Below is a diagram to show the theory-
Therefore as part of my investigation I will choose to investigate what the effects of increasing the number of slices of a potato chip as you add it to hydrogen peroxide.
Prediction: -
For my hypothesis I would say that there would be a steady increase of the amount of oxygen collected as you increase the number of slices of potato to add to the hydrogen peroxide. This is purely based on the hypothesis I made earlier on the enzyme molecule and the substrate.
Consequently the results should show a fairly strong positive correlation.
Here is a graph to illustrate what I think the results should show presented in a graph: -
Amount of oxygen collected
In cm3
Number of slices
In the graph it shows that the number of slices is directly proportional to the number of slices. This may not be the case when the experiment is done.
Explaining Variables: -
Some of the variables that will be relevant to this investigation are also to be kept constant: -
Constant Variables Input and Output Variables
-
Type of Potato Number of slices of potato
-
Size of potato Volume of oxygen produced
Amount of Hydrogen Peroxide
Temperature *
Shape of Potato
- Time Counted
- Same Potato used throughout
Experiment.
Same apparatus used throughout
Experiment
- Concentration of Hydrogen Peroxide
*-During the Experiment the water might heat up and therefore affect the results. In order to avoid this problem, I will use a thermometer to keep an eye on the temperature. Although performing the experiment at a temperature slightly higher than room temperature it is important that the room temperature doesn’t go above 25oC.
Of these the variables will be input and output, and the input variable (independent) will be the Number of slices of potato, and the output variable (dependent) will be the Volume of oxygen produced. The other variables will have to be kept constant, to make sure that only the Number of slices of potato, Volume of oxygen produced by the Elodea are investigated. I will use the same potato so the Size, shape and type of potato will be kept constant.
The variables above strictly need to be controlled; otherwise I would expect that there would be many anomalous results. To avoid these anomalous results the variables have to be very accurate. E.g.- the slices of the potato chip have to be exactly the same in length and also the amount of hydrogen peroxide strictly has to be constant throughout the experiment or it will affect the rate of enzyme reaction.
It will ensure a fair test if each variable is considered to be important because many have to be kept constant apart from the input and out put variable, so that they are the only variables found out in the experiment.
If this is done it will ensure a fair test.
The apparatus (Safety Precautions): -
The apparatus-
Water Supply
Beaker (x2) (capacity of 100cm3)
Potato (Same throughout the experiment)
Measuring Cylinder* (capacity of 20cm3)
Delivery Tube
Test Tube with bung
Thermometer (accurate to ±1 oC)
Supply of 20 vols. Hydrogen Peroxide (50cm3)
Scalpel
White Tile
Stopwatch (accurate to 100th of a second)
To make things fair I will use the same glassware in the apparatus, to do the experiment.
*: - The measuring cylinder must definitely be filled with water so that we can count the capacity of oxygen collected during the experiment, we should be able to count the bubbles (oxygen) as we would be able to see them.
The apparatus will be set up as shown in the diagram shown below: -
Safety Precautions:
I will have to be careful when using the Hydrogen Peroxide, as it is an irritant, so I will attempt to overcome this problem by wearing goggles. Hydrogen Peroxide is a bleaching agent, so I will be wearing a lab coat so it doesn’t bleach my clothes. I will be using sharp razors during the experiment so I will have to be cautious about that. A mercury thermometer will also be used so it is important that the mercury is not inhaled in case of a breakage. I will keep some sulphur alongside the apparatus just in case it if were to occur.
Method: -
The apparatus will be set up as shown on the previous page.
The potato chip will be cut into thin slices (2mm in length), according to however many are needed in the experiment.
Once cut, the potatoes will then be added to a test tube containing 5cm3 of substrate (Hydrogen Peroxide). From the moment both the substrate and the potato are put in, a bung will be placed onto the test tube, which is attached to a delivery tube.
The oxygen given off due to the reaction will then be collected in a measuring cylinder whose top end is in the large beaker containing water with the delivery tube going in it.
The reaction will be timed for 1 minute and then the amount of oxygen collected in cm3 in the measuring cylinder will be recorded. The experiment will be done according to the input variable (number of slices) and therefore will be done by increasing the number of slices of potato each time.
The thermometer will be used each time and placed in the beaker full of water to make sure the temperature is constant.
Modifications to plan: -
Once I began changing the number of slices of potato (input variable) and measuring the amount of oxygen collected (outcome) I realised that I will cut the slices of potato so that they have dimensions of 1cm x 1cm x0.2cm this way all the slices would be able to fit in the test tube, if I were to use 10. I have also decreased the number of slices from 12 to 10 because I had found out that the froth raised too far up the rest tube.
I had also observed from my preliminary work that I will immediately record the amount of oxygen collected when the time limit was up. The one thing I had changed was instead of timing the experiment per 2 minutes, I will half it and measure the oxygen collected in cm3 /min.
Also I had also found out that when you place one end of the delivery tube under the water and the other in the test tube, water collects at the bottom of the delivery tube if you just put it in the water without placing the measuring cylinder on the other side. This not only slows the transfer of oxygen from the test tube to the measuring cylinder, but also causes anomalous results.
Here is a diagram outlining the problem: -
Another problem which should be considered seriously would be that when you place the potato slices (1cmx1cmx0.2cm) in the test tube you have too make sure that they aren’t stacked on top of each other in the original form of the chip. This causes the problem of a reduced surface area and therefore it will take far longer to get the amount of oxygen collected.
Instead when using 2 or more potato slices in the experiment, you should scatter them and try and expose as much of the surface area as you can, so that the hydrogen peroxide can get to it. This will hopefully increase the rate of reaction and the results would be more positive and reliable.
Here is a diagram outlining the problem: -
Preliminary Results:
The preliminary results support my hypothesis that as you increase the number of slices, the amount of oxygen collected will also increase. Although these were preliminary results I found out that they weren’t that many mistakes, this indicated to me that by controlling some of the variables I was able to exclude the factor of getting anomalous results.
By doing the preliminary results I found out that I would not go above 10 as the number of slices, this is because the froth rises too much once the reaction takes place. Also a you can see in the preliminary results, I had used 2 potato slices then and then increased in 1 to 3 slices, this did not prove to be effective because there was hardly a noticeable change in the amount of oxygen collected. So when I conduct the results for my experiments again, I will go in intervals of two.
I felt that by doing the preliminary results I was able to identify any mistakes I was making in the experiment and also get a fair idea of how to record the results, as well as finding out the range, e.g.- number of slices. So I will take the observations that I found out whilst doing preliminary work into consideration, as it will be useful once I record the actual data.
Strength of Evidence: -
To get a more accurate spread of data, the results must me repeated three times, to get an average at the end, which will be used, in the graph. Also by making sure all the measurements are recorded accurately, they should all be double-checked.
