- Place exactly 0.5gms of yeast into a conical flask.
- Pour 10cm³ of hydrogen peroxide into a conical flask with yeast.
- The amount of gas collected in the syringe will be recorded at 5 second intervals to 50 seconds, so that there are 10 all together.
- Repeat this 3 times.
- Repeat all steps again for the five concentrations described below.
Diagram of Set-up:
I have decided to repeat each experiment 4 times in order to obtain more accurate results. By repeating the experiments, I can ensure that there are no anomalies or outstanding results that will affect my overall conclusion for the investigation.
In order to avoid anomalies, I must ensure;
- Hydrogen Peroxide Solution is measured out accurately.
- Make sure that all of the solutions and yeast is reacted together.
- That the gas syringe is free flowing and in full working order.
- Make sure that the bung is attached securely onto the conical flask once the yeast has been deposited into the conical flask.
Once the results are collected and analysed in the form of graphs etc, I will be able to conclude whether or not it supports my original hypothesis. The graphs will enable me to find correlations and trends and I will therefore be able to conclude the investigation.
Fair Test:
In order to ensure my experiment is a fair test I will have to ensure other impact posing variables are kept constant, i.e., so that concentration of the hydrogen peroxide is the only variable in the experiment.
In order to draw a fair, accurate conclusion I will have to:
- Use only 0.5gms of yeast for every test.
- Use a total of 10cm³ solution for all experiments.
- Use the same type of yeast size throughout the experiments.
- Use the same equipment throughout the experiment.
I will need to keep the above, constant throughout the experiment because they can potentially affect the final results.
If the amount of yeast was more for one experiment then there will be more catalase enzymes in the reaction which will therefore mean the reaction is quicker and as far as results are concerned, there will be more gas given off in a certain time period.
If there is more hydrogen peroxide concentration in a n experiment than there should be, this will mean that the collision rate is increased and will therefore increase the reaction rate and the amount of gas given off in a certain time.
It is also very important to maintain a constant temperature the experiment is carried out in to ensure that the enzyme is not affected. If the temperature is increased nearer to 30 degrees Celsius then the enzyme activity will increase and will give off more gas in a certain time. In order to prevent this happening, I will set-up my experiment in an area where it is away from direct sunlight, window or radiator.
Accuracy:
-I will take appropriate level of accuracy for all measurements for each item. The mass of yeast will be taken to 0.01 grams with the total being 0.50 grams each time.
-Liquid measurements (solutions) will be measured to the nearest cm³ as this is the most accurate possible to judge yourself, as opposed to a digital device such as weighing scale.
-Time readings will be taken to the nearest second, despite the stop clock providing a more accurate figure, this is because I will not be able to stop the clock during the experiment as this will delay further readings.
-The accuracy of the gas syringe will be to the nearest cm³.
-If the experiment is carried out as shown in the method, bearing in mind the points on the fair test section, the results should be highly accurate. However, there is possibilities that one of the processes goes wrong which is why I am repeating the experiment 3 times so that any anomalous results can be spotted and so an accurate mean of the results can be calculated.
Following these guidelines will help me draw a more valid conclusion at the end of the experiment.
Preliminary Experiment:
I carried out a trial experiment prior to the actual investigation with the same aim involved. I did this trial experiment in order to find out what volumes and amounts to use as well as other points in order to achieve the most accurate results possible. It also helped me produce my hypothesis for the investigation as well as ensuring I employ the best possible method.
In the trial experiment I initially used 2 grams of yeast, however the reaction between the catalase enzymes and hydrogen peroxide was far too rapid to accurately take down readings at the appropriate time intervals. I therefore decided to use 1 gram to reduce the overall reaction rate and this proved effective.
Trial Experiment Results: Volume of Oxygen Given off (cm³)
The results clearly show that there is a problem within the method. When the concentration of hydrogen peroxide was at 100% the rate of reaction was so high, that 100cm³ of oxygen was given off in less than 20 seconds. This would not allow me to make a fair conclusion as a direct comparison between concentrations is not possible to identify if they finish at different times. I decided, in order to amend this problem I had to decrease the rate of reaction by reducing the amount of enzymes, by which I would have to reduce the amount of yeast to 0.5gms.
Despite, the immense speed of the 100% concentration experiment, I was able to find out that my hypothesis was generally correct. However, there is every possibility that these results were ‘anomalous’ and that the final experiment would show different results.
Results:
Once the experiment was carried out as described in the method shown previously, the following results were obtained.
Experiment 1: Volume of Gas Given Off (cm³)
Experiment 2: Volume of Gas Given Off (cm³)
Experiment 2: Volume of Gas Given Off (cm³)
Mean Results: Volume of Gas Given Off (cm³)
Analysis:
From the graph showing the averages for each concentration of Hydrogen peroxide, I can say that the curves show a positive correlation indicating that there is a link between rate of reaction and concentration.
However, there are many anomalous results which do not lie on the ‘best curve’ which indicates that the practical was not accurate enough to draw more positive, valid conclusion.
Conclusion:
By looking at the graph, it is quite apparent that as the concentration of hydrogen peroxide is increased, the rate of oxygen formed increases; ultimately indicating that the reaction rate is quicker. Or, as the concentration of hydrogen peroxide is reduced, the rate of reaction is decreased as well.
The catalase enzyme (yeast) activity increases as the hydrogen peroxide does, because there is simply more to react with; because the catalase enzymes will not react with water.
The reason as to why the rate of reaction gradually decreases in the experiment, for all concentrations, is because there is less hydrogen peroxide molecules left and it is therefore harder for them to make contact with the enzymes as there will be more larger water molecules in the same solution coupled with oxygen molecules being given off. This is why there is a larger gap between each curve at the end than at the start of each line.
Therefore, my findings support my hypothesis in that as the concentration increases, the rate of enzyme activity will also increase producing oxygen. The overall correlation is strong.
Evaluation:
I felt that the experiment was a good, simple way of carrying out the experiment with very few complications or flaws. By carrying out the method, I was able to record 3 sets of results and plot a graph showing this visually and mainly, to draw a fair valid conclusion.
The conclusion supported my hypothesis which also supported the scientific theories talked about previously.
I thought that the main problem with the experiment was the recordings and the securing.
Because times had to be recorded every five seconds, I found that I was far too rushed to comfortably note down accurate readings. It would therefore be sensible to take measurements over 10 second periods if I were to repeat the experiment.
Therefore, the accuracy of readings were inevitably inaccurate and in order to achieve much more accurate results using the same method, I would need to repeat the experiments several times over. There were no anomalous results in my experiment and my results were not very accurate stressing that, the experiment should really be repeated many more times to find a more accurate mean.
I would also recommend that all experiments were carried out on the same day to avoid changes in temperature and other technical issues such as using the same equipment etc..
The main improvement that could be made to this experiment, in order to obtain far more accurate results would be to use a dividing conical flask, instead of simply adding the yeast and the scurrying to get the bung on as quickly as possible. This would make the experiment a much fairer test and would generally provide more efficient, accurate results to draw a more valid conclusion upon.
