I will be altering the concentration of the substrate. I predict therefore using my above knowledge that as the concentration increases the rate of reaction will increase as well. I believe that the graph I will produce will resemble this.
Volume of oxygen (cm3)
Time
I predict that the higher concentration will have a steeper line of best fit, compared to a lower concentration of hydrogen peroxide. I also believe that the line of best fit will not bottom out until more time has passed because there is more substrate to react with. Therefore, as I will only be measuring until five minutes, I expect catalase to be still present to react with the hydrogen peroxide. The lower concentration will be less steep because there is less substrate to react with. The rate of reaction will be quicker at the start because there will be a higher collision frequency, at the start then with the other concentration. I think that the line of best fit will go through the origin because always at zero seconds there will be zero cm3 of oxygen produced.
I will measure the time of reaction by measuring the amount of oxygen being produced by the experiment. To do this I will have to use a water bath and a measuring cylinder full of water. I have tried this already in a preliminary experiment to make sure my method is correct. I have to fill a measuring cylinder with water and place it into the water bath upside down so that the water level in the cylinder is now at zero. This makes it a fair test, if all the experiments I wish to conduct start at zero on the measuring cylinder. I then add the potato to the hydrogen peroxide that is in a boiling tube. Quickly I have to put the bung of the delivery tube onto the boiling tube and place the open end under the measuring cylinder in the water bath. This must be done quickly is that not much oxygen is used up, and not recorded.
I would also like to observe whether each bubble produced becomes smaller as the reaction occurs.
To make sure my test is safe, I have to but he boiling tube onto a rack, so that it does not drop off the bench. I also have to be careful using the scalpel and have a tile underneath the potato when cutting it, so that I do not leave any mark on the table. Therefore, it will work safely. To make it a fair test, I will have make sure the potato’s are of same size, and measure them to make sure. I now know that my plan is a fair test.
These are the results of my preliminary test. I used one potato and in one concentration, and I took reading for seven minutes. I have done this to create a reliable method that I can use in my real experiment.
Obtaining Evidence
Apparatus
-
25 cm3 measuring cylinder
-
50 cm3 measuring cylinder
- Boiling tubes
- Clamp
- Cork borer
- Delivery tube
- Distilled water
- Hydrogen Peroxide
- Potato
- Scalpel
- Stand
- Stopwatch
- Tile
- Water bath
Method
- Set up experiment as in diagram
- Use cork borer carefully, to cut out 5 equal potato tubes
- Fill water bath three quarters way up
- Fill measuring cylinder with water and place into the water bath, so that the water level is at zero on the measuring cylinder
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Put 40 cm3 of 40-volume hydrogen peroxide into boiling tube, use gloves when doing this because hydrogen peroxide is corrosive therefore will corrode the skin.
- Add potato, and quickly put bung of delivery tube onto the boiling tube and place the other end into the measuring cylinder in the water bath.
- Start stopwatch, and take reading every thirty seconds, and put results onto a table like the one below
- During one of the experiments take a glowing splint and see if it relights in the test tube where the gas in being given off. If it does then oxygen is being given off.
- Repeat steps five to seven with different concentrations of hydrogen peroxide as written in the table below.
Draw graphs and make conclusions
As you can see, I am controlling the temperature, as a constant. I have varied the pH level of the hydrogen peroxide and concentration purposely. However, this experiment I am concerned with varying concentration only.
I am going to keep on timing each experiment until the oxygen stops arriving at the measuring cylinder. I am going down in 25% parts of the hydrogen peroxide so my results can be easily seen in my graphs. I will repeat any results I think are bad, by repeating the whole row of results on the results table. I will do each concentration twice, to make sure my results are correct.
I have found after doing the experiment that you can only start the stop watch after the first bubble has arrived, because there is water left in the delivery tube, which slows down the time taken for the bubble to arrive.
I feel that repeating each concentration twice will give me a good set of results. I also think that I will record these results suitably using the above tables.
Results
As you can see, I have tabulated my results clearly.
I have repeated some of the results because I noticed some rogue points appearing. In addition, I have repeated each concentration twice so that I can average out any rouge points that I have not noticed already. This will help the accuracy of my results.
I feel that these are high quality results because they seem to agree with my plan, and hypothesis. I will now draw graphs to see whether my initial reactions to these results are correct. I feel I have made enough observations and measurements including repetitions to obtain reliable evidence. I am drawing a graph to see whether my results fit a certain trend, which I mentioned in my plan.
I will now make a table of averages, which will average out any rogue points in my results.
I will circle any anomalous points that I witness when I draw the graph.
Analysis
I can show what I found out using the graphs I have produced.
Along with the results shown I found that the gas given off was oxygen because a glowing splint was placed in the boiling tube and it relit.
I have drawn line diagrams to show my results. This is so that one can see the plots that concern my results and the line of best fit. I have circled any anomalies that I have witnessed on my graphs.
On the first graph, I have made four anomalous reading. The steepest line is the 20-volume hydrogen peroxide solution. This is not what I predicted, as I thought that the highest concentration of hydrogen peroxide would have the steepest line of best fit. All the points I have made are situated very close to the line of best fit, apart from the anomalous points. This shows that my results were accurately made. I also thought that the line of best fit would go through the origin, however all of the lines miss the origin by a small amount. The gentlest line of best fit was the 10-volume concentration, which was predicted. All the lines are in steepness order apart from the 20 volume, which seems to be an anomalous line because, if I take the other three lines they are in order of concentration when it comes to steepness. This could be due to a number of factors, which I will discuss in the evaluation. In two of the lines (40 volume and 30 volume) the last point is the same as the point before. This could be because the reaction rate had fallen and the next bubble was in the delivery tube about to come out when the five minutes was up. If this bubble had arrived in time, I am sure that the result would not be anomalous.
If you look at my second set of results, you can see that the lines of best fit are much nearer the origin in comparison with my first set of results. This is because I learned my mistakes from the first set of data. For example, I did not start the stopwatch until the first bubble arrived in the measuring cylinder. You can also see that the steepness of each results are in order of their concentrations. This implies that these results are more reliable then the first set because they agree with my based on fact hypothesis. There was one anomalous point in the whole of the second set of results, implying these are more reliable. The results are scattered very closely to the line of best fit showing I have made good results. However, they still do not go through the origin, which was what I predicted.
My average set of result therefore, do not seem to coincide with my hypothesis, because the first set of results seem to increase the results of the 20 volume hydrogen peroxide solution. There are two anomalous points in the average set of results graph. I feel that these could have been removed if I did the experiment one further time, but due to time restrictions, I could not. If you look back in my plan, I have showed the results of my preliminary experiment. I feel that a could have used my first set of results as a further preliminary set of results, because I learned more about the method that I should have used. The steepest line was the 40-volume concentration of hydrogen peroxide, which was what I had predicted. The steeper the line, the faster the reaction took place that is why I keep on referring to the steepness of the lines.
I also found that the reaction was more vigorous in the higher concentration of hydrogen peroxide then in the lower concentration. There were more bubbles formed in the boiling tube in the higher concentrations. In addition, the oxygen came out in bubbles, and in the higher concentration of hydrogen peroxide, these bubbles were bigger, and each one had a bigger volume.
My results have turned out this way because of the factors I have talked about it my plan. The fastest result was the 40-volume solution because there were more hydrogen peroxide molecules to react with the constant catalase enzyme. If you decrease the amount of hydrogen peroxide then there is less chance of there being a successful collision between a hydrogen peroxide molecule and catalase. I will explain this in diagrammatic form.
Hydrogen Peroxide
Catalase
As you can see, there are twice the number of hydrogen peroxide molecules in the first diagram compared to the second diagram. Therefore, there is twice the chance of a successful collision between these two molecules in the first diagram. I would also state that the reaction would go on longer, but have no proof of this. If I double the concentration of hydrogen peroxide, I would expect the reaction rate to double. In this case, again I could not measure this. The theory shown here is proved my results, because the steepest curve in my average set of results shows that the highest concentration has the steepest curve. It also shows that the lowest concentration has the gentlest curve. Thus, proving the theory.
If you look at my second set of results and to an extent the average set of results you can see that the results I have made support my prediction that as the concentration went up the rate would go up. Therefore as the concentration increases the rate of oxygen released increases, and we can see this by using the steepness of the lines. The gradients of the lines are as follows:
As you can see this agrees with my prediction that as the concentration increases the rate increases. The steepness of the curves provides the rate at which oxygen was released out of the potato. The rate is proportional to the concentration, however it is not, what I predicted it to be, because I predicted it to be directly proportional.
Evaluation
If you look at my results, you can see that there is small scatter around my line of best fit but more importantly, my results do not go through the origin as expected. This shows there were flaws in my method. My results however, do agree with my predictions, however they are not 100% accurate therefore there must be things that I need to change if I were to do the experiment again. I think this was due to insufficient time.
I feel that my results were accurate enough to form a firm conclusion, however some amendments to the method could be made to increase the accuracy and precision of the results.
If you look at my final graph you can see that thee are two anomalous points in the 30 volume and 20volume lines of best fit. I will now suggest improvements to my plan.
I would have measured the mass of the potato pieces so that I am sure that the potato pieces used are of the same mass, otherwise the test could become unfair, if the potato pieces may be the same size but one could be denser therefore containing more catalase enzyme. In addition, to be more accurate in my measuring callipers could be used so that I can measure the exact length of each potato piece.
I would have liked to use an instrument that would allow me to add the potato and quickly close bung. For example, a hole in the bung where you can add the potato and then rapidly replace the cap over the hole. I would also have liked to have a way of places the delivery tube inside the measuring cylinder in the water bath quickly, so that no oxygen is lost while doing this. In addition to this, water went into the tube while I was trying to get the delivery tube into the measuring cylinder. It took time for the first bubble to arrive. I think this could have hampered my results because there would be a bunch of bubbles together in the tube trying to push the water out, this would affect my results concerning the rate. I feel tat the water bath was too small, and a larger one would allow more room for the hand to reach under the measuring cylinder and insert the delivery tube.
To obtain further evidence I would allow the oxygen to completely stop coming out of the potato, so I can measure the rate better, and am able to recognise more points that are anomalous. This would give me further evidence and allow me to write a firmer conclusion.
To extend the investigation I would see how much affect the temperature and the surface area have on the rate of oxygen released. I would measure the temperature by having a heated water bath, which would keep the test tubes at constant temperature. I would use the same concentration of hydrogen peroxide along with potato pieces of the same mass and surface area, and place them in differing temperatures. I could then draw a graph of rate of reaction vs. temperature. To measure the surface area I could measure the surface of each potato piece using callipers and see whether different surface area of potato pieces in a constant concentration of hydrogen peroxide give different rates of reaction.