The red high-lighted area on the far left is the new energy of activation needed in order to begin the reaction with the hydrogen peroxide and potato. Thanks to this, all the particles after the required energy of a particle has been met can react if they collide.
The green high-lighted area shows the old energy of particles needed for activation.
The enzyme does all of this through a few steps, you can see this on the following diagram, on the next page.
The above diagram shows how an enzyme such as catalase comes in to contact with a substrate and the chemical reaction occurs.
Step 1: The enzyme and substrate are separate at this point.
Step 2: Now, the enzyme, catalase interacts with the hydrogen peroxide (the substrate) in order to create an enzyme-substrate complex as they are both complimentary towards each other.
Step 3: Once, both the enzyme and substrate are joined together to make an enzyme-substrate complex, the active sight (high-lighted grey) alters shape somewhat, and places stress upon the molecular bonds of the substrate in a process named induced fit, this is the process in which the hydrogen peroxide (the substrate) undergoes a chemical reaction and turns in to the products of water and oxygen. This stress reduces the activation energy needed.
Step 4: Finally, the products of water and oxygen are made and the recently occupied enzyme is now ready to repeat these steps. Also, only one enzyme is able to undergo one reaction at a time.
This effect is responsible for the demonstrated change in the dependent variable, the speed of the reaction.
Variables
- Independent Variable
- The independent varaiable throughout our experiment will be the concentration of hydrogen peroxide (H2O2) when using twenty mililitres of the solution. We chose this as controlling the concentration of the hydrogen peroxide is simple and easy to control, this will provide good data for plotting on a graph.
- Dependent Variable
-The dependent variable throughout our experiment will be the volume of oxygen (cm3) produced in 20 seconds. By timing for 20 seconds we found that roughly all of the gas burette (found on: ‘Equipment List’) was full of gas which allowed us to make use of the full range of this piece of equipment.
Equipment List
Below you will see all the equipment used in the experiment along with a diagram and an explanation of why we will use them.
ANALYSIS
Results Table
My results convey a positive correlation between the concentration of hydrogen peroxide and the rate of its decomposition into liquid water and oxygen. All the points on my graph follow a similar pattern: as the concentration of hydrogen peroxide increases, the mean volume of oxygen produced within one minute also increases.
Taking two points on my graph, you can clearly see that when the concentration of hydrogen peroxide is 25% the mean volume of oxygen produced in one minute is 23.58cm3. However, when the concentration of hydrogen peroxide is 50% the mean volume of oxygen produced within one minute is 48.48cm3. These two points show that when the concentration of hydrogen peroxide is doubled, the rate of reaction increases by approximately two, in fact it increases by 2.1 (rounded to one decimal place). When you double the concentration again, from 50% to 100%, the rate of reaction increases 1.7 (rounded to one decimal place), this proves that when the concentration of hydrogen peroxide increase, so does the rate of reaction however, at higher concentrations the effect upon the rate of reaction becomes less.
With the use of a line of best fit we are easily able to predict the mean rate of reactions for various concentrations of hydrogen peroxide which we may not have specifically tested. The following table shows various example concentrations from my line of best fit together with their predicted mean rate of reaction, and the ration between concentration of hydrogen peroxide and the mean rate of reaction.
As you can see, my line of best fit demonstrates the ratio between the concentration of hydrogen peroxide as a percentage and its rate of decomposition in cm3/min to be roughly 1:1.06. This provides a positive correlation on my graph. Three out of the four points on my graph do not run through the line of best fit, however I do not feel as though there is a large enough gap to be considered anomalous. Overall, the points on my graph all increase therefore, this gives me confidence in my method.
Our results plot a straight line of best fit, where there is a fixed ratio between the independent and the dependent variable. However, I believe that, should we have continued to increase the concentration of the H2O2, the line of best fit would have started to flatten, shown in section 2 of my sketch, and eventually flattened (section 3). This is because of the nature of enzymes: the speed at which they can react is limited by the number of catalase particles in the reaction chamber. When a certain concentration of H2O2 is reached, the active sites will become saturated, all of them reacting at their maximum speed, and we would be unable to increase the speed of the reaction further. In order to do this, we would have to increase the amount of potato, and therefore the number of particles of catalase, present in the reaction vessel.
The above diagram shows how an enzyme such as catalase comes in to contact with a substrate and the chemical reaction occurs.
Step 1: The enzyme and substrate are separate at this point.
Step 2: Now, the enzyme, catalase interacts with the hydrogen peroxide (the substrate) in order to create an enzyme-substrate complex as they are both complimentary towards each other.
Step 3: Once, both the enzyme and substrate are joined together to make an enzyme-substrate complex, the active sight (high-lighted grey) alters shape somewhat, and places stress upon the molecular bonds of the substrate in a process named induced fit, this is the process in which the hydrogen peroxide (the substrate) undergoes a chemical reaction and turns in to the products of water and oxygen. This stress reduces the activation energy needed.
Step 4: Finally, the products of water and oxygen are made and the recently occupied enzyme is now ready to repeat these steps. Also, only one enzyme is able to undergo one reaction at a time.
This effect is responsible for the demonstrated change in the dependent variable, the speed of the reaction.
