I think the best method for my investigation is the gas syringe method, as it is the most reliable and accurate, and not messy.
I will need to change one factor to affect the rate of the reaction. The key factors are;
- temperature at which the reaction takes place
- amount of catalase compared to the amount of hydrogen peroxide
- pH of the solution
- concentration of hydrogen peroxide
I am going to change the amount of hydrogen peroxide. I am doing this to see if the enzyme can still break down the substrate if more is added, and at the same rate.
I will need to be safety conscious and therefore wear safety glasses, and tie my hair back out of the way of the liquids. I will need to be careful and concentrate on my own investigation and be particularly cautious when pouring hydrogen peroxide. I will make it a fair test by keeping everything the same, for example, the amount of catalase, and I will only alter my key factor, the amount of hydrogen peroxide. I am going to make 8 observations per investigation, ranging from 2cm3 of hydrogen peroxide to 9cm3 of hydrogen peroxide. I am going to keep the yeast solution at 2cm3 throughout, as I think this is an appropriate amount, not too high or too low. I will repeat my investigation twice to ensure I have accurate results as well as carrying out a pilot test to check my amounts of yeast and hydrogen peroxide are fine to use and not too high or low. Therefore I will be carrying out one pilot test and three final investigations. This will also ensure my method works properly and is accurate, and will allow me to make any necessary modifications.
Prediction
I predict that the more substrate added, the faster the rate of the reaction, because of the ‘collision theory’. In order for a reaction to occur, the particles involved must collide, and these collisions must be successful. Not all collisions are successful though. The more collisions, the more likely they are to be successful. By increasing the concentration of substrate in the solution, I am also increasing the number of particles, making collisions more likely. As there are more collisions, they are more likely to be successful so the reaction will happen faster. Therefore, the higher the concentration of substrate in the reaction, the faster the rate of the reaction will be.
Apparatus
1 x test tube
2 x syringes (one for measuring the yeast solution, one for the hydrogen peroxide)
2 x beakers (one for the yeast solution, one for the hydrogen peroxide)
1 x clamp
1 x gas syringe
1 x stop clock
1 x trap (with bungs and delivery tubes)
1 x test tube rack
Yeast solution
Hydrogen peroxide
Method
Set up the apparatus as shown in the diagram. Measure out 2cm cubed of yeast solution into the test tube and the desired amount of hydrogen peroxide, and quickly bung it. Start the stop clock, and after 15 seconds, record the amount of oxygen that has been released, as shown on the gas syringe, into the table. Repeat the recordings after 30 seconds, 45 seconds and one minute also.
To check my method works and produces accurate results, I am going to do a pilot test, using the method stated. If my method is simple and produces accurate results, I will continue with the investigation. If not, I will alter my method and pilot test again until I am satisfied with my method and results.
Pilot Test Results
My results appear to be accurate as the oxygen released increases as the substrate is added. My method was simple to use and I found no fault with it, so I will continue with my investigation.
Obtaining Evidence
Investigation 1
Investigation 2
Investigation 3
Analysis
I have calculated the mean averages for each measurement over the 3 investigations and I have recorded them in the table below. I have plotted these averages on a graph on a separate sheet of graph paper.
Averages Table
My graph (see appendix) shows each curve to follow a pattern of a steep gradient at the beginning of the reaction, followed by a flatter slope as the reaction continues. One anomaly to this pattern is the 9cm3 result, as it has the steep gradient at the beginning, but this steepness continues, and does not flatten out as the other lines appear to do after a while. I think as my results all follow the same pattern, except the one curve, my results are accurate and reliable. I am not sure why this anomaly has occurred, but I think to improve my investigation, I could use more frequent concentration changes such as 2cm3 of hydrogen peroxide, 2.2cm3 of hydrogen peroxide, 2.4cm3 of hydrogen peroxide and so on. This would make the results a lot more reliable, and it would probably be easier to see a reason behind my anomalies as well.
My results fit my prediction, as the steeper the line, the faster the reaction is reacting, so as the lines get steeper as the concentration gets larger, the rate of reaction is getting faster as the concentration increases, so my prediction is correct.
Evaluation
If I was to repeat my investigation, I would take more accurate readings by using more frequent hydrogen peroxide concentration measurements as explained above. Also, using a bigger range of values, e.g. from 0.2cm3 of hydrogen peroxide and measuring every 0.2cm3 up to a higher value e.g. 20cm3 would give me a larger range of measurements to work with, and would ensure more accurate and reliable results. I think my method was reliable as my results, despite the one anomaly, supported my prediction, which was accurate due to my scientific knowledge of the collision theory.
Conclusion
The higher the concentration in a reaction, the faster the reaction rate.
