Keeping the pH levels the same
The Temperature always keeping the elements at 22o
Time – same person timing
If variables were not controlled I would not get accurate results because there would be too many things to measure so it wouldn’t be fair.
Prediction
I predict that the catalase enzyme found in the starch will break down the substrate (Hydrogen Peroxide) quickest when there is 10ml of the starch and It isn’t diluted at all with any water, the enzyme will become denatured if there is more than 10ml of water so molecules of Hydrogen Peroxide won’t be able to fit into it and so they can’t form an enzyme substrate complex and can’t be broken down, so no oxygen or water is created. I predict that the graph for the total oxygen evolved will look like this:
I think this because between A and B the rate of reaction increases the molecules of Hydrogen Peroxide will have more kinetic energy and so there will be more collisions, as they move around the container and hit each other. More enzyme substrate complexes will be formed and so more oxygen and water is formed.
At point B the amount of gas given off is the optimum.
Apparatus:
Before I can begin my investigation I need to get all the apparatus I will need:
¨ Tub the set-up:
¨ Delivery tube
¨ Measuring cylinder
¨ Boiling tube
¨ Stopwatch
¨ Gas syringe
¨ Boss
¨ Clamp stand
.. Clamps
.. Pipette
Boiling Tube
Method:
1) I got together all the apparatus.
2) I then put the bosses and clamps onto the clamp stands
3) Using the pipette I measured out 10ml of starch and Hydrogen Peroxide.
4) I Then I used the clamp stand to hold the gas syeringe.
5). I attached the boiling tube to the other clamp
6) I put the starch into the boiling tube.
7) I added 10ml of Hydrogen Peroxide to the boiling tube.
8) Then I put the bung in the test tube and immediately started the stopwatch.
9) Every ten seconds for 2.5 minutes I recorded how much gas had been made.
I will repeat each test once. Amount of starch I will use is
Preliminary Experiment
Before I started my main investigation I needed to know what a suitable range of water to use and how much Hydrogen peroxide and catalase to use. Here are my results for 10ml H2 O2 + 5ml starch + 5ml water
Here are my results for 7ml H20 + 3ml Starch
From this experiment I decided that I needed to use more starch for a quicker reaction and I decided that I should use 10ml of H2 02. I also decided to carry on my experiments, instead of using five minutes I chose 2.5 minutes.
Obtaining evidence
I obtained my results by carefully following my plan and method. The results I obtained were as follows:
21C
30C
40C
50C
60C
Analysis
I have drawn five graphs, all of them showing the total of oxygen evolved at each test and showing the average amount of oxygen evolved over two and a half minutes.
My second graph shows that as the starch is increased the reaction is faster and more oxygen is evolved, until there is no starch left when the amount decreases. This is shown by the graph finishing in more of a straight line and this is because the enzyme became denatured and no more oxygen was produced because an enzyme substrate complex could not be formed. There is one anomalous result for 6ml starch and 4ml water. This could be due to the fact that the stopwatch was misread or the bung might have been forced off the test tube during the experiment so that no gas was collected.
My first graph shows that the optimum amount for catalase is10ml. This is because at 2ml the enzyme became denatured and could not form an enzyme substrate complex, therefore it produced no oxygen. At 4ml and 2ml there was less oxygen evolved because the water has diluted to and slowed the reaction by allot the Hydrogen Peroxide molecules had less kinetic energy and so there were fewer collisions and fewer enzyme-substrate complexes were formed, so less oxygen was evolved.
Evaluation
My results are really reliable and accurate as they prove my prediction, which was that, the catalase would break down the hydrogen peroxide down best when there was no water. My results are good enough to support a firm conclusion and my conclusion is safe.
I have already identified anomalous results in the previous section.
In my investigation I think the following areas should be improved next time:
¨ More repeats
¨ Checking bung regularly
¨ Using a more reliable stopwatch. Overall, I think my investigation was successful.