The surface area will show how the increasing surface will raise the rate of reaction. I will divide a piece of potato, from one length, into various lengths of equal size but in sections/parts (i.e. 3cm length potato cut into 2 parts of length 1.5cm). I will be measuring the amount of oxygen released from each section of these, breaking down the hydrogen peroxide.
Apparatus List
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2 Measuring cylinders – 10cm3 for measuring the hydrogen peroxide and gathering the oxygen produced
- Delivery tube – Carry the oxygen produced to the measuring cylinder.
- Potatoes – The source for the enzyme, Catalase.
- Scalpel – Dividing the potato up cleanly and precisely.
- Ruler – Measuring the length of the potato pieces accurately
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100% H2O2 – Substrate for experiment. Constant Molar solution.
- Boiling Tubes – Holding substances
- Bung – To keep the oxygen from escaping the boiling tube.
- Stop watch – Calculate the time of reaction.
- Water – prevents gas released into measuring cylinder from escaping.
- Goggles – Eye protection.
Fair Test?
To ensure that results are not biased in any way, these factors must be kept constant at all times:
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Keeping the volume and concentration of H2O2 constant – it is not the variable that we are investigating. If it is changed, it will alter results.
- Using the same type of potato – To stop any differentiation between using a different potato as the concentration of catalase in another variety of potato may be different, changing the results.
- Equipment – Prevent any biased tools or changed sizes (I.e. Borer size) as it could change the results dramatically.
- Cleanliness – Wash out the tubes after usage to prevent any reaction occurring beforehand
However there are some factors that would be better to have kept constant but are unable to:
- Room Temperature – As we are working with enzymes, the temperature at which the enzymes work. This could be controlled by air conditioning, monitoring the change in temperature, s they do in hospital theatres.
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Safety points.
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H2O2 – A poisonous/irritable substance, so DO NOT drink it in anyway.
- Wear goggles at all times to prevent spillage into the eyes because it will poison and damage your eyes.
- If there is a spillage, beware of cuts or wounds as the toxin will enter your bloodstream and poison you. Wash off immediately.
Diagram
Brief Method and Results Table
There were originally 2 methods to choose from that would present my results effectively:
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Bubble Collection – Counting the number of O2 bubbles being produced.
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Water Displacement – by O2 in the measuring cylinder.
I chose the second method because the first is less accurate as there may be variation in the size of bubbles and therefore the accuracy of estimating the volume of O2 is very difficult. There is also the fact that counting bubbles that may be rapidly produced is hard to count. Whereas the second method provides me with a fixed volume and overall, a more accurate result.
To show that this method can prove to be effective, I have done some preliminary work to see whether it is efficient:
These results have determined that these measurements are sufficient enough to plot a graph. This experiment had also been completed within the time limit given. Therefore it should be able to be repeated easily. It also has shown the most effective time for the reaction to take place and the amount of H2O2 that should be used. The lengths are easy to measure without any complications. This method is very efficient in getting a good range of results.
This is a brief method of what will occur:
- Bore 5 potato chips.
- Measure with ruler and cut equal length.
- Split them accordingly.
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Place chips into H2O2.
- Use stopwatch to time reaction.
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After a certain time, record the O2 gained in cylinder.
- Repeat twice to obtain 3 sets of results and increase accuracy.
This represents the general shape of the graph made from preliminary work:
From this I can predict that:
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As the number of parts increases/the length decreases, the amount of O2 released increases – because there is a larger surface area, providing more active sites for reactions to occur.
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Therefore the number of parts is proportional to the amount of O2 release.
- This prediction could be quantitative. Therefore if I double the parts I should obtain double the volume in the 240 seconds given.
Obtaining Evidence.
Detailed Method.
- Using a Borer size 5 bore out 5 potato chips.
- Setup the apparatus as shown in the diagram.
- Measure them uniformly (3cm) and use a knife to cut them down to size.
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Splitting them accordingly – The 1st piece will remain 3 cm, while the 2nd will be split into 2 parts and halved in length. The 3rd, split into 3 parts etc.
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Place 10cm3 of H2O2 into the boiling tube and place one set of potato chips into the corresponding tubes.
- Start and end the stopwatch after 240 seconds have passed (4 minutes).
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During the reaction, the O2 will be transferred to the measuring cylinder.
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Disconnect the delivery tube from the cylinder and record the amount of O2 present.
- Repeat the process twice to obtain 3 sets of results for better accuracy.
Results.
Set1
Set 2
Set 3
The 3 sets of results were taken within 3 weeks, one set each week, on the same day. They show that I have taken the results efficiently and as accurate as possible. The average O2 released was calculated by adding up the amount of O2 from the 3 sets and dividing them by 3. This will give an overall average and a more accurate result.
I have plotted the graph on graph paper.
Conclusion
Most of my results indicate that the higher the number of parts, the higher the amount of oxygen is released. As you can see from the averages, the values steadily increase from 5.3 to 7.0 cm3. The graph also shows that my prediction was correct in stating that the amount of oxygen is proportional to the amount of surface area exposed to the H2O2.
The graph slopes downwards gradually decreasing as the length increases without any rapid increases or decreases. This shows that the larger the surface area, the greater the rate of reaction. This is explained by the availability of active sites for the substrate to fit into. With a reduced surface area, the enzymes are clumped up into groups, cutting off some of the active sites for the substrate to enter and react. However a larger surface area has more enzymes that are spread out, allowing them to collide with a substrate molecule and has a better chance to react successfully. Therefore there is more of a chance that the catalase molecule will collide with a hydrogen peroxide molecule producing oxygen products.
The larger surface area will, in turn, produce more O2, thus a bigger volume, producing a faster rate of reaction. This means that my prediction is correct and backed up by the collision theory and scientific knowledge.
Evaluation
This experiment has been very successful as quite a few results have been taken and an overall conclusion has been derived from it. However there have been some anomalous results in each set, overall, the anomalous result being the 3rd tube, as it drifts from 5.4 cm3 to 5.1 cm3. This may have been misjudgement on my account as I was not accurate enough or the technique was not proper. However other results have proven to be successful as the values do increase as the surface areas enlarge (5.3 – 7.1cm3).
To increase the accuracy, if there were the tools, I would use a gas syringe to measure more accurately the amount of O2 gathered, from the experiment. Other pieces of hi-tech equipment such as the automatic-pipette, which measures extremely accurately solutions and a “buffer” which controls the pH of the reaction to make sure it does not drift from the optimum. The potatoes could have been saggy and have a low concentration of catalase enzymes. Whereas the other potato that I used had a much higher concentration of enzymes within it, manipulating the results by a large margin.
The problems with the technique would be numerous but uncontrollable in some cases, such as timing. Everyone does not have the same reaction time; therefore the degree at which you stop the watch at exactly the right time is negotiable. It is also evident that it is hard when you are going to start the stopwatch, whether it is when you close the bung or some other time. It becomes hard to start the timer at exactly the same time; every time. By hitting the delivery tube by mistake could release an oxygen bubble, raising the values by maybe 1cm3, which could make a difference.
You may accidentally heat up equipment, such as test tubes when you experiment on them, thus maybe speeding up the rate at which the enzyme works. This could be avoided by minimal touching of equipment. The temperature of room was varied from 18o – 25o C, having an effect on the overall result. The froth/bubbles coming up off the surface from accidental shaking would speed up the reaction, as you are giving the molecules kinetic energy to react successfully together. This can be stopped by being careful not to shake or if you are shaking, shake on every test that is carried out. There is air that is already trapped in the tube, so that might add an extra few cm3 to the recording, altering the result.
For method modification, I may choose to elongate the time given to 5 minutes as 4 minutes may not be long enough, with the sufficient amount of time. Using different types of bore size would back up this theory or comparing these results with another set of 3 but using a different sort of potato. Having an increased range of results will increase the accuracy by a lot.
Investigating different variables will vary the theories made from other results, such as the temperature or the concentration of enzymes/substrates.
Overall, the experiment went smoothly but I feel that the downfall was in the accuracy of the time, and the lack of equipment involved measuring even more accurately.
Although there are flaws, next time, I will be more accurate, taking into account these factors but my conclusion believe, is reliable and true, even though I had one anomalous result.
Bibliography
GCSE BIOLOGY – D.G. Mackean