say that concentration in a reaction is extremely important in what result is wanted or to be tested.