Method
- Set the apparatus up as in the diagram.
- Half-fill the tub with water.
- Completely fill up a measuring cylinder with water and place it into the tub trying to prevent any water loss. Any water lost must be recorded.
- Cut out all the potato chips that will be used for the experiment using a cork-borer and then use a scalpel to accurately measure the chips are all the same size. Record the size of the potato chip used so that future chips will also be that size. Also record the size of the cork-borer used as this will affect the size of the chip aswell.
- Measure out the solution of water and hydrogen peroxide, 20cm³ of hydrogen peroxide at first and then minus 4cm³ of hydrogen peroxide and add 4cm³ of distilled water so that the concentration of the solution differs each experiment.
- Place this test tube in the clamp.
- Making sure the timer is ready place the potato chip into the solution, attaching the delivery tube straight after.
- As soon as the first bubble reaches the measuring cylinder start the stopwatch.
- Once the experiment has had 2 minutes reaction time, hastily take the measurement of oxygen in the measuring cylinder.
- If any, subtract the amount of water that was lost when filling up the measuring cylinder and record the result in a results table.
- Dispose of the used potato chip and repeat the experiment using different concentrations of hydrogen peroxide until 3 sets of results have been obtained.
The measurements of the potato chips must be recorded and a cork borer used to prevent the size and surface area of the chip from changing. The experiments will always be carried out at room temperature and the time allowed for the reaction will always be 2 minutes to ensure that the results remain accurate and reliable.
The only factor that is being varied in the method is the concentration and this should therefore be the only factor that varies the results thus giving relevant results to the investigation. Through only altering the concentration I should be able to draw a relevant conclusion as all results will be governed by the concentration of hydrogen peroxide affecting how enzymes in potatoes work.
To make the results reliable more than one set must be taken. I will range my results over 6 different concentrations and repeat the experiment 3 times, totalling 18 results. This is a suitable amount of results from which I will be able to calculate an average for each concentration. I chose this range as it will be sufficient for me to draw graphs from the information I collect and anomalies should be clearly seen whereas if few results were collected it would be harder to interpret which results were anomalous. This range of results should also allow me to clearly analyse the trends.
Results will be measured by filling a measuring cylinder with water and placing it into a water-filled tub. This will prevent the cylinder losing water and a delivery tube can be placed so that the gas delivered through will lower the water level. The measurement that needs to be taken is the amount that the water level has lowered over the 2 minute time period. I will account for any water lost before the gas has been delivered through by subtracting the amount the water level has lowered from the final result i.e. if 2cm³ of water was lost before the experiment and the final water level after 2 minutes reaction time was 6cm³ then the result would be 6cm³ – 2cm³ = 4cm³.
I predict that as the concentration of hydrogen peroxide increases the amount of gas produced will also increase. I think this because as the solution becomes more diluted there are less particles of reactant between the water molecules, which means collisions with the catalyse particles and hydrogen peroxide particles are less likely. Also, after researching from a textbook, I found that enzymes are also biological catalysts and speed up chemical and biological processes. This is because the particles stick to the surface of the catalyst where they react and if the concentration is increased then there are going to be more particles for the catalyst to react with thus speeding up the rate of reaction.
As catalyse is an enzyme the above statement should apply and therefore the rate of oxygen given off when the concentration is high should be greater than when the solution is more diluted and there are less reactant particles.
I carried out the method as I described in the planning section, however, in the planning section the method states that all the potato chips should be cut before the experiment and instead of this I chose to only cut two chips at a time because the chips were drying while the other experiments were being timed.
Results
Experiment 1
Experiment 2
Experiment 3
Averages
Identifying patterns in the results
The obvious pattern that the best fit lines show in all my graphs are that as the concentration of hydrogen peroxide increases the amount of gas produced also increases. I noticed that the extent of this increase is double and have drawn lines on all my graphs to illustrate that as the concentration of hydrogen peroxide doubles so too does the amount of gas produced i.e.- in experiment 1, when the concentration of hydrogen peroxide is 8vol. the amount of gas produced is 2.25cm³ and when the concentration is 16vol., the amount of gas has doubled to 4.5 cm³.
The reasoning for this can be seen with the predictions I made and explained in my planning section.
When looking at my results tables I also noticed that the amount of gas produced when the concentration of the hydrogen peroxide is 4vol. is on average 2cm and when the concentration is 16vol. is on average only 3.83cm and so this doesn’t support the doubling statement that could be taken from the graphs because the amount of gas produced has less that doubled, with only an increase of 1.83cm, even though the concentration of hydrogen peroxide has quadrupled.
This is due to me not being able to run the best-fit curves through all my results because even though the results are basically congregated along a straight line, giving reason for choosing linear best-fit lines, it was impossible to run them through all the results.
The results that are along way off the best-fit lines are likely to be anomalous results and I have circled these on my graphs.
After demonstrating that the result figures disagree with the doubling that the graphs show I still feel I can conclude that when the concentration of hydrogen peroxide is increased the amount of gas produced also increases. I can also conclude that when the concentration reaches a certain limit the extent of the increase in the amount of gas produced will slowly decline. However, I don’t think that the increase will ever completely stop because enzymes are a catalyst and catalysts cannot be used up and so the reaction will be continuous.
As I am able to draw these statements from my results, which fully supports my prediction, I am very confident with the results that I obtained.
Evaluating the evidence gained in the investigation
When carrying out the experiment I feel that the method used was very successful, discounting the minor alteration made to it concerning the amount of potato chips cut each time.
I was satisfied with the reliability of my results as they agree with my prediction and they were therefore what I was expecting. Although I think that my results are acceptable I could identify 3 anomalous results which can be easily seen when plotting the graphs. These results can be explained through minor errors when performing the experiment i.e. reading a result incorrectly from the measuring cylinder or inaccurately measuring out the solution.
In order to cancel out the erroneous results I would have to improve my method. One way this could be done would be to perform the experiment at the enzymes optimum temperature. All enzymes work best at their optimum temperature and so this would ensure that all the enzymes were reacting with the hydrogen peroxide as oppose to room temperature that could be slightly different from day depending on the weather outside.
A second improvement would be to use the same potato in all the experiments because different potatoes may contain more or less of the enzyme catalyse and according to which one it is there will me more or less catalyse molecules for the hydrogen peroxide to react with this will subsequently change the rate of reaction giving anomalous results.
Another improvement would be to increase the surface area of the chips. Having a small surface makes it difficault to tell the extent the concentration has on the amount of gas produced because the results will be lower and overall the range will be far shallower because in all experiments the rate of reaction will be low and the concentration wont have as great affect compared to having chips with large surface areas that should give higher and more importantly a wider range of results.
Making these alterations should help to gain more accurate and reliable results.
As mentioned earlier, I thought that my method was reliable because although improvements could be made, such as the ones above, the existing method was still adequate in giving concluding results and anomalies didn’t have a major affect on conclusions as they were ignored.
I feel that I have enough results to be able to produce strong conclusions because 3 results for each concentration are substantial as anomalies can be interpreted and averages calculated. Six different concentrations are also all that is necessary because trend lines and patterns can still be easily seen.
If I wanted to gain further evidence that an increase in the concentration of the reactant increases the amount of gas produced I could perform other investigations because all experiments should confirm this statement. This is because when the concentration is increased it just means there are more particles to react with and so there will be more collisions and this will speed up the rate of reaction.
Finally, I believe that the amount of evidence I provided is good enough to confirm my conclusion because the above theory, the conclusions drawn from my results and my prediction all agree that an increase in the concentration of hydrogen peroxide reacted with the enzymes in potatoes will increase the rate of reaction.
