The enzyme works as a catalyst. This works by giving the reacting particles a surface area to stick to, where they can bump into each other. This increases the number of successful collisions, and therefore the speed of the chemical reaction is increased.
Molecules are constantly moving around and bumping into each other. When a substrate molecule, in this case hydrogen peroxide, bumps into a molecule of the right enzyme it fits into a depression called the active site on the surface of the enzyme molecule. The reaction then takes place and the molecules leave the enzyme, freeing it for another substrate molecule.
The active site of a particular enzyme has a specific shape into which only one kind of substrate will fit. The substrate fits into the active site in a similar way as a key fits into a lock. This is why enzymes are specific in their action.
Enzymes lower the amount of activation energy required for a chemical reaction to take place. To do this the substrate molecule must fit perfectly into the enzyme at the active site. Because the substrate must fit into the active site, the action is similar to a lock and key.
The substrate is the hydrogen peroxide and the products of the reaction are water and oxygen.
In order for my findings to be accurate, my test must be both fair and reliable. To make sure of this I will:
- Make sure the same person always takes the timings with the stop watch
- Use clean equipment for each experiment to avoid cross contamination
- Use the smallest measuring cylinders available for measuring chemicals for accuracy
- Always use the same amount of the enzyme for each experiment
- I will repeat the experiment for each temperature 3 times and take averages to improve the credibility of my findings
These precautions will make my final results more reliable and keep anomalies at a minimum, making the investigation more successful.
Safety precautions
I will be very careful whilst handling the hydrogen peroxide as it burns skin. I will wear goggles to protect my eyes and immediately mop up any spillages. I will stand up whilst carrying out the experiments so that I have more control over what I am doing.
Preliminary experiment
The chemical reaction I will investigate uses hydrogen peroxide and an enzyme. When the two solutions are mixed together, gas is given off as the reaction takes place.
Equation
Hydrogen Peroxide → Water + Oxygen
2H20 → 2H20 + 02
Firstly I am going to carry out an initial experiment with 10cm3 hydrogen peroxide at 100% concentration and 5cm3 catalyse enzyme.
Equipment
- Washing up bowl half full of water
- Large measuring cylinder
- Two small measuring cylinders
- A conical flask with a bung
- Delivery tube
- Stop watch
- Goggles
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10cm3 hydrogen peroxide
-
5cm3 enzyme
Diagram
Method
- Fill the large measuring cylinder with water and invert it into the washing up bowl
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Measure out 10cm3 hydrogen peroxide and pour into the conical flask
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Using a clean measuring cylinder, measure out 5cm3 enzyme
- Place the delivery tube so that one end of it goes up into the large measuring cylinder
- Pour the enzyme into the conical flask with the hydrogen peroxide and immediately place on the bung and start the stop watch
- Time for one minute and take a reading of the amount of gas in the large measuring cylinder
Results
Average 94.3 cm3 of gas
I am now going to repeat the experiment although this time I will change the concentration of the hydrogen peroxide. I expect that the stronger the hydrogen peroxide is, the more gas will be collected in the large measuring cylinder. This is because as the concentration of substrate is increased, there are more hydrogen peroxide molecules available to fill the active sites and react. This raises the rate of product formation and therefore the rate of the reaction.
For this experiment I will use exactly the same equipment as in my previous plan, but will also need water to weaken the strength of hydrogen peroxide.
Method
- Fill the large measuring cylinder with water and invert it into the washing up bowl
- Measure out the given amount of hydrogen peroxide and pour into the conical flask
- If required, measure out the given amount of water using a clean measuring cylinder and pour this into the conical flask with the hydrogen peroxide
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Using a clean measuring cylinder, measure out 5cm3 enzyme
- Place the delivery tube so that one end of it goes up into the large measuring cylinder
- Pour the enzyme into the conical flask with the hydrogen peroxide and immediately place on the bung and start the stop watch
- Time for one minute and take a reading of the amount of gas in the large measuring cylinder
Results
* This result was an anomaly so I repeated this and got 52. This result fits in with the rest of my results and brings the average for 60% strength to 55.
Analysis of results
My results show a trend of the stronger the concentration of hydrogen peroxide, the quicker the reaction takes place and therefore the more gas is collected. The graph shows this with a smooth curve of positive correlation where when the concentration of hydrogen peroxide is increased, the average volume of gas collected also increases. This is because as the concentration of substrate (hydrogen peroxide) was increased, there were more hydrogen peroxide molecules available to fill the active sites and react. This caused the rate of product formation and therefore the rate of the reaction to increase, showing a smooth curve of positive correlation on my graph.
My results perfectly match my prediction as after repeating one experiment to eliminate an anomaly there are no odd results. The line of best fit on my graph goes perfectly through all the plotted points and is a smooth curve showing that as the concentration of hydrogen peroxide is increased, the average volume of gas collected increases.
Evaluation of results
My method gave me results that matched my prediction. I predicted that the stronger the concentration of the substrate, the faster the speed of the reaction will be. My graph of results matched this prediction accurately as the line of best fit is a smooth positive curve showing a definite correlation between the concentration of hydrogen peroxide and the volume of gas collected.
I got one anomalous result which could have been caused by cross contamination in the measuring cylinders or inaccurate timing of the experiment. I quickly spotted the anomaly and repeated the experiment to gain accuracy in my average set of results.
The only part of the method that I feel could be improved would be to repeat each experiment 4 times rather than 3 because this would make it easier to spot anomalous results and it would make the experiment more accurate and the results more reliable.
It is important to check that results are reliable because they make the experiment accurate. I feel that my results are reliable as took many precautions to ensure the reliability and fair tests of my experiments and there are no results that do not fit in with the line of best fit on my graph.
I have collected sufficient results to make a firm conclusion that the stronger the concentration of the substrate, the quicker the reaction will take place when catalysed by an enzyme.
Another way to investigate the effect of concentration on the rate of a reaction that is catalysed by an enzyme:
- Set up apparatus as in the following diagram
- Record the weight of the empty conical flask
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Pour 5cm3 catalyse enzyme into the conical flask and record the weight of it minus the weight of the conical flask
- Weigh the hydrogen peroxide and record the weight of it separately
- Work out the sum of the hydrogen peroxide and catalyse to get the total weight of them added together in one conical flask
- Pour the enzyme into the conical flask containing hydrogen peroxide whilst it is on the scales and start the stopwatch immediately
- Time 1 minute and record the weight
- Minus this from the total weight to calculate the weight of gas that has escaped during the reaction
- Repeat the experiment with hydrogen peroxide at different concentrations
A problem with this experiment is that very accurate weighing scales are needed to gain a reliable set of results.