Investigate the effect of increasing the surface area of potato on the breakdown of hydrogen peroxide

Other factors also affecting enzyme activity:

1. Temperature – a higher temperature speeds up the movement of substrate molecules. The enzymes themselves gain energy and they begin to vibrate. Too much vibration, however, can cause the denaturation of enzymes; the substrate can no longer bind with the active site, therefore it can no longer work.
2. pH – changing the acid or base conditions around an enzyme molecule affects its three-dimensional shape and can denature the enzyme. Each enzyme has its own optimum pH (the pH it works best at).

Prediction

In this experiment, I predict that as we increase the surface area of the potato cubes, the amount of oxygen produced will also increase. As the surface area doubles, the amount of gas produced should also double because double the amount of catalase enzymes can work to break down the hydrogen peroxide. Each catalase active site can breakdown 107 hydrogen peroxide molecules per second. If more active sites are exposed, more compounds can join and be split by the catalase enzyme. The reaction will increase with increasing enzyme concentration when molecules of hydrogen peroxide are freely available. There will be an optimal point at which all the enzyme active sites are filled and operating at each amount of catalase. At this point the reaction will stop producing more gas when the hydrogen peroxide has been broken down into water and oxygen, water is unaffected by catalase.

The formula for this reaction is:

Catalase + Hydrogen peroxide → Water + Oxygen

2H2O2 → 2 H2O (l) + O2 (g)

The reasons for my predictions could also be explained using the collision theory. The collision theory states that 'the greater the surface area, the more chance of collisions occurring so the faster the rate of reaction.'

For this experiment, we will cut out potato cubes of the same size. We will then start by placing 3 cubes into a test tube with a bung connected to a pipe that stretches out from inside the test-tube into a measuring cylinder filled with water, which is placed inside another container of water. Add the hydrogen peroxide to the test tube with the potatoes and close it with the bung. The product released from the reaction will travel along into the pipe and go straight into the measuring cylinder. When the oxygen enters the cylinder, it displaces the water in it and collects at the top of the cylinder. This happens because the oxygen is lighter than the water and can push it aside to reach the top. Once the oxygen is collected within a period of five minutes, we can measure how much has collected in it using the markings on the cylinder. You then repeat the experiment, increasing the number of cubes by 1 each time.

Apparatus

1. test tube
2. measuring cylinder
3. plastics container with water
4. bung connected to pipe
5. hydrogen peroxide (20cm3)
6. potatoes (1cm3)

Safety

1. I will have to be careful using the hydrogen peroxide, as it's a corrosive chemical. Therefore safety goggles should be worn at all times throughout the experiment.
2. Clothes should be tucked in
3. Long hair should be tied back
4. Stand up at all times during the experiment
5. Bags should be tucked under the side benches to prevent accidents that can cause damage to the lab.
6. All spillages must be reported to the teacher immediately.

Method

1. Cut equal sized pieces (1cm3) of potatoes with a blade knife, making sure that they have an equal surface area.
2. Fill a plastic container with water
3. Fill a test tube with 20 cm3 hydrogen peroxide and then slip the potatoes in.
4. Immediately place a bung in the top of the test tube which is connected with a pipe whose end is placed under the measuring cylinder.
5. Start the stop watch and leave in running for 5 minutes only.
6. At the end of the five minutes, stop the stop watch and read off the measuring cylinder the amount of oxygen given off and record it.
7. Repeat steps 3 – 6 again and each time increase the number of potato chips by one until you reach to 10 chips, then the experiment is over.

Diagram

Variables

Controlled variables:

1. variety of potatoes
2. size of potato cubes
3. concentration of hydrogen peroxide
4. volume of hydrogen peroxide
5. pH levels
6. time

Independent variable:

• Number of potatoes – this is a continuous variable because it can have any variable over a continuous range.

Dependant variable:

• Volume of oxygen produced – this is the volume released in a certain amount of time (in this case 5 minutes). It's also a continuous variable.

Preliminary results

Results

Graph of the surface area of the potato cubes against the volume of gas collected

Conclusion

In conclusion after we had successfully completed our experiment and drawn up our graphs we came to notice that our prediction was correct.  My prediction was that as you increase the number of potato chips, the volume of gas given off would also increase.  This can bee shown by my straight –line graph which shows a positive correlation.  We also could see from our results that as we double the surface area of the potato chips the volume of gas produced would also double.

Theoretical conclusion

My results can be explained using the collision theory which states that:

‘The greater the surface area, the higher chance of collisions, hence the faster the rate of reaction’.

That’s why I’ve noticed a steady increase in the amount of oxygen produced as a result of the reaction.

Analysis

Whilst doing the experiment the amount of oxygen produced was recorded and used to draw a graph this would show if the hypothesis predicted at the start of the investigation has been proved correct or rejected. From the graph I could see that the volume of oxygen produced and the surface area of potato chips are directly proportional to each other.

The gradient of the graph will give a value of 'change is Y'- (volume of oxygen) / 'change in X'- (surface area of cube)

Gradient: 

Change in Y = 15.35 – 3.75 = 11.6

Change in X = 60 – 18 = 42

= 11.6 / 42

= 0.28

The results from the graph give a clear indication that there is a very strong positive correlation between the surface area of potatoes and the volume of oxygen gas given off.

Evaluation

In general, the experimental procedure went well and the results are evidence of this. The results follow a regular or expectable pattern. There were no anomalous results since all the points where on the line or quite close.

To have made my experiment more accurate and reliable I would’ve made the following improvements:

• Use a smaller measuring cylinder than a big one as its much precise to read your results from
• The temperature should have been kept constant at all times during the experiment so that the results would be more fair
• Finally, weighing the potato chips would have insured that my potato chips have the same surface area therefore making my results even more accurate.