Prediction
I would expect from this reaction between the hydrogen peroxide and the catalase enzyme in the potato that the quickest and most reacted concentration of hydrogen peroxide would be the 50%. I would then expect 40%, 30%, and 20% and then the slowest to react would be the 10% concentration.
I would expect 50% to react quickest because it has the most Hydrogen Peroxide molecules in it. This means that a reaction is more likely to take place, in a shorter time, making the rate of reaction quicker. The more reactions that take place increases the amount of oxygen produced in the shortest time. The orders of reaction starting with the fastest are as follows: 50%, 40%, 30%, 20% and 10%.
catalase
Hydrogen Peroxide ------→ Oxygen + water
2H2O2 ------→ O + H2O
Safety
For this test I will have to make sure everything is done with safety and fairness. Throughout the whole experiment safety glasses must be worn, as Hydrogen Peroxide can be dangerous if it gets into your eyes. All other Lab rules must be followed also. To make sure the experiment is fair I must make sure nothing is changed for different experiments.
Fair Test
I will use the same apparatus for each different experiment and I will make sure the same types of potato and Hydrogen Peroxide are used. Everything in the experiment should be kept the same apart from the concentration of the Hydrogen Peroxide. Each time the potato will be replaced with another 5g of potato, as it will have been used to react with the Hydrogen Peroxide in the experiment before. All measurements of potato will be made to 2d.p. This will increase accuracy.
Method
I will then get the equipment I need for the experiment. I will then get 5g of potato will be measured out on the electric scales, this will be measured to 2 decimal places. This is accurate enough for the experiment I will do. I will fill the basin with water next and then fill the measuring cylinder as well. The measuring cylinder will be placed upside down in the basin still full of water, making sure that no water is escapes so that the experiment is fair. I will then put the potato pieces in the boiling tube. The next thing that must be done is to put the delivery tube and bee hive shelf together and place the delivery tube under the measuring cylinder so that any gas pushed through will go into the measuring tube. I will then make up different strengths of Hydrogen Peroxide solutions, which will be measured out using a small measuring cylinder; these concentrations are shown in the table below;
Concentration volume of stock volume of de-
Of H2O2 H2O2/CM3 ionised water cm3
10% 2 18
20% 4 16
30% 6 14
40% 8 12
50% 10 10
I will then add these concentrations in with the potato and the stopwatch will be started. Measurements will be taken from the side of the measuring cylinder every 30 seconds and noted down. Then I will note the end mass of the potato using the same mass balance to 2 D.P. All measurements will be made as precise as possible to keep the experiment accurate and fair. This will be repeated three times with each concentration so we may find a more accurate set of results.
Diagram
Results
The results I gained from the experiment are shown in the tables over the page, as well as the graph. The first show all the results for each experiment. The last shows the average figures from all of the concentrations.
Conclusion
From the results that I have obtained I can see a trend that has appeared. They show me that the higher the concentration of a substrate, the quicker the reaction rates of that substrate and the enzyme working on it. However there were a few results, which did not follow any of these results, these outlier results were ignored from my graphs as they would through off the lines of the graph.
The 40% concentration produced the most 0xygen in the shortest time, which gives it a higher reaction rate than the others; this is because any concentration over 40% poisons the potato. This shows that my prediction was almost correct; the 2nd highest concentration would produce the most 0xygen in the shortest time. The next highest reaction rate is the 50% concentration, this is because it is a higher concentration but it poisoned some of the potato. The results then show that in order the reaction rate gets lower as each concentration gets lower. My graphs also show that the reaction rate for 40% concentration is quickest because its line is steepest therefore it shows once again that more Oxygen was produced in a shorter time. I think that my results from this experiment were quite reliable and I have kept the non-variables as close to what they should be as was possible.
Evaluation
From my results I have found that the higher the concentration of Hydrogen Peroxide, the quicker the reaction rates, producing oxygen. I have succeeded in what I planned to do, which was to find out how the concentration of H2O affects the amount of oxygen produced in an enzyme catalysed reaction. The results I wrote down were what I had expected and predicted. An inaccuracy is when the experiment was started; the measuring cylinder may have still had some air bubbles inside it. This makes the results slightly less accurate. Another thing is that when the potato and the Hydrogen Peroxide were put into the boiling tube, they may have mixed slightly causing some oxygen to be lost.
I feel my experiment was a good procedure to use because it gave good results that were similar to what I had expected. The temperature was not the same on both days so this may have changed the results slightly. The enzymes may have denatured in some experiments because of the potato being exposed to the air, some people may not have sealed the boiling tube properly. Also more substrate concentrations could have been used to prove the whole experiment was correct. Another thing to be done would be to do more repeats for each concentration; this would make results more accurate when finding averages. This experiment could also be done the same except changing something else each time, like the amount of potato, keeping the same concentration of the substrate.