In my experiment I will be looking at temperature and how it affects the rate in the reaction. Enzymes work best at their optimum temperature, if the temperature goes above this the enzymes begin to denature. When an enzyme denatures it is because the heat can disrupt the bonds in the proteins primary, secondary and tertiary structures, by causing the atoms to vibrate out of shape from an increase in energy. The heat causes this. Once the enzymes are vibrating the ‘lock and key’ method will not work until the enzymes are cooled enough to stop vibrating. If the temperature increases too much eventually the enzymes will break the bond and return form the tertiary structure (which all enzymes are) to the primary structure. If the temperature is being increased to the optimum temperature then the enzymes will have more energy causing them to move about more and this will result in an increase in collisions. Which in turn will end up with an increase in the reaction.
As well as changing the temperature other possible variables that could be changed are: potato mass, the greater the mass the more enzymes. Potato surface are, if the potato has a greater surface area but the same mass more enzymes will come into contact with the hydrogen peroxide and therefore more successful collisions. And volume of hydrogen peroxide, if there is less hydrogen peroxide the enzymes will have less work to do with the same number of enzymes so therefore the speed of the total reaction will be increased. I have decided to look at temperature so all other variables must be kept the same to keep the test fair.
I will do a preliminary experiment to find out which equipment will work best to measure the amount of oxygen gas given off (this is how I will work out the rate of the reaction). Once I have got the right equipment I shall make sure for the actual experiment I do two repeats so that any anomalous results will be spotted. This will also make sure that my results are accurate.
I am going to use as close as I can get to 3 grams of potato and 20 to 30ml of hydrogen peroxide, I haven’t decided on the exact amount yet. My experiment will last for four to five minutes taking readings every thirty seconds.
Prediction
I predict that with an increase in temperature the rate of reaction will also increase, until I reach the optimum temperature then the rate will slow until the reaction will no occur at all. This is because with an increase in temperature the enzymes will have more energy and more about faster causing more reacting collisions. Once the temperature goes above the optimum temperature the enzymes begin to denature. When an enzyme denatures the heat disrupts the bonds in the proteins by causing the atoms to vibrate out of shape from an increase in energy. If the temperature increases too much eventually the enzymes will break the bond and return form the tertiary structure to the primary structure. The heat causes this.
However this will only happen if there is an excess of substrate if there isn’t, then the reaction will stop when all the hydrogen peroxide has been used up, in the time allowed. So that at the optimum temperature the reaction will take the same amount of time as when the temperature is just less. I have drawn two diagrams to illustrate this.
With an excess without an
of substrate. excess of substrate
Preliminary experiment
I did two experiments for my preliminary, the second was much more successful than the first. I shall use the equipment that I used in my second experiment for my investigation. Below are the two diagrams for each experiment:
First experiment
Starting mass of potato: 2.9g Starting volume of hydrogen peroxide: 30ml
Second experiment
Starting mass of potato: 3g Starting volume of hydrogen peroxide: 25ml
Starting temperature: 25° Finishing temperature: 27°
The first one went wrong and the results weren’t very useful. I did the experiment for four minutes and took readings every thirty seconds and the second was the same except it lasted for five minutes. Here are my results to show how much better the second experiment worked.
Apparatus
- Water tank
- 25ml measuring cylinder (two)
- Clamp and stand
- Boiling tube
- Boiling tube rack
- Delivery tube with bung
- Thermometer
- Stop watch
- Potato
- Scales
- Hydrogen peroxide
- Knife (to cut potato)
- Bunsen burner (to heat up hydrogen peroxide)
Diagram
Method
Set up the apparatus as shown in the diagram above. Place the measuring cylinder under water and fill it with water, so as gas goes into the cylinder you can see how much is collected by the level of water. Measure out 25ml of hydrogen peroxide and put into a boiling tube. Measure the temperature of the hydrogen peroxide and record it. Weigh out the potato and make sure it is at the right weight (3g) or as close as you can get, preferably 2.8g to 3.2g. Place the potato into the boiling tube with the hydrogen peroxide. As soon as the potato makes contact start timing. Take readings every thirty seconds, making sure you are on eye level as to get an accurate reading. At the end of the experiment again measure the temperature. Repeat the experiment but with an increase of temperature. To increase the temperature put the hydrogen peroxide into a Bunsen burner till you get the right temperature.
The first experiment will be at room temperature (around 25°). For the next ones start at 30° and go up five degrees each time to 50°. Each time use fresh potato and hydrogen peroxide. Make sure you are wearing goggles as to protect your eyes. Repeat the experiment at lest twice so that you can get accurate results. I have used 20 ml of hydrogen peroxide in this experiment not 25ml.
I will record my results in a table like the one below:
Results
I have done all my results to the nearest .25 of an ml, this is the most accurate I could get my results with the equipment I was using.
For the last repeats of 45° after the first three the results do not match the other two sets of results I have. These are all anomalous. Below is a table with the averages in and in that table I have not used from 2.5 to 5 minutes of 45°. On the graph I have plotted the anomalies though so you can see where the results have gone wrong. Also on the graph I have worked out the gradient of each line so that I could work out the rate of reaction, which is plotted on the next graph °. On the graph I have plotted the anomalies though so you can see where the results have gone wrong. Also on the graph I have worked out the gradient of each line so that I could work out the rate of reaction, which is plotted on the next graph with the temperatures.
Average results