Prediction
I predict that increasing the surface area will increase the amount of exposed catalase. I would expect the number of oxygen bubbles per minute to increase which indicates an increase in the rate of enzyme action. WHY? Because there is more surface area, there would be more catalase therefore more active site combining with Hydrogen Peroxide at any one time and more oxygen bubbles being produced.
Constants
Throughout the experiment we are going to keep the pH, temperature of the room and solution, length of chips (5cm), volume of hydrogen peroxide, type of potato, volume of chip = 5x1x1 = 5cm constant
Variables
The independent variable: amount of enzyme exposed
The dependant variable: Number of oxygen bubbles per minute produced as hydrogen peroxide is split by catalase = faster reaction (rate of enzyme)
Preliminary experiment
Before I start the experiment, I am going to do a preliminary test to determine what length of chip I need to use to make it constant throughout the experiment. I also need to know how much hydrogen peroxide is needed – enough to cover the chip. For my preliminary test, I am going to use water instead of hydrogen peroxide to see how much I need to cover the chip. I have decided the length of the chip to be 5cm. I will place this in a measuring cylinder (accuracy) and fill the cylinder with water until it covers the chip. I have chosen 20ml of hydrogen peroxide.
1 piece:
sides
Surface area: (5x1) x4 = 20cm
Ends of the chip +1 + 1 = 22cm
Method
Before I begin the experiment, I will gather the apparatus that I need. I will select 6 potato chips and put them into a wet towel to keep it moisturised. I will do my preliminary test. I have decided to cut the potato chips to 5cm. I also need to know what volume of hydrogen peroxide I will need; therefore I will place a chip in a measuring cylinder and pour water instead of hydrogen peroxide into the cylinder until it covers the chip. I have decided to measure 20ml of hydrogen peroxide in a test tube. Before I start counting the bubbles I need to take the room temperature and note it down. Then I will fill a test tube with water. The bubbles will appear in this test tube and place it on a test tube rack along with a side arm test tube to hold it in place. A syringe is used to collect the 20ml of hydrogen peroxide. Once the hydrogen peroxide is collected I will place a chip that has been cut to 5cm into the side arm test tube and I will pour the hydrogen peroxide. The pH will be quickly taken by dropping the pH paper into the solution I will then immediately twist the bung carefully on the side arm test tube making sure it is air tight. The chip is left to equilibrate for 30 seconds. Then I will start the stopwatch and begin counting the bubbles for 5 minutes which will appear in the test tube filled with water.
Once the 5 minutes has ended, I will take the temperature of the solution. The hydrogen peroxide is poured down the sink and the chip is thrown into the bin but the water in the test tube can remain the same
Then I will take another chip measuring 5cm. This will be cut into half, placed on a tile and cut with a knife, which will increase the surface area which increases the amount of exposed enzyme but I have to make sure that I cut the chip vertically because if it is not vertical, the surface area would increase. Again I will take 20ml of hydrogen peroxide into a syringe. The chips will be placed in the side arm test tube and I will pour the hydrogen peroxide. Carefully the bung will be placed. It will equilibrate for 30 seconds and then I will start counting for 5 minutes.
The chip is then cut into 4 pieces and the same procedure is repeated. Then it will be cut into 8, 16, 32 pieces each time doubling its surface area.
The whole experiment is repeated again using another 6 potato chips cut into 2, 4, 8, 16, 32 pieces. This is to make my results accurate and also to find the number of oxygen bubbles per minute. Once I have found my overall results I will plot them on a graph.
A results table like the one below will be drawn up to write down my results in:
(i) (ii)
I have predicted that my graph will look like this:
Obtaining
Safety
We must wear an overall when doing this experiment so that the hydrogen peroxide does not come in contact with our clothes.
We must wear goggles because the hydrogen peroxide is very corrosive.
When we take the hydrogen peroxide into the syringe we must wear gloves and continue on wearing them during the experiment.
We must be careful when using the knife or scalper (to cut the chip) that we do not cut ourselves.
The apparatus must be in the middle of the table so it does not spill or knock over.
Results
A table to show the results of different pieces of the potato chip in 20ml of hydrogen peroxide.
Constants: Volume of hydrogen peroxide = 20cm
Volume of chip = 5x1x1= 5cm
Temperature of room at the beginning = 24
Temperature of the room at the end = 25
Temperature of solution with 2 pieces = 21
Temperature of solution with 8 pieces = 20
Temperature of solution with 32 pieces = 19
pH of solution with 2 pieces = pH 4 (yellow)
pH of solution with 32 pieces = pH 4 (yellow)
Analysis
My graph shows a linear relationship and a constant gradient.
Looking at my graph, I can say that an increase in the amount of enzyme affects the rate of enzyme action. At an area of 22cm the number of bubbles being produced was approximately 10.4 per minute, however, at 36cm the number of bubbles produced per minute was 18.8.
Looking from my graph, I predict that there would be approximately 11 bubbles being produced at 20cm and at 40cm there would be 22 bubbles being produced. If we double the area is it true that the bubbles double as well?
For example:
20cm = 11 bubbles
40cm = 22 bubbles
40cm = 22 bubbles
80cm = 44 bubbles
My prediction was proved correct, that increasing the surface area will increase the amount of exposed catalase therefore the number of oxygen bubbles will increase indicating an increase in the rate of enzyme action. This is what I suspected because if I increase the surface area, I am increasing the enzyme’s active site and so more hydrogen peroxide is split releasing more oxygen therefore more bubbles appearing.
This theory ties in well with the Collision Theory. That is for a reaction to take place, the particles of the substances that are reacting have to collide. If they collide, with enough energy then they will react. The minimum amount of kinetic (movement) energy that two particles need if they are going to react when they collide is called the activation energy.
There are therefore two main ways of increasing the rate of a reaction:
- Increase the number of collisions
-
Increase the amount of movement (kinetic) energy so that more collisions lead to a reaction.
Unlike my friend’s graphs, my graph seemed to produce a straight line but I was expecting a plateau because of many factors: the hydrogen peroxide eventually becomes limiting, there is an overlapping of chips and so less exposed surface area which means less oxygen bubbles, the froth produced will cut down the rate of oxygen bubbles.
I experienced a few errors in my experiment but it still produced a straight line graph with no anomalies in my graph and so my results are accurate but still can be improved.
Evaluation
Overall, my experiment was a success and I produced results that were satisfying. My prediction was proved correct that increasing the surface area will increase the amount of exposed catalase therefore the number of oxygen bubbles will increase indicating an increase in the rate of enzyme action.
Even though the experiment was probably not performed as accurately as it could have been because of some controllable and uncontrollable conditions, some mistakes can be corrected.
To improve the accuracy of my results, I could have found a way of collecting the volume of the oxygen produced and measuring that. Also I repeated my experiment twice but if I wanted to improve the reliability of my results, I could have repeated it 3 times but I was limited in time. I should have found a way to separate the pieces of potato because they would cling with each other.
The accuracy of my instruments needs to be improved also. I found it difficult drawing my line of best fit because my results were spread out and also the knife I was using to cut my potato chips with was blunt therefore some pieces might have been vertically cut without being realized. This would increase the surface area making it bigger and so it would not be a fair test.
During the experiment I experienced a lot of faults and errors.
It was difficult to count the number of bubbles and watch the stopwatch as well. Therefore I might have missed a number of bubbles or might have over counted some. When I was doing the experiment it was open day and so I got distracted by parents coming round to see the experiment. I estimated the equilibrate time and so I might have left it for too long or too less.
The experiment was unfair because the pressure on the force of the bung was different each time. I might have not tightened it enough and so it would be left loose. The temperature of the solution and room changed, I tried to keep the room temperature constant but it was impossible. The temperature went up by a few degrees which could have increased the enzyme action. Also when I cut the chips in pieces and placed them in the hydrogen peroxide, they would cling with each other and would not separate. This would make the surface area lessen.
I realized that fresh chips straight from the water seemed to work better than those that were left damp in wet tissue paper.