To start the reaction, the catalase was injected into the conical flask containing the mixture of hydrogen peroxide and water. Once the solutions had made contact I immediately started the stopwatch, the reaction was left for 30 seconds so many experiments could be completed in the time given, once the time had been reached on the stopwatch the burette was moved to stop anymore oxygen from entering the burette to avoid anomalous results. After the 30 seconds the amount of water displaced in the burette by the reaction was observed and recorded from the meniscus point in the burette to ensure the accuracy of the data every test was repeated three times to ensure more reliable results.
After each experiment the conical flask was washed and dried with distilled water and paper towels to make sure there weren’t any reactants left behind to alter my data. This precaution insured that there weren’t any substances from pervious experiments. After all the experiments were completed, the data collected was recorded and used to make a table, graphs and calculate the rate of reaction. From the data I was able to draw a conclusion what happened during this investigation.
Results
This table shows the volume of oxygen produced the average rate of reaction between catalase and different concentrations of hydrogen peroxide for 30 seconds.
Graphs
This graph shows the average volume of oxygen produced for each concentration.
This graph shows the rate of reaction with the concentration of hydrogen peroxide.
Analysis
My results indicate that the rate of reaction between the catalase and the hydrogen peroxide increases as the concentration is increased; this can be calculated by dividing the average amount of oxygen released by the time. My graph shows that there is a relationship between the volume of oxygen collected in 30 seconds and the concentration of hydrogen peroxide, more oxygen is being produced per second with 6% than 5% the data collected in my table and on the graphs clearly indicates that there is positive correlation between the concentration and the volume of oxygen produced. By changing the percentage concentration of the hydrogen peroxide I am changing the number of substrates present in the reaction. The volume of oxygen produced indicates the rate of reaction in that the faster the oxygen is produced the faster the rate of reaction, the concentration had a significant effect on the rate of reaction, From my background knowledge I already know that when an enzyme is present in a reaction the rate of reaction increases anyway. for example the average volume of oxygen at 6% concentration the highest concentration is 0.52 (cm3/sec), however at 3% concentration the average is 0.4 (cm3/sec).this proves that the number of substrates present affect the amount of oxygen released, I can tell this because the volume of oxygen released increases due to the increased probability of successful collisions with a hydrogen peroxide molecule increases producing more water and oxygen molecules.
my results not only show the trends between the concentration and the rate of reaction, they also show the volume of oxygen collected is not directly proportional to the concentration of hydrogen peroxide as the difference between each concentration when the percentage concentration is increased is not constant, for example, the difference in the volume of oxygen collected between 2% and 3% is 1.2cm3 of oxygen, whereas between 4% and 5% concentration the difference in the volume of oxygen collected is 0.6cm3. with all the precautions taken one anomaly occurred in my data, the table indicates that the rate of reaction of 4% concentration is lower then it should be, there third retest at 4% concentration showed a very abnormal result, this result is far lower then the first two tests I believe this was caused by an error in observing, the oxygen displacing the water in the burette many have been stopped to early at the particular point in time, fortunately this anomaly only occurred once so it only had a mild affect on one of my concentrations. I am confident with my results however there were places where my results could have been affected by my accuracy and by other unforeseen variables that I cannot control. As I can see from my graph, my results are not that accurate otherwise they would be in a perfect straight line therefore there must have been variables outside of the experiment which were affecting the experiments to either speed it up or slow it down the rate of reaction.
Evaluation
while experimenting there where several limitations in the apparatus and technique that were used I will explain how my results are affected by this error, what the error is caused by and how it can be improved, and what affect this improvement will haven on my results. One major way I could have improved my results would be the number of tests completed, only three test were done for each concentration performing more tests would have given me even more information which could have been used to calculate more accurate averages and therefore a more accurate graph and line of best fit. I was unable to complete more than three tests because I was limited in time and I only managed to get my three repeats done in time. If I had got more results during the time of the experiment then this would have allowed me to calculate the rates of reaction for each concentration of hydrogen peroxide by drawing a graph and calculating the gradient for each concentration. This would have helped to show that the rate of reaction increases as the percentage of hydrogen peroxide concentration increases. However this would not have helped to give me more accurate results as the volume of oxygen collected at the end of thirty seconds would still be the same as my graph in this coursework. The delivery tubing in my experiment should have been tested to see if there were any leaks in it by letting water flow through it when it was set up like in the experiment. If there were leaks then I could have either covered these with a thick coating of Vaseline or got a new delivery system. If there were a leak in the tubing that was used it is probable that some oxygen escaped and was not measured in the burette. This would directly affect my results and would make them inaccurate, if there were no leaks then my results would not have been affected by this means.
When using the measuring cylinders and syringes I used ones which were supplied. I should have adjusted the size of the measuring cylinder to the volume of hydrogen peroxide that I was collecting so that my percentage error would be reduced. I should have used a 10cm3 measuring cylinder for the 6% hydrogen peroxide concentration and then a 5cm3 measuring cylinder for the rest of the concentrations. You can calculate percentage error using the formula:
Accuracy X 100%
Volume
This means that the 100cm3 measuring cylinder has a percentage error of ±25% as it could only read it to ±0.25cm3 . I could only read the 10 cm3 syringe to ±0.1 therefore the percentage error is ±10%.I had used a 5cm3 syringe to measure some of the hydrogen peroxide the syringe would have been able to read these to ±0.025cm3 which is only a ±2.5% percentage error, which very accurate whereas using the measuring would cause a higher chance of error. A major source of error is the sample preparation and maintaining the yeast and hydrogen peroxide as they can decay over time. It would have been better if the hydrogen peroxide and the yeast were kept in the water bath at all times and keep the hydrogen peroxide out of the sunlight as it can be decomposed by UV light. The yeast used in the experiment may have also had some impurities in it which may have affected my results. I could not start the timer and squirt the hydrogen peroxide at the same time so I worked with a partner, the problem with this squirting the hydrogen peroxide, it takes time to press all the hydrogen peroxide into the flask therefore the timing was a bit inaccurate. That limitation may have meant that the rate of reaction was not recorded at precisely the time that the reaction occurred, Because of this limitation my data may fail to show the correct rate of reaction because the reactions are happening late, the effect this limitation has on my data is my rate of reaction are lower then they should be, because some of the reaction is continuing after the 30 seconds, this would cause my graphs not to reflect the true rate of reaction. It would have been better if I had a syringe that could press all the hydrogen peroxide with less force so the timing with the stop clock would be more accurate this may have improved my results slightly.
Seeing as rates of reaction are so sensitive to temperature during the experiment I found that water bath used to keep the temperature equal began to fluctuate as the experiment progressed causing changes in temperature of reactants to decrease, this would have lowered the rate of reaction as the particles would have less kinetic energy.
