This is the equation:
2H2O2 --> 2H2O + O2
Hydrogen peroxide --> water + oxygen
Diagram:
Controlling variable:
Keep the amount of hydrogen peroxide the same - This is so that the amount of catalysts working on the potato is the same each time.
Keep the samples from one potato only – So that you know there haven’t been different chemicals been used to grow the potato, therefore giving different results.
Keep the overall length of the potato the same – So that the surface area keeps the same on the outside. (But the surface area will change depending on how many pieces it is cut into.)
Use the same size boarder so that the diameter of the potato does not change.
Independent variable:
The surface area of the potato should be changed each time, this is done by cutting the potato into more pieces, and making sure the length of the potato stays constant. The potato should be cut into 1,2,3,4 and 5 pieces, and then placed into the hydrogen peroxide.
Fair test:
To make all my experiments fair I will use the same potato for the 5 different sizes of potato. Also I will use the same size borer so that the diameter will not change. I will use the same equipment so that the volume of the hydrogen peroxide will not change if the measuring equipment changes slightly.
Method:
First fill a 200ml beaker to about 100-125ml of water. Then take a burette and fill that full with water. Then place your thumb/finger over the top to prevent any water escaping. Tip the burette upside down and place into the 200ml beaker of water. Then get the delivery tube and place it inside the burette through the water, this is so that you can view the amount of oxygen given off by the potato reaction. Then get a cork borer and a potato and press firmly on the potato so you cut into the potato, then remove the potato from the inside of the borer. Cut up the potato into however many segments you will need.
Get a conical flask and fill it with 50ml of hydrogen peroxide. But the bung into the top of the conical flask and make sure the delivery tube is still inside of the burette. Then get a stop watch and as soon as you have placed the potato inside of the conical flask start timing for 5 minutes.
Results:
Experiment 1:
Experiment 2:
Experiment 3:
Conclusion:
I found out that my prediction proved correct, that when the surface area of the potato increases the amount of oxygen given off also increases. This is because the enzyme has an active site that helps it to recognise its substrate in a very specific way. Just like a key only fits into a specific lock, each enzyme has its own specific substrate. This is called the lock and key theory. This is why the oxygen is been given off, the hydrogen peroxide is the key and the potato is the lock, the hydrogen peroxide is been broken down inside of the key and oxygen is one of the elements produced.
With my experiment the potato where it is cut into 5 pieces I have 2 anomalous results where the reaction gave off the least oxygen then the rest of the potatoes. This meant I had to redo the experiment till I got the correct results, and to see if there was any pattern. On the graph I have completed I can see that there is a positive correlation, meaning that when the potatoes were cut up into more pieces more oxygen was given off. The graph I have plotted is for the average of all my results, so if there were any anomalous results they did not really show up on the graph.
Evaluation:
If I do another experiment, I would like to change it so the time on the potato being in the hydrogen peroxide increases; this is so I can get more accurate results, either that or I would cut the potato into more pieces to see a greater increase in oxygen been given off.
I think the experiment went very well, apart from the anomalous results. These anomalous results I had to correct by repeating the experiment, I don’t know why these results occurred, it could have been the fact that we used a new hydrogen peroxide solution, or just because the reaction didn’t work as well. Next time to improve the results I get I will use the same potato and the same hydrogen peroxide solution. With this experiment I found out that when the potatoes where cut into segments the hydrogen peroxide could work faster on them because there is more surface area to get to. From the results I gained you can see this pattern. I feel that I got a suitable range of results, because I was able to find a pattern in the experiment. The method I used meant sure that the experiment I carried out was safe and covered all the aspects needed to complete the experiment reliably.
I would have liked to find out other sources of reactants that could react with potato that gives off oxygen; this would have helped me to find out whether hydrogen peroxide is one of the main reactants that attacks the potato and gives off the most oxygen or whether it is the worst reactants.
