Diagram
- pH
Each enzyme has an optimum pH at which its active site best fits the substrate. I will have to take this into account.
- Concentration
By increasing the concentration I would expect the rate of reaction to increase as there would be more particles therefore they would collide more per second and increase the rate of reaction.
This is my chosen variable that I will change
The experiment was set up as shown above. Hydrogen peroxide and water concentrations were varied and the gas was collected. I tried the concentrations shown below as by choosing a solution high in concentration of H2O2 and one with a much lower concentration of H2O2 meant I would have the range I was planning to dealing with.
Results were obtained as follows although, these are not precise readings as the results were only meant for giving a rough guideline.
From the preliminary work I decided:
- To use the 20cm2 syringe instead of the 1cm3 or 10cm3 syringes that were also on offer.20cm3 was the volume I wanted to use and this would make it easier to vary the concentration. The reason I wanted a volume of 20cm3 is that the errors of each would be less important that if the values were small and errors made substantial differences.
- I will use minced potato rather than…as the reaction was rapid therefore less time would be spent waiting for the reaction to take place.
- I will use the stop clock provided
- Two minutes was the time I was going to let the reaction go on for until taking my volume of the gas reading. I came to this decision while doing the 100% concentration of hydrogen peroxide. I timed how long it took for about 90 cm3 of gas to be produced. It took just over 2minutes.There would not be quicker reaction than this therefore there wouldn’t be more oxygen produced in 2 minutes.
Prediction
I predict that if I have a higher substrate concentration, then this will cause a higher rate od catalase activity, because there will be more active sites for a reaction to take place. I expect the results of the volume of oxygen produced in a fixed time to be directly proportional to the increase of hydrogen peroxide in the solution.
Apparatus needed for the experiment
Conical flask with bung and tube attached
Graduated Measuring cylinder (100cm2)
Beehive shell
2 troughs
Tap water
Hydrogen peroxide of 100% concentration
Mincer to mince potatoes
Potatoes
Digital Stop clock
Overall and Goggles
20cm3 syringe
Method
- Measure 10g of minced potato, which has been minced in a mincer for 30 seconds and put in a conical flask
- Fill a beaker with the pre-made measured solution of hydrogen peroxide and water. This will need to be done after every different concentration.
- Set up the experiment as shown below:
- Add 20cm3 of the prepared solution in the conical flask using the 20cm3 syringe. Straight after, press the button on the stop clock and let the timing start.
- When the stop clock reads 2mins, note down the volume of gas in the cylinder.
- Repeat this experiment with the same concentration three times. The do the same thing for all the solutions shown in the table below. The reason for the repeats is that any anomalous results can be spotted. We can also look at the reliability of the data depending on how close the repeats are to each other.
Hydrogen peroxide is an irritant. We will be using a 20 Vols hydrogen peroxide, which is considered safe for our use. The 20 Vols hydrogen peroxide, which is considered safe for our use.. The 20 Vols hydrogen peroxide will be known as the 100% solution. I will wear eye protection and overalls to avoid contact with eyes and skin.
Obtaining
ANALYSIS:
Analysis of results: Fig 1 is a free hand graph of the table. From the graph, I am able to back up my theory. I can see when the enzyme is most active. From the graph, I have found out that, as the amount of hydrogen peroxide in the solution decreases, the catalase activity also decreases, as more oxygen gas is given of when there is more hydrogen peroxide in the solution. This is where the greatest number of collisions takes place between the enzyme and the substrate and therefore it has the highest rate of reaction is.
CONCLUDE
The rate was higher at high concentrations of hydrogen peroxide (ie:the reaction was fastest at an enzyme concentration of100%solution) because as there are more substrate molecules, they collide more often and therefore more reactions take place between them. This, in turn, means that the rate increases as more oxygen (O2) is produced. When there was no hydrogen peroxide in the solution no reaction took place.
The results of this investigation are as I predicted in the hypothesis: The reaction will increase with increasing molecules of hydrogen peroxide. However, there are a number of variables that influence the decomposition of hydrogen peroxide in the presence of catalase. Some are named as “Limiting factors”. They are factors that limit the rate of reaction. These include temperature, catalase concentration, and hydrogen peroxide solution. All of these factors are required for an efficient reaction to take place, even when one is freely available the reaction can still be limited by the availability of the others
Although the ranges of hydrogen peroxide concentrations taken were large, the difference in the volume of gas produced between each reading was fairly large. For example, the rate of reaction at a substrate concentration of 40% and 50% had a large difference in volume of oxygen produced
I didn’t include the anomalies in my graph because I thought they would affect the graphs line of best fit. These results may be anomalous because I started the stopwatch too early or too late or I didn’t fill the whole of the measuring cylinder with water or I didn’t push the bung in properly.
EVALUATION:
Although I conducted the experiment as accurately as I could there were many sources of error in the method that I used.
Firstly, to start the experiment I needed to put the Hydrogen Peroxide into the conical flask containing the minced potato, and start the stopwatch straight away. I also think it would have been better if I had used the same potato for the whole experiment but was unable to due to the time restrictions. I had to conduct the experiment over a number of days and could not therefore use the same potato. This is a source of error because the concentration of catalase in the potatoes may have been different which may have produced an inconsistent rate of reaction. This might be why the values I obtained and thought were anomalies did not quite fit the pattern of the graph that I expected. Also as the potato is left over days the catalyse decomposes and therefore the amount of catalyse on one day could be more than the catalyse in the potato on the second or third day.
To do a further experiment I think that I would change the type of potato. As I used minced potato the reaction occurred rapidly. It would be interesting to see the reaction happening over a longer period and see how the increase occurs. I could redo the experiment at a different temperature and see if the pattern still arouse.
The evidence that I obtained is sufficient enough to support the conclusions I have come to. My evidence is reliable, as I have obtained three repeats per concentration that are fairly close together, as the graph shows.
