Here is a diagram of the apparatus that will be used in the experiment.
Here is a list of all the apparatus I will use:
Tile
Razor
Stop Clock
Boiling Tube
2 Hole Bung
Delivery Tube
Gas Burette
250ml Beaker
Syringe
Prediction
I believe that by reducing the concentration of H2O2 with water this will decrease the rate of decomposition of the H2O2, this is because the enzymes found in the potato chip are the catalysts and help the reaction to work and produce the water and oxygen. But when the concentration is reduced the enzymes will be finding fewer Hydrogen peroxide molecules so there will be less reactions taking place.
The rate of reaction will steadily get higher when more substrate is added because more of the active sites in the enzyme will be being used which will result in more reactions so the amount of O2 given off is higher. When the amount of substrate molecules added exceeds the amount of active sites there then the rate of reaction will stop going up. This is because the maximum number of reactions will be being done at once, so the other extra substrate molecules will have to wait until some of the active sites have become free.
Method
My method is as follows:
First I will assemble the apparatus as shown in the diagram, I will where goggles as I will be handling hydrogen peroxide. Then I will prepare the 1cm2 potato cubes and fill the beaker with water to cover the delivery tube. I will then fill the burette with water to the top and cover it with my finger, then place it in to the water.
The next thing I will do is putting the potato cubes in the boiling tube and covering it with the bung. I will draw up 5mls of hydrogen peroxide in to the syringe, then place the syringe in to the empty hole on the bung. Then I shall inject the hydrogen peroxide in to the boiling tube, but I must remember to leave the syringe in place.
After the air bubbles have come out I will quickly place the burette over the delivery tube and I will start the stop clock. Then when the water level has moved down 2cm cubed, I will stop the clock. Then I will record my results into a table and then I shall repeat steps 6 to 10 with the following regime:
Results
Graph
The graph of my results is on the next page.
Interpretation
From the results I have collected, I have now plotted a graph, showing the decomposition of the H2O2. If we look at this graph we can clearly see that points plotted on the graph are not that far away from the line of best fit, showing a quite strong relationship but a negative one. This means if we look at the graph, the lower the percentage of the concentration the longer it takes to produce 2 cm cubed of oxygen. Therefore the lower amount of hydrogen peroxide, the smaller amount of oxygen we are producing.
One enzyme can take on all the different molecules at the same time but only if they match the right part. This means that parts of the enzyme will only accept certain molecules for reacting with. In this case the enzymes take on the hydrogen peroxide (H2O2) molecules to make oxygen. As I kept the potato chip the same for the whole experiment the one thing that matters was the concentration of the hydrogen peroxide (H2O2) therefore as I predicted with the concentration at its highest I found it produced the most oxygen this is because there are more reactions happening and more collision and so there was a higher percentage of reactions.
The experiment proves my original prediction because from looking at the graph you can clearly see that as the mls of peroxide are decreased less oxygen is given off.
Evaluation
The data I collected was quite accurate, it was quite reliable meaning the results I collected was what I expected, but with contamination and human-error there were 2 slightly different results, which stood out a little from a exact pattern. But I added a line of best fit to my graph and everything came together and I managed to produce some basic conclusions but also the results were accurate enough to back up my prediction very well.
A slight cause for concern with accuracy was the measuring of the oxygen produced and also the measurements of hydrogen peroxide and water in the experiment. So if these inaccurate readings were carried out during the investigation then my results would be a lot different to what they should
Looking back on the experiment I think that there are a few ways to improve it. One of these would be the accuracy of the measuring of the potato cubes, if I was to do it again I would use an electronic ruler, with a digital screen that shows the length up to 3 decimal places. This would make every potato cube I use the exact same length and thickness. It was a little harder to measuring the oxygen given off. If I wanted to measure it more accurately it would involve using equipment that is not available to me and so cannot be carried out. The best way to take the readings accurately is to make sure that the same person reads it off incase someone else’s vision is not as good.
My graph was quite basic and one way to improve this would have been to increase the range off tests. I could have gone up to 10mls of hydrogen peroxide or gone down to 0.5 mls of hydrogen peroxide. This would have given me more results and when I would of came to plotting my graph there would have been more points producing a greater accuracy and a better line of best fit with which I would of been able to get stronger conclusions from.
To make the experiment as accurate as possible, I repeated it three times and used the averages of all the results to plot a graph with a line of best fit. I did my best to keep all the variables apart from the one I was testing (Hydrogen Peroxide) the same.
However in practice it is impossible to do using the basic apparatus. For example:
It is impossible to precisely measure out the exact amounts of Hydrogen Peroxide and Distilled Water each time, as the scale on the measuring cylinder only shows the measurement to the nearest 1mm cubed.
I think my timing was as accurate and reliable as it could have been, but only a forth or fifth experiment would back that up fully. The equipment we used was reasonable but not the best, but considering the conditions we were based in, it was the best we could of got, I also think contamination was minor so that would have not caused a problem.
