To do the experiment I need to keep every variable constant apart from one. The variable I am going to change is the concentration of the Hydrogen Peroxide. Therefore I have to keep the amount of catalase, the temperature, the amount of Hydrogen Peroxide and the time it is measured at the same. To decide the amounts for each variable I need to conduct preliminary experiments. This will make sure that the experiment is easily measurable (doesn’t react too fast or slow to measure.)
Preliminary Experimentation
The concentrations I want to use for my experiment are:
So I decided to use 10 ml of catalase (celery juice) and tested the concentration at 1ml of Hydrogen Peroxide and 9ml of water. The temperature was 21º and the volume of gas was measured at 60 seconds.
This experiment was extremely slow and produced nearly no result so I decided to try 5ml of Hydrogen Peroxide and 5ml of water still measuring the gas at 60 seconds, the temperature at 21º and using 10 ml of catalase.
This experiment was still quite slow so this time the time was changed to 120seconds keeping the amount of Hydrogen Peroxide at 5ml, the water at 5ml, the catalase at 10ml and the temperature at 21º.
This Proved to be fine and it was easy to measure the results. Now I need to try the concentration at 10 ml Hydrogen Peroxide and no water still keeping the other variables the same.
This also worked well so I decided the final values to test will be:
Apparatus
- Bowl of water
- Conical Flask
- Bung and delivery tube
- Measuring Cylinder
- Stop Watch/Clock
- Clamp and Clamp Stand
- Hydrogen Peroxide
- Water
- Catalase
Method
- Set up apparatus as shown
- Measure out and mix the Hydrogen Peroxide and water in the amounts needed in table above e.g. 5ml Hydrogen Peroxide and 5ml of water and put it in the conical flask.
- Add the catalase to the conical flask, immediately replace the bung and start the stop watch/clock.
- After 120 seconds record the amount of gas that has been produced in the measuring cylinder.
- Repeat each concentration three times and make an average.
- Repeat experiment for the other concentrations.
Prediction
I predict that if I increase the H2O2 concentration this will increase the rate of catalyse activity because there will be more H2O2 particles to bump into the active sites, resulting in more chemical reactions caused by successful collisions between the active site of the enzyme (catalase) and the substrate (hydrogen peroxide).
Obtaining Evidence
Analysis
Form the graph, which is a straight line, I can see that the concentration of the H2O2 is directly proportional to the amount of O2 produced. To work out the proportion I worked out the gradient of the graph.
GRADIENT= Y
X
=8
1
=8
=8ml of O2 per 1ml of H2O2 .
The reaction took place faster as the concentration of the H2O2 is increased because as the concentration increases there are more particles of H2O2 bumping into the enzymes (catalase) active sites causing more successful collisions between the enzyme (catalase) and the substrate (H2O2 ). This results in an increase of O2 production.
This supports my prediction that if the H2O2 concentration is increased the rate of catalyse activity will also increase.
Evaluation
It is clear from the graph that there are 2 anomalous results in the experiment. There are many reasons why these anomalies occur.
The first reason why the experiment wasn’t entirely accurate was when the catalase was added to the H2O2 there will always be a space of time between the catalase entering the H2O2 and the bung being replaced. Therefore some of the O2 will have already escaped.
Another problem with the experiment was keeping the temperature constant throughout the experiment. If the temperature fluctuated slightly the reaction could have speed up/slowed down therefore producing anomalous results.
Another problem was how the gas was measured. Because it was measured in an upside down measuring cylinder results can easily be misread. Also the large scale on the measuring cylinder also made it difficult to read results accurately. This meant tat many of the results were rounded up or down to nearest readable measurement so the results weren’t precise.
I could have improved the experiment to get more accurate results if I change the following things.
I could have used a smaller measuring cylinder with a smaller scale so the results were more accurate and not rounded up to the nearest readable measurement.
I could have also changed the concentration in smaller amounts at a time for e.g. increasing the concentration by 0.5ml at a time rather than 1ml.
Finally I could have conducted 4 or 5 times in order to calculate a more accurate average.
