Prediction (Hypothesis)
I predict that the more concentrated the hydrogen peroxide is, the faster the rate of reaction of the hydrogen and the catalase will be, and the faster the oxygen will being given off. Also the rate of the oxygen being given off should be directly proportional to the concentration of the hydrogen peroxide. I also think that the collision theory will also have an effect on the investigation due to the concentration of the hydrogen peroxide being increased. The collision theory is the theory that a chemical reaction can only occur between particles when they collide (hit each other). There is a minimum amount of energy which colliding particles need to react with each other. If the colliding particles have less than this minimum energy, then they just bounce off each other and there is no reaction. This minimum energy is called the activation energy.
Safety Precautions
Whilst performing the experiment, I will take into account some personal and public safety concerns. I will make sure that I wear safety goggles and wear a protective lab coat at all times so if, accidentally some hydrogen peroxide gets spilt or sprayed out I will not get it in my eyes, on my clothes or because will also have all my books off the table (apart from the results table, there will be no chemicals spilt on my books. I will be standing up so I can move out of the way quickly if necessary and the stools will be pushed underneath the desks and out of the way. I will tuck in any loose clothes, my tie, and I will take off my blazer. If there are any spills or breakages, I will inform my teacher immediately and get it cleaned up as quickly and as efficiently as possible.
Results Tables
100 % Concentration H2O2 Temperature of Water: 20°c 5ml H2O2 & 0ml H2O
80 % Concentration H2O2 Temperature of Water: 20°c 4ml H2O2 & 1ml H2O
60 % Concentration H2O2 Temperature of Water: 20°c 3ml H2O2 & 2ml H2O
40 % Concentration H2O2 Temperature of Water: 20°c 2ml H2O2 & 3ml H2O
20 % Concentration H2O2 Temperature of Water: 20°c 1ml H2O2 & 4ml H2O
00 % Concentration H2O2 Temperature of Water: 20°c 0ml H2O2 & 5ml H2O
Analysis
Through my investigation and through looking at my results I have found out that when a substrate’s concentration is increased, the rate of reaction of an enzyme medicated reaction increases. When H2O2 reacts with Catalase, oxygen is produced. The Hydrogen Peroxide has been broken down into oxygen and another bi-product, water. This is the chemical equation:
2H2O2 + Catalase → 2H2O + O2
From looking at my graph of the results I can see that between the concentrations the quicker the oxygen is produced and therefore, in a bigger quantity is produced in the time allotted for the experiment. From 00% concentration to 100% concentration the average rate of oxygen production ranged from 0ml to 3.3ml. Within any single concentration the only pattern I can identify is that of the amount of oxygen being produced. The amount increases in a pretty regular interval for each concentration.
The results that I am analysing agree with my prediction. My prediction, or hypothesis, stated that “the more concentrated the hydrogen peroxide is, the faster the rate of reaction of the hydrogen peroxide and the catalase will be, and the faster the oxygen will be given off. Also the rate of the oxygen being given off should be directly proportional to the concentration of the hydrogen peroxide.” The reaction rate did increase when the substrate concentration was increased, and the reaction rate did decrease when the substrate concentration was decreased.
This pattern can be explained by the collision theory. The more molecules there are which are able to react with a certain substance the quicker the reaction will occur. But only up to a certain point. This is shown where the concentration of the hydrogen peroxide is increased. The concentration is the amount of molecules per unit of the chemical, so therefore, the higher the concentration, the quicker the reaction and thus, more oxygen is produced in a shorter space of time. i.e. quicker.
Evaluation
The methods I used to carry out the experiment were fair and dependable, but only up to the point I could control. My measuring was as accurate as I could get it although had a calibrated, accurate measuring instrument been available to me, it would have made the measurement much more accurate. I made sure I read the volume of gas in the measuring cylinder, and the volume of the liquids in the pipette at eye level, taking into account the factor of the meniscus and I also cut the potato discs all the same, so they had the same surface area. The results I collected are still very accurate due to the amount of repeats. The multitude of results for each time and each concentration contribute to a very accurate average volume of oxygen produced.
On my graph of averages, when I plotted it I noticed that some results did not fit the pattern. These can be explained but, as there are many irregular results, one explanation of inaccuracy or mistake could cover all of the results. The largest irregularity is the whole of the 60% concentration average. The oxygen produced using this concentration was on average higher than the oxygen produced using an 80% concentration.
The reasons for the fluctuations in the results could be the product of many inaccuracies and reasons: I might have been slow in starting the timer: if so, the reaction would run longer than I wanted it to, producing an inaccurate result; there are no graduation markings on the from the bottom of the measuring cylinder to the marked, 1ml, therefore, making an accurate reading of the amount of oxygen produced, was very hard; whilst moving the reaction vessel into the water and under the measuring cylinder with my finger blocking the end of the delivery tube, I may have let some gas out accidentally, and this could give me an inaccurate reading of the amount of gas produced; I could have read the measuring cylinder graduations wrong during one part of the experiment; at the start of each day the hydrogen peroxide was made up fresh, by the lab staff and it was then left unused until it was used in a certain lesson during the day. Hydrogen peroxide breaks down naturally into water and oxygen in time, so if your lesson were at the end of the day, the concentration of the hydrogen peroxide would be weaker than the concentration at the beginning of the day. This will affect the results if on one day you had your lesson in first period, and then continued the experiment in the last lesson on the next day; I planned to use potato chips all from the same potato, for a fair test. But when there is a class of twenty all wanting to do this, it becomes impractical to have a potato and cork borer each. To avoid this problem, the lab staff bored cylinders from many potatoes and put them all in one big beaker and this prevented the use of one potato for each person. Therefore the catalase concentration may have changed throughout the investigation due to the different potatoes.
I can now critically analyse each step of my method to see why certain methods are not accurate and how these inaccuracies could be solved. I will start from the end of the experiment and move backwards: The experiments were conducted over at least four days and at different time of the day. This could not be helped due to the set academic timetable, and the times of the lessons. These reasons contributed to the varying concentrations of the hydrogen peroxide. This would have a very minor effect, barely visible in the results table but the effect is still there. This problem could be overcome by making a fresh concentration of hydrogen peroxide just before you are due to use it. The apparatus I used each day wasn’t the same. This hardly has an effect and it is scarcely visible in the results. The number of repeats of the experiment was limited due to the time limitation. And the less repeats you do, the less accurate the results become. To over come this, there could be one day a term set aside for scientific experiments, so there are virtually no limitations to the amount of results you can collect. Starting the electronic timer could have been the cause of many inaccuracies because of the time taken to place the reaction vessel under the measuring cylinder and then start the timer. The experiment could go on longer than desired and the results collected could be bigger than they actually are. Getting rid of this inaccuracy is pretty simple: get someone else to start the timer for you as soon as the reaction vessel is under the measuring cylinder. But doing this is also risky. There is a chance that gas could escape during the movement (either by my finger slipping, the reaction vessel knocking something or letting water into the vessel accidentally under water) and affect the results. To combat this I could have a larger trough with the apparatus in so there is nothing to knock against, but allowing water into the vessel is hard to prevent, I just have to be very careful not to let my finger slip. Whilst setting the measuring cylinder and the large beaker up full of water there were many errors I could have made. Filling the measuring cylinder up full, placing my finger over the end so as not to let any water overflow and then put it in the water and clamp it up is prone to errors such as: just letting a tiny bit of water out can cause the measuring cylinder to have some air in it, and this will add on to the total amount of oxygen produced. Making this error free would be simpler with a very large tank of water, so I could submerge the apparatus to fill them with water and set the measuring cylinder up on the clamp easier. Measuring the volumes of H2O2 and H2O accurately was not hard, as the pipette was graduated in ml. During the cutting of the potato it was very hard to get the exact 1mm measurements using just a ruler and a scalpel. I cannot think of way to make the cutting much more accurate whilst using a scalpel, ruler and my eye.
The results generally back up the conclusion I wrote. It is proved by the results showing that when the concentration is increased, there is, on average a larger amount of oxygen produced in a certain amount of time.
There are a large number of improvements I could make taking into account all the errors I have shown above.
I could have extended my investigation by performing a number of things, including: increasing the number of concentrations I test, increasing the amount of repeats of each experiment, increasing the time that each experiment is allowed to run for and increasing the amount of times I take readings for one concentration. Incorporating all these into my experiment will help me to get a more reliable and more accurate set of experimental results.
