Research Question How does the concentration of catalase affect the speed of the decomposition reaction of Hydrogen Peroxide into oxygen and water?

Transcription

1 Research Question How does the concentration of catalase affect the speed of the decomposition reaction of Hydrogen Peroxide into oxygen and water? Aim To observe the effect of increasing enzyme (catalase) concentration on the speed of decomposition of Hydrogen Peroxide, by measuring the change in concentration of oxygen inside the reaction flask. Hypothesis Increasing the concentration of enzyme should increase the speed of the reaction. Variables Independent Variable Concentration of Enzyme Dependent Variable Gradient of Concentration of Oxygen/Time graph Controlled Variables Total initial volume of gas in reaction flask Initial oxygen concentration in the gas in the reaction flask Temperature External kinetic factors-vibration sources etc. ph value of the solutions Concentration of Hydrogen Peroxide solution. Apparatus Computer Lab Quest Device Oxygen Probe Flask(500 ml) 6 Beakers(500 ml) Small Beaker(50ml) Graduated dropper Stirrer Electronic Balance Graduated Cylinder(100 ml) Dish Funnel Spatula Paper Towels Thermometer Glass rod A pair of gloves Chemicals Water Yeast powder Hydrogen peroxide(10%)

2 Method Firstly five solutions with different concentrations of enzyme were to be prepared. Since the enzyme catalase is found in yeast cells, yeast powder was used as the source of the enzyme. It was assumed that the mass of yeast powder would be directly rational to the mass of the enzyme it contained. Thus changing the mass of yeast powder added to each solution would mean a proportional change in the enzyme concentration of the solutions. As a precaution, a control group, containing no yeast added, was prepared and labelled as solution 6. The masses of yeast powder were to be in a logarithmic sequence, so that an easily observable change would occur due to changing concentration. 0.25mg of yeast powder was to be added to Solution 1, 0.50 to Solution 2, 1.00 to Solution 3, 2.00 to Solution 4 and 4.00 to Solution 5. No yeast was added to Solution 6, for that it would be the control group for the experiment. Table 1 To prepare solutions of different concentrations of catalase enzyme, 100ml of water was poured into each 6 beakers and beakers were labelled. Desired masses of yeast powder were placed onto a dish on electronic balance with the help of a spatula. Each time a different mass of yeast powder was placed onto the dish. Each time the dish was wiped with a dry paper towel to ensure no unwanted particles remained on it. When the dish was placed on the electronic balance its tare was determined to ensure a good and accurate reading. Each different mass of yeast powder was poured into a labelled beaker containing 100 ml water, on which was written the mass of yeast to be added, by using a funnel. The funnel was wiped with dry paper towels after each time. Once the yeast powder was poured into a beaker the mixture was stirred using a glass rod to ensure all the powder dissolved in water. The prepared solutions were shaken frequently to prevent yeast precipitating at the bottom of the beakers.

3 After the solutions were ready, a small beaker was filled with 10%Hydrogen Peroxide solution till a half of it was full to be used for the experiment. During this process and for the rest of the experiment, gloves were worn to avoid exposure to toxic hydrogen peroxide. To create a reaction chamber and observe the speed of reaction, The Lab Quest device was turned on and connected to the computer. The oxygen probe was connected to the Lab Quest device and identified by the computer. The oxygen probe was tested if it fitted to the flask in which the reaction was to take place. The flask was washed cleanly and placed upside down to avoid water droplets remaining inside it. For the reaction and data collection, Required solution was poured into the flask in which the reaction was to take place. The graduated dropper was filled up to 2ml level with hydrogen peroxide from the small beaker. The hydrogen peroxide was dropped into the graduated cylinder till 1ml level, so that only 1ml of it was poured into the flask. Immediately, the oxygen probe was placed on top of the flask and fitted there tightly and it was set to start taking readings of oxygen concentration each second. For 240 seconds readings were taken in terms of % concentration of oxygen in the flask and graphed in the mean time. At the end of the 240 seconds, the probe was set not to take any more readings. Flask was emptied and washed cleanly. The process was repeated for all the solutions, including number 6, the control group. For keeping the controlled variables constant throughout the experiment, Throughout the experiment neither the volume of yeast solution poured into the flask (100 ml) nor the volume of the Hydrogen Peroxide solution were changed. Thus the volume of liquids inside the flask was constant which in turn means that the total initial volume of the gas inside the flask was kept constant. The experiment was carried out in a well-ventilated laboratory which must have the same oxygen concentration in the air inside it. A fast fluctuation in the oxygen concentration during the time at which the whole experiment was carried out was not possible. Thus the initial oxygen concentration of the gas inside the flask was kept constant. All of the liquids used in the experiment waited in the laboratory for over 20 minutes. This means that the temperature of the liquids should have been nearly equal to the temperature of the lab. In that way at least the initial temperature was kept constant for

4 all solutions. The experiment was carried out on a bench that was firmly fitted to the floor. Also the flask was not shaken throughout the experiment for none of the solutions. Thus the external kinetic factors were kept constant. All of the apparatus used in the experiment -beakers, measuring cylinder, flask, dishwere cleanly washed before use to avoid any contaminants that would effect the ph value of the solutions. Also all solutions were prepared using the same source of water, hydrogen peroxide solution and yeast powder, which equalises the factors effecting ph for all solutions. Thus the ph values of the solutions were kept equal in an indirect way. The hydrogen peroxide solution was the same for all the solutions prepared. Thus the concentration of hydrogen peroxide was kept constant as it was being the same for all of the solutions. Results Described The results of the experiment were graphed automatically and saved. Since it is not possible to display the graph here, it will be verbally and comparatively described. The result for solution 1 was a smooth line with a slightly small gradient. The result for solution 2 was a relatively steeper graph with a greater gradient compared to that of solution 1. The result for solution 3 was a steeper graph than that of solution 2. The results for solutions 4 and 5 were strangely similar graphs which barely showed any signs of increase in the concentration of oxygen in the flask which seems to be against the hypothesis. The result for solution 6 was, as expected, a linear graph with no indication of increase in oxygen concentration. Conclusion and Evaluation In general the experiment was carried out carefully. The presumed values for the amounts of water and yeast powder for solutions were adjusted to give the lowest inaccuracy in the experiment. Despite the rigorous effort of one to keep every aspect of the experiment near to precise, some of the results were surprisingly strange. The results for solutions 1, 2, 3 and 6 are showing an expected rational relation between the concentration of enzyme and the speed of reaction, whereas the results for solutions 4 and 5 are out of ordinary. They show just the opposite of what was expected. This vague shift between the results solutions 1,2,3,6 and 4, 5 can be explained by the visual observations made during the experiment. For solutions 1, 2, 3 and 6, nearly no bubbles had formed. Even though as the concentration of yeast powder increased the amount of bubbles increased, the bubbles didn't make up a grand problem till solutions 4 and 5 which contained

5 twice and four times the amount of yeast powder respectively. Most probably the bubble formation prevented the oxygen from mixing into the gases in the flask, which is essential for the observation to be made. Simply because the oxygen probe was only able to measure the oxygen concentration in the gas that reached it, it was unable to measure all of the oxygen produced in solutions 4 and 5 where the oxygen was trapped in bubbles and never mixed into the gas which the probe measured. To prevent the bubble formation, all the solutions could have been mixed in the same pattern that the forming bubbles would pop up and release the oxygen. Even better, a different means of measuring the gas produced could be used. A good suggestion would be to measure the change in gas pressure using a pressure probe. In addition to the bubble formation, gases escaping from the flask to outside through the gaps between the probe and the flask form another source of error in the experiment. This could have been avoided by using some plastic sheeting to cover up the gaps and some thread to tighten the plastic cover. Keeping the temperature constant through the experiment is another weak point of the experiment. Given that the decomposition reaction of hydrogen peroxide is an exothermic reaction, heating up is a major problem for the accuracy of the experiment. To avoid this a water bath could be used to keep the flaks and its content at the same desired temperature of 25 Celsius degrees.