Catalase
2H202----------------> 2H20 + 02
Question:
What is the effect of the concentration of hydrogen peroxide on the rate of its reaction with catalase into water and oxygen?
Variables:
Independent variable:
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Concentration of Hydrogen Peroxide (5%, 10%, 15%, 20% solution)
The range of concentrations should be large enough for me to collect enough data to observe correlation between the concentration of hydrogen peroxide and the rate of reaction. Since 20% hydrogen peroxide solution is relatively high, the peak catalysis rate should be observed before it reaches 20%.
Dependent variable:
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Rate of reaction (cm3s-1)
I believe a change in the concentration of hydrogen peroxide will have an effect on the rate of reaction. I will measure the rate of reaction by measuring the volume of the reaction’s product: Oxygen over a period of time.
Controlled Variables:
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Volume of reactants (25 cm3 peroxide to 2 cm3 catalase)
The volume of the reagents will be closely controlled to ensure results reflect the effect of concentration, not a fluctuation of the volume of reagents. The volume of the chemicals will be controlled by carefully measuring it out with a measuring cylinder. However as there measuring cylinders could only measure liquids accurate to the first decimal place there will be an uncertainty of + 0.05.
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Concentration of Catalase (0.5% solution)
The concentration of Catalase will be kept constant by using the same stock of Catalase for all reactions and by refrigerating it between trials to avoid the denaturation of the enzyme by heat.
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Time of reaction for each sample (60s)
The time is very important in the calculation of the rate of reaction because I am calculating it as the volume of gas produced over time. I will control the time of the reaction by using a stopwatch and unplugging the gas syringe when one minute is up to prevent any more gas to be recorded.
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Light intensity
The light intensity under which the reaction is taking place is very important because hydrogen peroxide naturally decomposes under light. I will control this variable by ensuring the light levels are the same when each reaction is taking place.
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Consistency of chemicals
Though the quality of the chemicals could not be completely guaranteed, I can ensure my results are comparable by using the same stock of chemicals and refrigerating it between trials.
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Temperature
For the most accurate results, the entire experiment should take place under thermostatic conditions because temperature is a factor in the rate of reaction. I did my experiment at room temperature which is controlled by a thermostat.
Uncontrolled Variables:
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Quality of chemicals and equipment
As I only have access to shared school equipment and chemicals, its quality and cleanliness could not be completely guaranteed. Though this could be offset by purchasing new equipment for the best results, the costs of such undertaking outweigh the potential improvement of accuracy.
Apparatus:
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50 cm3 Glass syringe (to measure the gas given off)
- Rubber tubing connected stopper (to connect conical flask to syringe)
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50 cm3 Conical flask
- Boss and clamp stand
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25 cm3 Measuring cylinder
- Stop watch
- Safety Equipment
- Safety goggles
- lab coat
- gloves
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10cm3 0.5% Catalase solution
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25 cm3 of 5%, 10%, 15%, 20% Hydrogen Peroxide solution
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25 cm3 of distilled water for control experiment
Method:
- Set up equipment with syringe held horizontally by the clamp and rubber tubing connecting syringe to the stopper. Check for leaks by blowing into system and watching for escaping air.
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First prepare the control experiment by measuring 25 cm3 of distilled water with measuring cylinder and pour into conical flask.
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Add 2 cm3 of 0.5% catalase to the distilled water in the flask and immediately seal flask with stopper, and start timer. With this closed system, all gases produced by the reaction in the flask should exit the flask through the rubber tubing and enter the syringe.
- When 1 minute is reached, disconnect the stopper from the conical flask.
- Record how much gas had been produced at eye level.
Repeat process and replace distilled water with 5%,10% and 15% concentrations of hydrogen peroxide.
Note: Time between step 3 and 4 must be kept minimal because hydrogen peroxide breaks down under light. Check for leaks at all times and make sure the plunger is not stuck.
Results:
5% H202
10% H202
15% H202
0% H202 (Control Experiment using distilled water)
Calculations:
Mean:
5% H202
(0.48 + 0.58 + 0.53 + 0.43)/4 = 0.505
10% H202
(0.84+0.8+0.78+0.93)/4 = 0.8375
15% H202
(1.28+1.3+1.23+1.33)/4 = 1.285
Standard Deviation:
5% H202
(0.48 + 0.58 + 0.53 + 0.43)/4 = 0.505
(0.48-0.505)2 =0.000625
(0.58-0.505)2 =0.005625
(0.53-0.505)2 =0.000625
(0.43-0.505)2 =0.005625
0.000625+0.005625+0.000625+0.005625= 0.0125
= 0.180
10% H202
(0.84+0.8+0.78+0.93)/4 = 0.8375
(0.84-0.8375)2 =0.00000625
(0.8-0.8375)2 =0.00140625
(0.78-0.8375)2 =0.00330625
(0.93-0.8375)2 =0.00855625
0.00000625+0.00140625+0.00330625+0.00855625=0.013275
=0.058
15% H202
(1.28+1.3+1.23+1.33)/4 = 1.285
(1.28- 1.285)2 =0.000025
(1.3- 1.285)2 =0.00000225
(01.23- 1.285)2 =0.003025
(1.33- 1.285)2 =0.002025
0.002025+0.00000225+0.000025=0.00205225
= 0.023
Conclusion:
The results being, 0.51, 0.84 and 1.29 positively correlate with the concentration of Peroxide therefore supporting my hypothesis which is that the higher the concentration the larger the volume of gas produced. The results are fairly accurate because all the points fell on the line of best fit with the small discrepancy of the 10% hydrogen which was probably due to the fact that those set of results were taken on a different day than the rest of the results. The small error bars also the small variance of the results show the accuracy of the results.
Evaluation:
There were a number of factors that affected the accuracy and outcome of the experiment. Firstly, environmental factors to the experiment such as temperature and light affect the results of the experiment greatly so should be reduced to the lowest level possible or kept constant. The volume of light is also critical to the precision of the experiment as we are using hydrogen peroxide which is an unstable compound that breaks down in light. As we did this experiment over a couple of days, the temperature of the room and chemicals were not the same for each day which caused anomlies in our results because temperature affects the rate of reaction. Secondly, problems with and difference in the equipment and chemicals used cause discrepencies in our results so should be checked carefully. Our apparatus included a gas syringe which meant that there could be a lot of problems to be expected and was right, the plunger of the syringe often got stuck and on the different days we might get different syringes meaning our results were not very accurate and consistent. Lastly, human error must be considered as the experiment was carried out by humans and mistakes are inevitable.
Many of these factors could be eliminated or minimized if the following precautions are taken. The environmental factors could be eliminated in the future by immersing the chemicals in a water bath at a fixed temperature to make sure the reagents are at the same temperature when reacting, as well as by carrying out the experiment at the same time of day each day so that the room is aproximately the same temperature. To minimize light exposure during the experiment the lights should be turned down when doing the experiment and to promptly carry out the experiment, not letting it break down in the light. This could be eliminated by using high grade equipement and using the same equipment each time to ensure reliable and comparable results. This experiment requires a lot of accurate measuring for the experiment to be reliable however human error may compromise this. This can be reduced by having more skilled people to help in the experiment and everyone having their own job as well as taking care when taking measurements.
