If these variables were not controlled I would not get accurate results because there would be no consistence and results may differ due to change in variables.
Safety Precautions
While carrying out this investigation I will follow these safety rules:
- Keep all apparatus away from the edge of the desk to prevent breakages.
- Not to rush about and misbehave as accidents may occur.
- I will have to be careful when using the Hydrogen Peroxide, as it is a corrosive chemical, so I will attempt to overcome this problem by wearing goggles.
- I will be careful whilst using a knife as it can cut through the skin.
Preliminary work
I experimented what sized potato cuttings would be a good size i.e. large surface area to carry out my actual experiment. I experimented potato’s, to find a shape and size small enough to fit into a chronicle flask and at the same time good enough to give results.
Results of preliminary work:
Overall, I did 8 experiments on different sizes. As you can see my results varied.
In my actual experiment from my preliminary results I found out that it’s best to use whole numbers as it is simpler to accurately cut the potato in centimetres.
I have chosen the dimension 1 by 1 by 6 to do in my actual experiment, as it produced the most oxygen by far.
Apparatus
I have decided to use the following equipment in order to carry out my experiment:
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20 cm3 Measuring Cylinder
Digital Stop clock
- Knife
- Water
- Bung
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Plastic ruler.
- Safety Goggles
- Container
- Cronical flask
- Test tube
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30 cm3 of Hydrogen Peroxide
- Potato
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Delivery Tube
Method
I will set up apparatus as required. I will cut my potato into cubed shapes with the dimensions 1 by 1 by 6. I will then cut them into shapes with different surface are but the same volume. To be accurate I will cut the potato using a knife and a ruler. The dimensions of the potato I will be experimenting are (1 by 1 by 6), (1,1,3), (1,1,2), (1,1,1.5) and (1,1,1). Each of these shapes will be made by cutting the original potato size (1,1,6) into different sections. For example for the second dimension (1,1,3) I will cut the original potato size in half. Then I will put both the potatoes of dimension (1,1,3) into the chronicle flask.
I will then measure 30cm3 of the hydrogen peroxide solution. Then I will pour the solution inside the chronicle flask and put the hydrogen peroxide in the test tube. Fill up the container with water and then fill the measuring cylinder up to the top with 20cm2 of water. Then I will join the delivery tube to the chronicle flask. Next I will put my hand over the top of the measuring cylinder and put it upside down in the container making sure that no air gets into the measuring cylinder.
Then I will add the potato shapes to the 30cm3 of hydrogen peroxide. Then the reaction will start and I will put on the bung. This is so the oxygen released from the reaction will travel up the delivery tube into the measuring cylinder so I can measure how much oxygen is being released. I am collecting oxygen over water because it is lighter and less soluble then water.
Subsequently after timing a minute I will record the volume of oxygen produced. I will do this three times for each measurement so I get an average, as this will make the results more accurate.
Prediction
I predict, the greater the surface area of the potato the greater the rate of oxygen produced. Also the rate of the oxygen being given off should be directly proportional to each other.
This is because when the chips have more surface areas then there will have greater contact for the hydrogen peroxide to diffuse into the potato tissue, so more catalase enzymes are working as the same time, therefore the faster the rate of reaction. The energy needed to start a reaction is called its activation energy and a catalyst lowers the activation energy. This means that the decomposition of Hydrogen peroxide will now have enough energy to over come the activation energy barrier.
Enzymes are large molecules and proteins. Each different enzyme has its own special shape. The reactants fit into the enzyme, like a lock and key. The reactant should slot into enzymes at its active site.
Results
My graph shows a linear relationship as it has strong positive correlation. When the surface area was only 26 cm2 the amount of oxygen produced was 12.1 cm3 . However when I increased the surface area by 2cm2 to 28cm2 the amount of oxygen produced was also increased by 2cm3 to 14.1cm3. This shows that the surface area and the rate of oxygen production are directly proportional. This proves that my prediction was correct.
When I drew the line of best fit, I found out that as the surface areas of the potato increases, the volume of oxygen collected in 1 minutes also increases. This is because when the potato has more surface areas then there will have more areas for the hydrogen peroxide to diffuse into the potato tissue, so more catalse enzymes are working as the same time, therefore the faster the rate of reaction.
Conclusion
From looking at the table and my graph I have observed that it has proven my predictions to be right. As the surface area increases so does the amount of oxygen produced. Also the increase is directly proportional.
The plotted results on the graph produce a straight line of best fit to begin with which then goes into a curve of steadily decreasing gradient. The only anomalies are the results at dimensions 1,1,1.5 and 1,1,1. The result at 1,1,1.5 and 1,1,1 are very slightly above the line of best fit. This is probably due to an experimental error.
There were some difficulties while I carried out this investigation which may have caused small anomles. It was very difficult to cut the potatoes into pieces, especially when it reached cutting the dimension 1 by 1 by 1.
It was also hard to read the readings at exactly 1 minute because people have reaction time so this can delay the readings. Also when I was putting the potato chips into the chronicle flask, maybe two potato chips were sticking together, this would decreased the surface area which decreases the amount of oxygen produced.
I need to keep the temperature constant throughout the whole experiment but it was difficult because this is an exothermic reaction, which means when its reacted, it gave out heat, so the temperature may have changed during the experiment.
In order to improve my experiment, 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. Maybe I could increase the time to let the reaction react, so more oxygen will be produced, increasing the accuracy of the results.
I could use a vernier calliper to measure the length of the chips instead of a ruler because this can provide measurements to 2 decimal places, therefore this would increase the accuracy of the results.