I intend to vary the concentration of the hydrogen peroxide by changing the amount of water it is mixed with, so that for every five millilitres the amount of water will be either none, 1 ml, 2m, 3ml or 4ml to every 5ml/4ml/3ml/2ml/1ml of hydrogen peroxide.
I was unable to achieve any results as part of the preliminary experiment because the gas travelled too quickly down the burette, so in the real experiment I will have to time how long it takes to go to 5ml instead of 1 ml.
Reasons for a preliminary Experiment
We did a preliminary experiment because then we would be able to choose which results to use when we do the real experiment. It would also make us aware about which variables we could change and which variables we should keep the same for each set of information.
Improvements and changes
Next time that we do the experiment I would like to change the following:
- Make sure each potato is the same length (measure them using a ruler next time)
- Make sure each potato has no skin on it – some of the potatoes that we used had their skins still on, and we don’t know yet whether having their skins on makes a difference or not, so it would be better to leave them off.
- Repeat the experiment three times to make sure that the results are right, or as near right as possible.
Fair test:
In this experiment there should only be two changing variables: 1: Different concentrations of solution. 2: Changing weight of the potato samples. To keep these two variables the only variables in the experiment I must:
1: Keep the potato samples the same length. This is because if one potato sample is 1cm long and one is 3cm long then the 3cm long sample will have a larger surface area and will react much more quickly.
2: Use the same potato batch. This is because many factors due to the potato may affect the experiment. For example the age, species e.g. King Edward, size and any imperfections in the potato can be kept to a minimum.
3: Accurate amount of solution: More solution may affect the rate of reaction. To make the amount of solution placed in the test tube as accurate as possible a syringe will be used to measure out the exact amount needed.
4: Contamination: As each test tube is filled up with the different strength solutions the syringe which would measure the amount of solution placed in the test tube may become contaminated with different concentrations. To stop this the syringe must be washed every time they are used.
5: Average: To make the experiment as accurate as possible an average will be taken out of 3 results taken. Also any clearly anomalous results will be ignored.
6:Temperature: The temperature may affect the reliability of the experiment for example at extreme temperatures the cells of the potato may die and at less extreme temperatures the experiment may be speeded up. To keep this from happening all the time the experiment will happen at room temperature.
Prediction:
I think that the less concentrated the solution of H2O2 is, the longer it will take for 5ml of gas to be given off because there won’t be as many H2O2 molecules to collide with the catalyse on the potato, so it’ll take longer for the reaction to take place.
On a graph, as the concentration of H2O2 molecules is increased the rate of reaction will increase forming a positively correlated line, increasing in gradient as the catalase concentration increases.
Results
Analysis
My graph shows, that as my prediction suggested, the rate of reaction slows down as the concentration of acid goes down.
The graph to show the amount of oxygen produced over a period of time by the reaction between Catalase and Hydrogen Peroxide shows that, in general, as the concentration of catalase increases, the speed at which oxygen is given off also increases. This was due to the increasing amount of molecules of catalase enzyme breaking down the molecules of the hydrogen peroxide substrate. It did this because catalase is a breaking enzyme. Being a breaking enzyme, each catalase molecule acquired a molecule of hydrogen peroxide substrate on its active site. Here, the enzyme divided up the substrate into much smaller parts.
The shape of the graph to show the amount of oxygen produced over a period of time by the reaction between Catalase and Hydrogen Peroxide follows a continuous shape because the amount of oxygen produced increased in a nearly regular pattern.
The graph to compare the rate of reaction between catalase and hydrogen peroxide to the surface area of the catalase shows that, in general, as the concentration of the catalase increases, the rate of reaction between the catalase and the hydrogen peroxide increases. This was because there were more active sites on the catalase in contact with the hydrogen peroxide substrate. This meant an increase in reaction rate and was visible because the oxygen was produced a lot faster. The points on the graph followed a positive correlation showing that there was a general pattern. There was one very anomalous result for the point representing the 60% concentration rate of reaction. This could have been due to a variation in the type of chip, or due to a mistake in the reading of value, or the timing system.
Overall the results recorded and the graphs subsequently produced do mostly agree with the prediction I made. The more catalase used did speed up the reaction rate between the catalase and hydrogen peroxide.
Evaluation
I carried out the method I produced following all the fair testing points I made as well as all the safety precautions I listed. I used all the equipment I listed.
The method was carried out well and accurately. The majority of results agreed with my original prediction. The results all seemed to follow the same pattern. One anomalous result occurred in the graph I produced. These were probably due to reading errors or slight changes in the potato type used. Another possibility is that one sample may have contained more potato skin than the others. The skin may be a faster or slower working enzyme than the potato flesh. The other factor that may have affected the experiment is the accidental release of oxygen bubbles or samples of either substance. I could have ensured more accurate results by using more accurate equipment, such as a more exact ruler or a micrometer, or the measuring cylinder that would have been more accurate had been a lot thinner (a burette).
There was sufficient evidence from the testing I carried out to support my conclusion because the results I obtained were enough to agree with my original prediction. I could have continued testing different variables, which would have proved or disproved my prediction correct. Further work to reach a better conclusion may be to research into more scientific theories and carry out experiments repeatedly until an accurate set of averages is achieved. If all the independent variables were experimented with as dependant variables then a nearly perfect conclusion could be drawn.
I think that my method for finding how the concentration of catalase affects the rate of the reaction between catalase and hydrogen peroxide was the best possible one under school laboratory conditions.