The Effect Of Changing The Surface Area Of Potato On The Breakdown Of Hydrogen Peroxide.

Preliminary Work

We will carry out preliminary experiments and obtain preliminary results so that when we come to doing the original experiments we can solve the problems located in the preliminary work, and solve them for the original work. There are also other aspects we must find out from our preliminary work, which are:

• What minimum, maximum and medium surface areas we will use, that produce a sufficient volume, but not too much either.
• What amount of time we will allow for the reactions to take place, so that we will have enough time to do the experiments within class and to also do repeats, from which we can calculate averages.
• What volume of hydrogen peroxide shall be used
• How to measure the amount of oxygen produced

In the following preliminary results we are looking for a surface area, which produces a sufficient amount of oxygen gas, but not too much either.

To carry out these preliminaries we decided to use 25cm3 of hydrogen peroxide, since we found that it could cover all of the cubes we were going to test, and it filled most of the boiling tube, and would not allow a larger volume then this.

We also needed to establish a time frame for the reaction to take place in our preliminary results. We shall start with 1 minute, and continue on to 2, 3, 4 etc. until we find a timeframe, along with the surface area which produces a sufficient and measurable amount of oxygen. We shall start the preliminaries with small timeframes because it will allow us to carry out all the preliminaries within the lessons.

The following table of preliminary results shall help me to decide the time frame and the minimum surface area to use:

From this table you can see, under a timeframe of 1 minute, and with 1 cube of surface area 6cm2 we did not produce a measurable amount of oxygen: 0cm3, and it was the same when we raised the time frame to 2 minutes with 12cm2. We then raised the timeframe to 3 minutes, and the surface area to 18cm2, and produced a measurable amount of oxygen; 5cm3, but this volume is still not sufficient enough, so we tested with a surface area of 24cm2. In 3 minutes this surface area produced 7cm3 of oxygen, which is a sufficient and measurable amount. Hence I have decided for the minimum surface area for our actual tests to be 24cm2 since it produced a measurable and sufficient amount of oxygen in 3 minutes. The timeframe in the actual tests shall be 3 minutes for each reaction, since we found that it allowed us to carry out many tests in a small amount of time, and since we only have around 5 hours of class time to carry out the tests, it is important we are able to finish all the tests in time.

Now, I need to do some preliminary work to establish what maximum surface area I shall use, and I also need to establish 3 other surface areas excluding the minimum and maximum surface areas, but ranging in between them(medium surface areas). Hence in this preliminary I will have to look for 4 surface areas, in a timeframe of 3 minutes per test:

From these tests I found that 120cm2 produced 41cm3 of oxygen, since we are using a 50cm3 measuring cylinder, using a higher surface area then this could cause problems if it exceeded 50cm3, hence I shall use this as the maximum surface area.

I noticed, that at 72cm2 and above the cubes started to clump together, which means that many sides of the cubes were blocked, and hence many sides full of catalase were not reacting with the hydrogen peroxide. Also, from 72cm2 and above since the boiling tube in which the reaction was being carried out was small, the froth of the reaction started to be sucked through the gas tube, and end up with the oxygen in the measuring cylinder. This affected the results, and hence that’s why we have such a big gap in volume of oxygen produced for the surface areas 96cm2 120 cm2, since the froth took up a large space.

I shall use the surface areas 48 cm2, 72 cm2, and 96cm2 as the 3 medium surface areas to test. This is because they don’t produce too much froth, and the clumping is also not so much, it gets worse as the number of cubes is increased.

Now I must decide how to measure the oxygen gas being produced. I can either count bubbles emitting from the delivery tube, or I could use a measuring cylinder to measure the volume produced in cm3. The problem with counting the bubbles is, that it can not be made accurately sure whether the volume in each bubble is the same, and secondly, some bubbles may be missed or miscounted if the rate of bubbles emerging is really fast, both of these disadvantages make the bubble technique extremely inaccurate. Therefore I choose to use the measuring cylinder to measure the volume of oxygen gas in cm3 displacing the water in the measuring cylinder. Since it is accurate, and easier to just measure the amount of oxygen displacing the water in the measuring cylinder. We will be using a 50cm3 measuring cylinder; we used the same technique in the preliminary tests.

• To avoid too much clumping, I chose small surface areas for when we carry out the actual tests.
• To allow all the number of cubes to submerge in the hydrogen peroxide, I shall use 25cm3, which fills up almost the whole boiling tube.
• To provide a sufficient and measurable amount of oxygen, I chose a time frame of 3 minutes and the minimum surface area to be 24cm2. since less than 3 minutes, and with smaller surface areas, we were not getting measurable amounts of oxygen gas.

Measurements

We will be measuring the volume of oxygen released when we react the catalase enzymes (on the surface of the potatoes) with the hydrogen peroxide. This reaction also produces water, but we shall ignore this.

The range of surface areas to be reacted with a constant volume of hydrogen peroxide is, 24cm2, 48cm2, 72cm2, 96cm2, and 120cm2. We shall do 3 repeats, for reliability of our results. This range was chosen because we are doubling each surface area, allowing us to prove quantative predictions.

Method

First I took a 50cm2 measuring cylinder and filled it to the brim with water, and then I took a plastic container and also filled it with water, to about half its volume. I filled both of them with water, from the same tap, so as to maintain a constant temperature. Then I placed the measuring cylinder into the plastic container, carefully, so as to not allow the water in the cylinder to be displaced by air. Then I took a boiling tube, with a bung plus delivery tube attached, and the other end of the delivery tube would be placed through the water in the container, into the measuring cylinder when the experiments would be carried out. 

Now that the apparatus was set, I had to test my first, minimum surface area: 24cm2

So I placed 4 potato cubes into the boiling tube, then before I poured in 25cm3 of hydrogen peroxide, I fitted the bung on top of the boiling tube, and placed the end of the delivery tube inside the measuring cylinder. I activated the 3-minute timer, and then we recorded the results at the end of the 3 minutes. We repeated the experiment for the surface areas: 48cm2, 72cm2, 96cm2 and 120cm2. Every time we changed the surface area, we had to refill the measuring cylinder to the brink with water again, add 25cm2 hydrogen peroxide into the boiling tube, and replace each cube with a new one.

Results

The following are the results obtained in the actual experiments, which we conducted in class.

Each test had a timeframe of 3 minutes, 6cm2 represents 1 cube, and the volume of oxygen produced is in cm3.

Drawing Conclusions³

From this graph you can clearly see that as the surface area increases, the volume of oxygen gas being produced increases. In this graph you can see, that when the surface area equaled 24cm2, the oxygen produced equaled 5 cm3, and then when we doubled the surface area, the oxygen produced also roughly doubled; 14 cm3. This supports my prediction, that as the surface area doubles so does the volume of oxygen produced. Although, out of all the results, these are the only ones that support my prediction, the others results were inaccurate, because of problems with our method of carrying out the tests.

I had predicted the volume of oxygen being produced would increase with the surface area because as the quantity of catalase enzymes increase with the surface area, this means that there are more enzymes to collide with the hydrogen peroxide in the same time slot. Also according to the collision theory, with more enzymes in the same volume of hydrogen peroxide, there is a higher probability of successful collisions between the active site of the enzymes and the substrate, and therefore with a higher rate of successful collisions then there is more hydrogen peroxide being turned into oxygen (and water) in the same amount of time.

Evaluation

Accuracy:

Since we did three repeats for each surface area, we did get reliability of the results, but I do not think that the method in which we carried out the test, would help to solve our investigation very well. We found that the 96cm2 surface area was producing anomalous results because they were not in line with the general trend.  

Practicality of Range of Results:

I think a suitable range of results were chosen, since they were chosen depending on preliminary work, and also the range goes from a very low surface area: 24cm2, to a large surface area: 120cm2. This means if there are any limits, or laws such as Hookes Law for elastic bands, then we would have been able to find them out, since we had a large surface area range being tested.

Possible Pattern or Laws & Further Work:

There is a pattern in this range of results, the volume of oxygen increases rapidly, and then the average rate near the end, decreases. This is probably because of the second last result, which is anomalous. This could probably have happened because of the clumping that started to happen. Since the boiling tube was too small, the cubes would start to clump together, as the surface area increased. Hence in the actual practical, if we would be testing 120 cm2, the surface area would be much less. This is because from clumping together, many sides of potato, filled with catalase enzymes would be blocked.  Hence, we were not getting as much oxygen produced, as we should have. Another problem caused because of the small size and tight shape of the boiling tube, the tests were being carried in, was that the foam would start to be sucked into the delivery tube and into the measuring cylinder. This would greatly affect the accuracy of our results, since the foam was not the substance we wanted to measure, and it would take up a lot more space then the oxygen, hence we got bigger results then we should have. If given time I would like to carry out the same experiment, but with an improved method, for accurate results.  We could solve both these problems, and bring the clumping to a minimum if we were to use a conical flask. The increased size at the bottom of the flask should put clumping to a minimum, although, since the bottom cubes would have one side, on the base, we would still have a decreased surface area in the practical then we’ll want. Also, with this method, the foaming problem should not take place since the conical flask is bigger, and can hold a larger volume of substance then the boiling tube. There is also another way, since we are only interested in the catalase enzymes on the potato, if we could get a simple solution of catalase enzymes, we would have no problems whatsoever with clumping. This solution can be pancreatic juice, since catalase enzymes are found in there, they are also found in the liver and saliva, to break down hydrogen peroxide.

Then with the conical flask method, if given time I would like to develop my investigation by trying much higher surface areas, to see if the volume of oxygen being produced levels off because of clumping, and also to see if there are any laws or limits I might encounter. I could do this if I were to try higher surface areas: 150 cm2, 168 cm2, 186 cm2, 205 cm2, 223 cm2 and then compare those results with the results from this investigation, and then I can see if there is any drastic change of pace in the graphs, which would tell me that there is a law or rule present.

I would also like to try to investigate how other enzymes affect the volume of oxygen produced from hydrogen peroxide, when reacted with a constant surface area of potato, containing catalase enzymes, and how it affects the amount of oxygen produced.

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