Surface area of potato As the surface area increases the reactions will increase because reactions take place in the surface. So there are more enzymes in the surface, making the reactions faster as they collide with the substrate.
Plan/Method:
Our coursework is based on a simple reaction between a solution of hydrogen peroxide water and a catalase. This can be shown in an equation:
Catalyse
----->
2 H2O2 2H2O + O2
Where hydrogen peroxide water has reacted with the catalyst and this is what it produces, water and oxygen.
I think that the variable which will most affect the experiment’s results will be the concentration of the substrate, in this case H2O2. I will make my experiment in the same room, that way I will keep variables the same such as temperature, surface area of the potato and pH. I hope the temperature in the room does not change, so that way our experiment will be fairer.
We carried out a trial experiment before we did the real experiment. We only used one solution and we only used one test tube, test tube holders, a knife, a cylindrical cutter, a stop watch and 10 ml of hydrogen peroxide which we mixed with water, so it was a 20 % concentration. We used 10 potato chips of 1mm width. We only used one concentration because we noticed that when we put in the catalase into the hydrogen peroxide in the test tube, there were too many oxygen bubbles coming out which we could not record and if the least concentrated solution could not be recorded then the rest could not be recorded either. We realised we had to change the experiment set up. The O2 showed the rate of reaction and we had to count the bubbles if we wanted to find out this rate and record it into a table. So we went on to setting up a more efficient experiment which would allow us to get some strong results.
In our second trial we also used one concentration and 10 potato chips. We mixed the solution using one test tube, a tube rack, a measuring cylinder, a beaker, a clamp-stand, a scalpel, a potato, a cork borer, a ceramic tile, a stopwatch, 4 pairs of goggles, a bottle of Hydrogen Peroxide, a tube rack, a spatula, clining film and silicon. As we saw that the experiment worked with one solution we proceeded to continue with the real experiment.
The set up of this experiment took us some time because we had to prepare a set of solutions. There were five solutions which each had a certain amount of hydrogen peroxide a: 20%, 40%, 60%, 80%, and 100%. This way the 20 % solution will be mixed up with 80 % of water, the 40 % one will have 60 % of water, the 60 % will have 40 % of water, the 80 % one will have 20 % of water and the 100 % one will have no water. I will use these concentrations, because they are equally dispersed and so I will see the gradual change in between them, that way I will compare the amount of water and oxygen produced in each one. We will cut all the potatoes with the same cork borer size, cut them by measuring them with a ruler and we will place the potatoes in clining film to conserve them while are doing the experiment, to make it a fair test. The potatoes will be dropped with a spatula in the hydrogen peroxide rapidly and the bung will be closed tightly, so that no oxygen can escape. It will be tricky to place the bung into the water and up the measuring cylinder very quickly as to not loose any of the oxygen produced in the first few seconds. We will put some silicon in the test tube and put a stand holding the cylinder to try and solve the problem, and another to hold the test tube where the H2O2 and potato chips are; which contain the enzymes used to catalyse the H2O2 to help produce the oxygen a lot quicker. We will fill up the beaker with water so oxygen will not escape. We used the water in the measuring cylinder to measure the overall amount of oxygen produced by seeing how much the oxygen has been trespassed from the test tube with the catalyse to the measuring cylinder.
Here we can see a diagram representing our experiment. The only thing missing are the two clamp stands which would hold the measuring cylinder and the test tube
To collect our data we will be measuring the amount of oxygen produced from the reaction, by letting it pass through a tube and let it go up the measuring cylinder, which will have water up to 10ml³, that way we can start to read our results because if we had started at 0ml³ the lines were difficult to read. Then every 30 seconds we will see how much oxygen has got up to the surface and so we will record it. Then we will put our results into a line graph. However when a period of 300 seconds have passed we will remove the tube from the cylinder and start the same procedure with another solution. I am going to use 5 minutes of time so that it was enough time to get the reaction going. The water produced by the reaction will stay in the boiling tube and only the oxygen will pass through the tube and reach the surface at the top of the bottom of the measuring cylinder. I knew my results were reliable because I saw that as the concentration increased the rate of reaction grew tremendously. The experiment was done two times, one done at 7ºC and another one at 17ºC and the 17 ºC one had a bigger rate of reaction than the one at 7ºC. We did this so that we could compare our results and see if temperature really affected the experiment.
To guarantee full safety of this experiment we had to look at what we were doing and see how we could things be safer. Because we were using H2O2 eye protection was important and so we had to put on goggles because any contact with eye could have caused serious damage. Also we had to make sure the cork bora and scalpel were used on a tile and not on our hands when cutting the paper. We placed all books, pencil cases, chairs under the tables and stood up during all the experiment. We will also use a lab coat.
To make it a fair test I will only change one variable that is the H2O2. I will make my experiment in the same room to not change the room. I will keep the 7ºC degrees concentration in the fridge. I will use the same type of potato so that genetic material is the same, and the same volume for each solution, 10 ml. I will use the same cork bora and the same measurements for each potato. I will wrap the potatoes in clining film so they keep fresh and conserved during the experiment.
Conclusion
Volume of oxygen produced every 30 seconds at each different concentration:
My results at first seemed quite high, and so I tried to plot them on a line graph to see if my results were really reliable. I made a line of best fit out of every concentration and made also a line equation for each one of them.
In each of these lines I could see a line equation and a number for R². I investigated it and I finally worked out that the value of R² showed us the reliability of the results. If it was between 0.7 and 1 it was very reliable, any equations out of these boundaries could be looked at as anomalies or outlions. All of my lines were in between these margins and they were quite near one which means they were reliable.
Then I saw I could also calculate the rate of reaction by looking at the line equation, for example: y= 0.028x + 2.0333. This means that for every second 0.028 ml of oxygen was produced.
Reliability of results
7ºC 17ºC
20% R²= 0.9602 20% R²=0.9661
40% R²=0.9666 40% R²=0.9433
60% R²=0.9717 60% R²=0.9677
80% R²=0.9897 80% R²=0.9907
100% R²=0.9932 100% R²=0.9916
Rate against concentration
7ºC 17ºC
20% R= 0.0128 20% R=0.0169
40% R= 0.0242 40% R=0.0294
60% R= 0.0202 60% R=0.0371
80% R= 0.0276 80% R=0.0449
100% R= 0.0280 100% R=0.0460
R= rate of reaction.
From the graphs I made I could see a general trend. As time passes the level of oxygen given out increases. As well as when the H2O2 concentration increases the levels of oxygen given out increase. There were not any anomalies or outlions I could comment on.
All my results did make sense and so I tried linking them to all the theories I could think about. By mixing the concentration of H2O2 with water this will decrease the rate of reaction This is because the enzymes found in the potato chip which are the catalyse produce water and oxygen and as I mentioned in the formula above because water molecules are now in there as well, the enzymes are colliding with fewer Hydrogen peroxide molecules so there are less reactions taking place. So 20 % concentration will give less oxygen than the 40 % one as it shown in the graphs.
As I did explain in my prediction enzymes are important to make a reaction work. An enzyme is a biological catalyst, each enzyme is specific which means that only the right shape and size of a chemical molecule will be able to fit in and be able to let the enzyme help with the reaction. This is also known as the lock and key principle, it must be the right shape and size other wise the enzyme cannot take control of the molecule and help it to change into something else.
Enzymes require a very special atmosphere; a steady temperature at 37, food and oxygen which is all they need, but if one of these factors stops or changes it can it can change our results because the enzymes would stop working and start to die, this would have a major effect on our experiment.
Anyhow as the temperature increases collisions will increase because particles move faster and so more enzymes join the substrate to form new products, that is why in my 17ºC degree graph results are much higher. The more energy produced the more oxygen will be given out. If the temperature increases the kinetic energy will speed the reaction.
To get better results we could have increased the amount of hydrogen peroxide, making it a 110 % solution, which would then give us more reactions and better results. I also tried and instead of making a lineal line of best fit I tried to make a potential one, because a lineal equation would mean that as time passes reactions will still take place and the amount of oxygen will increase. A potential line of best fit will show us that after a certain period of time how the reactions will stop taking place. But because we did not proceed to record our results further than 5 minutes after we put the potatoes in the H2O2, it is useless to do this.
Evaluation
My experiment has been carried out successfully, but it could have been done much better. Throughout the experiment I have been annotating any forms in which I could have improved my work. The results I got were the ones I expected to get. So my experiment has effectively matched my prediction.
During the experiment I saw how some things went wrong and so then I tried to find a solution to most of them. In the first place, when we wrote down our results every 30 seconds, we might have read them wrong. So then the results would be slightly wrong and they would be carried across all the experiment affecting our final results. But unfortunely we did not have equipment to solve this and we just had to look at it and record it. The hydrogen peroxide could have also been put in a water bath while doing the experiment so there were not any changes and the temperature could remain the same. We could have also made more readings, and so we would have gotten more results to plot on our graphs. Maybe doing 9 H2O2+ 1H2O, 8H2O2 + 2H2O, etc. Or even with decimal places, 9.5 H2O2 + 0.5H2O, 8.5 H2O2 + 1.5H2O, etc. We also could have changed other variables like the surface area of the potatoes by cutting them in smaller peaces, so then we could compare results. Another problem was placing the bung inside the test tube. When we tried to put the bung inside the test tube after a few seconds it automatically came out and so in some of the concentrations we had to push it during five minutes, so that means that more pressure was being made and so more oxygen would be given out. When we cut the potatoes we could have done it with an electronic ruler which would have given us up to three decimal places. The clining film was not very good and it braked easily so when we opened it to get some potato slices we had to use more clining film. Another problem is that there were not enough clamp stands to hold the test tubes and so we had to use one for the test tube but we could not use one for the measuring cylinder.
Well on the whole the experiment ran smoothly, the equipment we used was not necessarily very good but considering what the school had I think it was the best material in the school.
