In this investigation the aim is to find out whether the concentration of hydrogen peroxide affects the rate at which catalase breaks it down.

Method:  The equipment was brought together which consisted of the following:  Potato, measuring cylinder, hydrogen peroxide, scalpel, cam stand, cork borer, bowl, pipe. These items were then assembled. (Look at diagram below)

The steps taken to carry out this experiment are as follows:

1. Equipment was brought together

2. Potato was peeled and a cork borer obtained cylinder shaped potato. Then this was divided into 6 equal 1cm pieces with a sharp scalpel.

3. The 6 pieces of potato were then added to the test-tube.

4. To this test tube, 20ml of hydrogen peroxide was added, and a small pipe was attached to the measuring cylinder, which was placed under water. (See diagram above)

5. Time taken for water (in measuring cylinder) to decrease by 5ml, producing oxygen.

6. The test-tube was then cleaned out by water, and 6x1 potato pieces were thrown away.

7. Steps 1,2,3,4,5 were repeated two times to give average time taken values.

8. Steps 1,2,3,4,5, and 6 were repeated again but with the following volumes of hydrogen peroxide and water.

To make sure that my experiment is fair I will make sure that I completely rinse all of my apparatus. I will do this to remove any particles from previous experiments so that there are the right amount of particles and therefore the right concentration. I will also make sure that I use the same volumes of each liquid to keep the concentration the same and keep the number of particles the same. I will not stir the chemicals at all and I will try to move them around as little as possible. This is to prevent any unwanted collisions, which may inadvertently speed up the rate of reaction.

Results:  (graph on graph paper)

Conclusion: The prediction is correct, because the graph has a negative gradient, this means as hydrogen peroxide volume increases (therefore concentration) the time taken for 5ml of oxygen to evolve decreases, this clearly shown on my constructed graph. Note: time taken for 10ml of oxygen to evolve is indirectly proportional to rate of catalase. As time decreases, rate increases. This means catalase at a faster rate at higher concentrations of hydrogen peroxide and vice versa. If a graph of rate vs. concentration was constructed using this data, the graph would have a positive gradient. (Look at fig 2.) It was observed that as you increase the quantity of water the prepared hydrogen peroxide solutions, the time taken to produce 10ml of oxygen (in the measuring cylinder) increases. This has backed up my prediction, in which I stated that the time to make oxygen would increase. The theory I used was the kinetic theory in which it states, if there are less atoms, there will be less collisions because it takes more time for catalase to catalyse this reaction: (look at fig 1.)

My results back up this theory because, in my results as we increased the water in the concentration on hydrogen peroxide, the time increased.

 

Evaluation:  The data collected was substantial enough for the accuracy of the experiment; it was fairly reliable meaning the results collected were mostly expected. When I added the line of best fit on my results graph, I could then see if there were any anomalous, and then some basic conclusions could be produced but also the results were accurate enough to back up my prediction and the theory I used which was the kinetic theory, they were both backed quite substantially.

Looking back on the experiment there were many ways to improve I can use an implement called thermostatically controlled water—bath. This can keep the hydrogen peroxide in a constant temperature to make the experiment more fair and accurate. I can increase the size of the potato chip in order to help me to cut the chips into pieces more accurate and easier. To stop the potato chips to dry out when I get to the experiment I could use cling film to cover them or not cutting them till the end. I could cut the potato pieces by using a electric ruler, it would virtually make every potato the same size, and it can go down to 4 decimal places. I could see the mass of each potato by weighing them so then each potato could be equal. Measuring the oxygen is a little harder; to measure oxygen there may be equipment that is not available to me, so this cannot be carried out.

There were no anomalous results in this experiment. The results are reliable and sufficient enough to support the prediction. The method could be improved by stating certain reasons for doing certain actions e.g. peeling the potatoes, cleaning out the test tubes, etc. Doing some pre-liminary work, which would have been very helpful because then we could make better observations and predictions about this experiment, could have extended the investigation. We also could have done each concentration exercise each lesson, so we could spend more time on our method. I am quite pleased with the outcome of my exercise and the results.