I will be doing 3 attempts for this experiment, which gives a total of 15 tests (5 in each attempt) I am repeating them because I believe by doing so I can obtain more reliable and accurate results. It will also be easier for people to read my graph because I now have more results to plot.
The cork borer, concentration of the hydrogen peroxide, temperature and pH should be kept the same so the results will not be bias.
I know hydrogen peroxide is powerful bleach and it is also corrosive. Therefore I will wear goggles throughout the experiment and I should treat the waste products safely.
I will be using the examples from the back of my textbook (Nelson Modular Science) and the mark scheme to help in planning and carrying out my investigation.
Diagram
Method
- Prepare 5 potato rods using a cork borer, which is 0.7 cm in diameter.
- Leaving one potato as it is, cut the other 4 pieces into halves, thirds, quarters and fifths.
- Fill the boiling tube with 10ml of hydrogen peroxide.
- Drop the potato rod that hasn’t been cut into the hydrogen peroxide.
- Start the stopwatch
- Measure how long it takes for the liquid in the manometer to move up 10cm.
- Repeat step 3 to step 6 again for 4 times, but using a different potato with a different surface area each time (e.g. the potato that was cut in half)
- Repeat the whole experiment (Step 1 to step 7) for 2 more time in order to get more results and make this investigation not to be biased.
List of apparatus
- Clamp and stand
- Boiling tube holder
- 15 boiling tubes
- Manometer
- Stopwatch
- Chopping board
- Glass measuring cylinder
- Thermometer
- 22.5 grams of potato (15 potato rods, each weight 1.5g)
- Fish tank
- Cork Borer
- Razor blade
- 150 ml of Hydrogen peroxide
- Pipette
Obtaining
- Accuracy, reliability and precision
Accuracy is very important in every experiment because after all the purpose of conducting an experiment is to find out answers which is provable based on knowledge with accuracy. In addition, I believe my investigation is very reliable because the set up of it is very simple, other students can simply follow my method and they should be able to repeat my investigation quite easily. Also, I have used a manometer for measuring the distance the liquid has travelled. A manometer is a reliable device which allows me to monitor the oxygen production and movement carefully, so I can record the results with great accuracy. I will measure the time taken with a stopwatch because it is very reliable and it is simple to use and most importantly, it is very accurate.
Here are the results I obtained from my first attempt of finding out the time taken for the liquid to move up 10cm in the manometer.
Table 1: Time taken for the liquid to move up 10cm in the manometer.
1st attempt
I then repeated the experiment for 2 more times so I can get more results for analysis. These 2 repeated tests would be done in exactly the same way as the first one.
2nd attempt
3rd attempt
In all three of the tables I have recorded the time taken for the liquid to move up 10cm from each test (to 2 significant figures)
Analysis
In order to find what is the total surface area of my potato rods. I have worked out a formula that can calculate the total surface area of them:
(Radius of a potato rod = 0.35cm)
(Length of the potato rod = 3.6cm)
(2 + 2n) x (Π x 0.35 2) + (Π x 0.7 x 3.6)
* n = Number of time(s) the potato rod has been cut
In order to convert the time taken for a reaction into the rate of reaction, I must first calculate the mean time by adding up the total time taken from all 3 attempts and then divide it by 3.
For example, the time I got for Test 1 was 42 seconds, Test 2 was 41 seconds and Test 3 was 38 seconds. I add them up and they give a total of 121. Then I will divide 121 by 3, the number of time I have attempted. This gives a result of 40.33 (2 d.p.).
(42+41+38) ÷ 3 = 40.33 seconds (2 d.p.)
Formula for the mean time:
(1st attempt’s time + 2nd attempt’s time + 3rd attempt’s time) ÷ 3 = Mean time
After I have done the calculations from above, I will divide 10cm by the mean time form each attempt so I can find out the rate of reaction. The rate of reaction tells us how many centimeters has the liquid moved per second in average during each attempt.
Formula for the mean rate of reaction:
10cm ÷ Mean time = Mean rate of reaction
Example:
10cm ÷ 40.33 = 0.248 cm/second (3 d.p.)
I have calculated the mean rate of reaction to the nearest 3 decimal places because by doing so, I will be able to get more precise results and therefore my conclusion will be more reliable and also my graph can be drawn with a greater accuracy.
Table 2: Table that shows the different surface areas and time taken for the liquid to move up 10cm in the manometer.
From my graph I can see that the mean rate of reaction was increasing slowly at the beginning and it gradually speeded up when the potato rods were cut more. I have calculated the gradients for 3 parts of my graph (Labelled A, B and C) I have found out the gradients are gradually increasing along with the increasing surface areas. At the beginning the gradient is 0.55, it rises to 1.29 then it goes even higher later on, to 2.78. The greater the number is, the faster the rate of reaction.
Formula which is used to find out the gradient:
Change in y direction ÷ Change in x direction = Gradient
I predicted the time needed to for the liquid to move up 10cm in the manometer would be shortened along with the increase of cuts. It was because when the potato was split into smaller forms and they gave a larger surface area. As a result, the rate of reaction was increased. As shown in table 2, the results (Mean rate of reaction) match my prediction. The rate increased from 0.248 cm/second to 0.698 cm/second, it was almost 3 times faster than the original rate. I believe the reason why the rate of reaction had increased so rapidly was because the greater surface area would increase the collision between the catalase and the hydrogen peroxide. Also, I had observed more oxygen was released as the total surface area was increased because there were more reactions taking place at the same time. To conclude, the larger the surface area compared to the volume, the faster a reaction can take place, as more simultaneous reactions can occur. As a result, there will be a faster rate of reaction, which will then produce more oxygen in a short period of time.
Evaluation
I think my investigation of how surface area would affect the rate of reaction went quite well. I obtained a lot of reliable and accurate results through careful planning and repeating experiments. Yet, although I had done all those preparations to avoid errors, I still got some results which are anomalous (Results which are highlighted in red from table 2) I think the reason of why they have slightly longer times was because I had used a new potato for my last 3 tests in my 3rd attempt. I was forced to use a new potato because I had run out of potato after my 2nd test in my 3rd attempt. Although they are the same variety of potato, the new potato was in a cooler temperature because it had been kept in the fridge. In addition, I had tried to keep every other factor that would affect the results (including temperature) constant. So by using a slightly cooler potato, my last 3 results were affected and they had had slower reactions with the hydrogen peroxide. I believe the reason why they reacted slower was because there was less kinetic energy for the molecules of enzyme to collide.
I think my range of result was quite wide already because I had done all together 15 tests (these are 5 tests for the time recorded from different surface areas and 3 more repetitions for each surface area) However, if I had more time, I would have gone even further in order to find out what is the greatest surface area I can produce and the time it would take to produce enough gas to push the liquid up 10cm in the manometer. My graph shows the rate of reaction was going faster and faster as the surface area of the potato was increasing and I would like to find out what is the greatest speed the reaction can give by continuing my investigation.
I believe the results I obtained are very reliable since the set up of my experiment was very simple and errors should have been avoided if I had fully followed my plan. I think I can improve my experiment in several ways.
Measurement of my result:
I believe I could have gained more accurate results if I was using a finer manometer. It is because with a finer tube, the movement of the liquid will be faster and therefore the change of movement can be seen more easily (and the results can be recorded with a greater accuracy, thus it gives me more reliable results) So I will be using a finer manometer next time if I am going to repeat this investigation.
Potato:
The main reason of why I have got some anomalous results was because I changed my potato at later part of my investigation. So next time if I am going to do the same investigation again, I will prepare a larger potato for it and so it will give me more of the same potato for testing.
The main reason of why the later part of my investigation (see the results which are highlighted in red in table 2) didn’t go as I had predicted was because I had used some new potato, which had a cooler temperature. Since temperature is an important factor that can vary the rate of reaction. I could extend the investigation by testing two potatoes that are in different temperature. This extended investigation can hopefully help me to understand more about the importance of temperature control and I can also research more on the knowledge about the rate of reaction, so next time I can plan my experiment more carefully.
For the experiment, I would set up 2 experiments in exactly the same way. One would be using a potato that is in room temperature (approx. 24 degrees Celsius) and the other one would be taken out from the fridge thus it would be cooler.
The experiments would be carried out just like I did before and the results will be measured with stopwatch. The manometer used this time will be finer than my previous investigation so it can improve my accuracy in obtaining my results.
I predict the rate of reaction for the warmer potato would be faster because there would be more kinetic energy for the Catalase to collide with the hydrogen peroxide.
