2H202 2H20(l) + 02 (g)
However, hydrogen peroxide is toxic and does not break down quickly enough and to prevent damage to the cell. Therefore all living cells contain the enzyme catalase, which speeds up the decomposition of hydrogen peroxide. Enzymes are biological catalysts. A catalyst speeds up a reaction by remains chemically unchanged. Enzymes are used to make reactions happen quickly to keep us alive. There are two types of enzymes the breakers and builders. Builders join molecules and breakers break down larger molecules to smaller ones. For instance, H202 into smaller ones e.g. H20 and 02. Therefore we know that catalase is a breaker enzyme as it is breaking the hydrogen peroxide into water and oxygen. All enzymes are proteins and control particular reactions and can be used again and again. They are affected by temperature and pH. In my experiment I am using a potato as my source of catalase. The temperature of the reaction will be kept constant at room temperature 27 degrees centigrade. The pH will also be kept constant as the H202 is neutral, there the products should not change pH and should also remain neutral.
Catalase is stored in compartments within a cell called peroxisomes, which is inside the cell wall and the cell membrane. When the cell is cut or broken the catalase is released. The catalase can then act on the hydrogen peroxide and break it down. The catalase aids the breaking and making of bonds between the H202 molecules and makes H20 and 02.
When a cube of potato is chopped into smaller pieces it’s surface area increases and therefore by breaking more of the potato cells we release more catalase, which will speed up the reaction of decomposing the hydrogen peroxide more quickly. The more catalase that is exposed the more hydrogen peroxide will be decomposed. The increased quantity of the catalase increase the chance of the molecules colliding with each other, as there are so many of them. Enzymes and substrates need to meet in a particular way, this is called a lock and key reaction. The molecules constantly move and bump into each other. When the substrate molecule bumps into a molecule of the right enzyme, it fits into a depression on the surface of the enzyme called the active site. The reaction takes place and the molecules of the product leave the active site freeing it for another substrate to fit into. The active sites are specific shapes so only a certain type of substrate will fit into it. They fit as if they were a lock and key (hence the name).
The more molecules there are, the more chance that the enzyme catalase the sub-straight hydrogen peroxide will meet with each other and react, allowing the enzyme to catalyse and increase the rate of reaction.
The more the reaction occurs the more oxygen gas and water will be produced. This leads me to a prediction that if the surface area is doubled the chance of collision is also doubled and therefore the rate of reaction and gas produced should also double. This should also be true if you were to triple or quadruple the surface area.
Therefore I am going to use the oxygen gas collected to show how the rate of reaction is changed.
Therefore I predict that when I increase the surface area of potato exposing more catalase it will increase the rate of reaction and therefore increase the amount of oxygen gas produced. When I double and triple the surface area I should see a double and triple in the volume of gas produced. I predict that the surface area exposed will be directly proportional to the oxygen gas produced and therefore my graph will have a straight line through the origin.
An experiment to investigate the effect of changing the
Surface area of a potato chip on the reaction
Between catalase and hydrogen peroxide
Apparatus
Safety goggles
Test tube rack
Scalpel
Ruler
Stop clock
Cutting tile
Method
The apparatus will be set up as shown. A potato chip of surface area 6cm2 will be put into a test tube of H2O2 (as shown in the diagram above) and will be timed for five minutes. During this time the volume of gas produced by the reaction will be collected in a measuring cylinder. The experiment will be done 7 times with a chip the same size but the surface area will be changed; this will give seven readings. The surface area will be increased by 2cm2.This will be done by cutting a slice off and therefore exposing two extra surfaces of the 6cm2 cube(as each face is 1cm2). The whole of the chip will be put into the test tube so that the mass remains constant. The surface area of each chip will be measured to the nearest 0.1cm2 using a ruler and the volume of oxygen gas collected will be measured to the nearest 1cm using the scale on the measuring cylinder.
The surface area will range from 6-18cm2 which gives us a total of seven readings.
The surface area is the variable that I chose to change and the mass is kept constant as initially all the chips a re the same size.
The experiment will be repeated to establish a similar pattern of readings, all the potato cubes will be measured accurately with a ruler, which makes the experiment accurate.
To make the experiment safe I will wear safety goggles so that the corrosive hydrogen peroxide doesn’t go in my eyes and I will also take great care when cutting the potato so that I do not cut myself.
The Preliminary Experiment
I did a preliminary experiment to check that my theory was correct and so I could accurately set up my experiment.
I set up my experiment as shown in the method but only collected the gas of the largest surface area and the smallest surface area. Which were 6cm and 18cm .
Surface Area (in cm2) Oxygen gas collected (in cm3)
to the nearest 1cm3
To the nearest 0.1cm
G1 G2 Average
6.0 6 5 6
18.0 19 18 19
The surface area of the potato chip affected the amount of gas collected and therefore the rate of the reaction. Therefore my prediction was right.
I did the experiment and it worked well so I decided to go ahead and use this experiment and the surface area of the chip as my final factor.
When the gas was collected for the smallest area chip it seemed there was not a lot of gas displaced in the measuring cylinder. This was because the cylinder I had used had a very large scale on it. This indicates that I may have to use a smaller measuring cylinder to collect the gas of the chips with a smaller surface area and then change to a larger one for the chips with a larger area. So that the readings can be more accurate.
Another samll problem was when I set up my experiment I already had the delivery tube in the water, which meant I got suck back which I notice and decided to set up the experiment and then put the delivery tube in the water so as not to get suck back, which would bring my results down lower, as water would have to be pushed out of the tube.
