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Goggles- to protect your eyes from irritation.
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Ice cream container-to hold the water.
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Ruler- to measure the amount of potato.
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Potato borer- to cut through the potato ensuring that it is in a cylindrical shape.
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White tile- to cut the potato on.
Fair Test:
Dependant: To keep my experiment fair I must make sure that both two bits of potato are the same size (2cm long), have enough hydrogen peroxide to just cover the top of the potato completely; this would then have to be the same amount for all of the experiments. I would also need to keep the 2minutes in which the reaction takes place the same, if I change this then virtually all my results would be inaccurate.
Independent: To ensure my results back up my prediction I will change the concentration of the hydrogen peroxide (H2O2); 5, 10, 15, 20, 25, this will depend on the volume of oxygen given off in two minutes.
Safety:
The issue of safety was taken into account drawing my pilot practical and so played are large part on forming the results. Firstly, safety goggles must be worn at all times since hydrogen peroxide is a corrosive material and will do damage to the eyes. If any peroxide, despite concentration, comes onto contact with any part of the body during the experiment, measures must be taken to ensure that it is removed properly, preferably by putting the exposed area under running water. Care must be taken in the handling of the hydrogen peroxide due to it being an irritant as well as corrosive, and so if any spilt, it must be cleaned up immediately. Since some equipment is glass, special care must be taken to make sure no breakages occur and, if they do, they must be cleaned up and disposed of immediately before others injure themselves on the breakage.
Method:
- Get out the required equipment.
- Cut 2 cylindrical pieces of potato out with the potato borer.
- Put the potato on the white tile and cut it into 2 equal pieces or 2cm each. Do not leave the skin on.
- Measure out 75 ml of hydrogen peroxide and tip it into the conical flask.
- Fill the ice cream container with water (roughly 3/4s full).
- Then fill the measuring cylinder right to the top with water and quickly put your hand over it so no water escapes.
- Take the measuring cylinder to the ice cream container and quickly turn upside down until the mouth of the cylinder is under the water. Make sure no air bubbles are in the tube to avoid unfair results.
- Put the 2 pieces of potato into the conical flask along with the 75ml of hydrogen peroxide. Quickly put the end of the delivery tube into the measuring cylinder in the ice cream container ensuring you don’t take the mouth of the cylinder out of the water, and put the bung in the mouth of the conical flask. Start the stopwatch at the point of input of the delivery tube. Let this reaction take place for 2 minutes then remove bung from the mouth of the conical flask.
- Once the 2 minutes is up, take the end of the delivery tube out of the measuring cylinder without taking the tube out of the container. Turn it upside down and mark on the water level with a pen. Then remove the cylinder from the water, turn it upright and record how many ml the water level decreased.
Diagram:
Measuring cylinder Delivery tube
Bung
Conical flask
Potato
Ice cream container
Prediction:
I think that the amount of oxygen given off from the reaction will increase as the concentration of hydrogen peroxide increases. I think this because the more hydrogen peroxide used, the more oxygen given off in the conical flask with the potato therefore more will be produced from the reaction. I think this because the higher the amount of molecules, more of the substrate is needed to break down the molecules.
Results:
Concentration Amount of 02 given off in 2 minutes (ml)
Of H202 solution
(%) 1 2 3 4 5 Average
= Anomolies
Analysis
A catalyst is a substance that lowers the activation energy required for a chemical reaction, and therefore increases the rate of reaction without being used up in the process. As can be seen from the graph, the prediction at the start of the plan was accurate; the rate of reaction did increase as the concentration of the hydrogen peroxide increased as the amount of oxygen evolved increased significantly.
By looking at my graph we can see that it is much a straight line with a dip at the end. We can see by the graph that the amount of oxygen goes up proportionally compared to the amount of potato/volume of hydrogen peroxide; because the part of the line is straight it means that the results can’t be exactly accurate. In addition to that my graph also did not match exactly the line of best fit.
My graph does not match the line of best fit. If I done my experiments correct; without any mistakes the lines should match exactly. I think this because the amount of enzymes will stay the same, however the amount of substrates changes. We were not allowed to add anymore catalyse else this would contradict the whole point of the experiment. But, we could change the amount of substrate by making the concentration of the hydrogen peroxide stronger, this means that eventually the amount of enzymes and substrate will equal each other out therefore forming a curve in the grap5h which levels off at the end.
I conclude that after looking at my graph and my results table it can show us the optimum amount of substrate and catalyse required is 2 pieces of potato and 75ml of hydrogen peroxide solution. For the best reaction you want as much hydrogen peroxide reacting with as much of the catalyse (in this case potato slices) and for that to happen the catalyse must have a large surface area.
I can back this up with my scientific knowledge. The two theories which can help here are the collision theory, which states if the more things collide the bigger the reaction. The other theory is the lock and key theory shows us how the enzymes make this reaction more violent. It is because the enzymes and proteins that act as a catalyse, so they speed up the reaction but are not used when it is finished. Lock and key theory shows us how they work as a catalyse.
The only other problems we could have had with the enzymes are if they had been denatured. This happens because they get too hot, and then change shape so the enzymes can’t react fully with each other. From past experiments and my scientific knowledge this fits in nicely with my prediction because I said that as long as the enzymes aren’t denatured and I set up the equipment efficiently I should get reliable results. My graph and results also backed up my prediction when I said I think that the amount of oxygen given off from the reaction will increase as the concentration of hydrogen peroxide increases. I think this because the more hydrogen peroxide used, the more oxygen given off in the conical flask with the potato therefore more will be produced from the reaction.
Rates of reaction = how many ml of 02 were given off per second. The trend shows that with the following concentrations, 5, 10, 15, 20 etc, the higher the concentration the more oxygen given off in two minutes. Also by the information I have collected, I can work out the rate of reaction.
Rate of reaction= volume of oxygen produced
Time
Average rate of reaction for 5% concentration=0.03 ml/sec
Average rate of reaction for 10% concentration=0.07 ml/sec
Average rate of reaction for 15% concentration=0.08 ml/sec
Average rate of reaction for 20% concentration=0.12 ml/sec
Average rate of reaction for 25% concentration=0.10 ml/sec
Evaluation:
The results did back up my prediction; the amount of O2 given off from the reaction will increase as the concentration of H2O2 increases. Our experiments went well and according to plan apart from a few problems we came across. One of the scenarios which could have caused the anomalies could be enzymes activity which varies with PH therefore the enzymes need a particular PH to work well. In addition to that the temperature may have had an affect on the results, but I very much doubt this as there was no sudden change at room temperature.
From our preliminary experiments we have learnt a lot about the odd results and how they occurred, we then interpreted this in our final experiments to ensure the same problems wouldn’t happen again; When we first tried out the experiment our bung didn’t fit into the conical flask properly therefore the oxygen escaped which caused an inaccurate result. But we changed the bung for our proper experiment. Another reason is because some delivery tubes were longer than others. This means the gas had further to travel causing the oxygen to take more time to travel into the measuring cylinder, therefore forming an inaccurate outcome. The only results that are anomalies are the ones highlighted in red on the results table. The rest of the results fitted into a pattern.
If I were to repeat a similar experiment again I could improve the way in which I carried out the experiment, for example, oxygen dissolves in water. This may mean that the bubble count measured is actually less because a small percentage of oxygen will dissolve directly into the water rather than from a bubble. An improvement on this would be to use another solvent, one of which oxygen does not dissolve e.g. petrol may give a more accurate reading. Using water would be a systematic error because the bubble count will be lowered for each experiment. I would do this experiment to increase my knowledge of how enzymes work and to create reliable, accurate results.
