Aim:
My aim is to compare the reaction rates between crushed liver and crushed potato when placed in hydrogen peroxide through loss in mass and see which tissue cells contain the most catalase.
Hypothesis:
I think that the reaction rate for the liver will be faster than the reaction rate of the potato. This is because there is more catalase in the liver. This means that a piece of crushed liver will contain more catalase than a piece of crushed potato of the same mass. From my research I know that the higher concentration of catalase there is then the faster the reaction rate will be. Because liver has a higher concentration of catalase than potato does it means that when it is placed in hydrogen peroxide it will produce more oxygen in a set time limit.
Pilot study:
Before I could do my experiment I had to do a pilot study to find out which measurements I should use to get the best results. First of all I tried to measure the reaction rate of 5g of crushed potato in 20 mls of hydrogen peroxide diluted with 20 mls of water. This gave a measurable result so I decided to continue with these masses and volumes of reactants except this time I tried it with crushed liver instead of potato. The reaction this time however was too volatile so I had to rethink my quantities. I tried the experiment with only 2g of crushed liver and I used a bigger beaker to contain the reaction better. This time the result wasn’t so volatile and the reactants and products stayed inside the beaker. To make sure that this would give a measurable result I repeated the experiment again but using 2g of crushed potato. The reaction was quite slow but measurable so I decided to continue with these amounts for my real investigation. I also found out that the potato reaction starts to stop after three minutes so I decided to record the mass every 20 seconds for three minutes.
Method:
First of all I weighed out 2g of the internal tissue of a potato on and 2g of liver on the top pan scales. Then using the pestle and mortar I separately crushed up the two reactants. To help crush the liver a pinch of sand was placed in the mortar. Then I measured out 20 ml of hydrogen peroxide and diluted it with 20 ml of water making a 50% concentration solution of hydrogen peroxide. Next I placed my 500 ml beaker on the top pan scales and returned the weight to zero. After adding my potato to the beaker I added the hydrogen peroxide and recorded the weight in my table. Every 20 seconds after this I recorded the weight on the top pan scale. I continued to take readings for three minutes aggravating the solution after every reading.
After three minutes was over I repeated the experiment keeping everything the same except this time I used 2g of crushed liver instead of potato. Once this experiment was over I repeated the potato experiment and then I repeated the liver experiment. This was to give a more accurate set of results.
Diagram:
Instead weighing the difference during the reaction I could’ve measured the reaction rate through displacement. This would mean that I set up my experiment as shown below and measured the amount of water that is displaced from the measuring cylinder.
To make this a fair test I used the same concentration of hydrogen peroxide each time I did the experiment. This is because the concentration of the hydrogen peroxide could affect my results. I also made sure that I used the same mass of potato and liver, as I wanted to compare them. If they had different masses it may possibly have affected my results. The experiment was also made a fair test because I used the same top pan scales each time I did the experiment. Using different equipment may have meant I got a different accuracy in my results. I also used the same potato and the same liver for when I repeated my results. I repeated my results so that I could get an average and get more accurate results. If I had used different potatoes and liver there would have been a difference in the amount of catalase and this would’ve changed my results or made then inaccurate.
To make sure that I was making my experiment as safe as possible, I had to do a risk assessment of my experiment. First I checked out how hazardous the hydrogen peroxide was. I found out that it was corrosive, however it was safe to use in 2 mole amounts. This was why the hydrogen peroxide I used had a molarity of 2 moles. I also used gloves, safety goggles and a lab coat to make sure that I was protected.
Results:
During my reaction I noticed that the hydrogen peroxide solution fizzed and gave of a gas. My research indicates that this gas was oxygen because the formula for the reaction between hydrogen peroxide and catalase is:
Hydrogen peroxide + catalase water + oxygen
Analysis:
From my graph I can see that my prediction was correct. I predicted that the liver would have a faster reaction rate than the potato when mixed with the hydrogen peroxide. I can tell that this is true form my graph because the line for the liver reaction rate is steeper that the line for the potato reaction rate. This means that the liver has a faster reaction rate than potato does. This also means that liver contains more catalase that potato does. I know this because my research shows that when there is a higher concentration of catalase then there is a faster reaction rate. When there is a larger concentration of an enzyme the reaction rate of the solution will speed up. This is because there are more enzymes that are able to make successful collision with the particles and cause a reaction. This principle is based on something called the collision theory. This theory states that for two particles to react they must collide with each other and if they collide correctly they react. This is called a successful collision. If there are more enzymes then there will be a larger chance of a successful collision
Evaluation:
Even though I get the results I was hoping for I still got some anomalous results in my graph. This could’ve been for a number of reasons. For instance because I was using very delicate measuring scales a little disturbance in the air could’ve changed my results. Also because after every 20 seconds I was agitating the reactants and placing the beaker on the scales I could’ve placed it in a different place each time and this would’ve changed my results. Or when I was agitating the reactants I could agate it more sometimes and this would’ve caused a faster reaction.
I think that my experiment was very valid. This is because it gave the expected results. If my results had not shown what was expected then, I would’ve redone my experiment to find out where I went wrong.
If I were to do the experiment again I would try to do it in a place with less people. This is because whilst I was doing my experiment there were a lot of people walking around. This caused a draft around my experiment and it changed my results. I would also repeat my experiment more so that I could get a more accurate result.
I would take this experiment further by finding out if other organisms held more catalase. For instance I could see if the potato skin had more catalase in them then potato flesh does. I could also find out if kidneys had a faster reaction rate than liver. I would do the same experiment using the same measurements but I would use a wider variation of reactants.
