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The Decomposition of H2O2 using Catalase, in yeast as a catalyst.

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The Decomposition of H2O2 using Catalase, in yeast as a catalyst. Prediction Hydrogen Peroxide decomposes to water and oxygen. When yeast is added, the enzyme Catalase in the yeast speeds up the decomposition. The formula for the decomposition of H2O2 with Catalase is: Catalase H2O2 H2O + 1/2 O2 Reactions in living cells, for example, liver cells, produce H2O2, which is poisonous. Catalase renders it harmless by breaking it down into oxygen and water. This is a catabolic reaction, meaning that the H202 molecule is split into two smaller molecules, H20 and 1/2 O2. This can be explained using the lock and key theory. All enzymes are specific, which means we can think of Catalase as a lock, which is shaped so that H2O2 is the only key that will fit and the only molecule it will break down. The Catalase speeds up the decomposition of H2O2 because it is a catalyst; this means it can take part in a reaction without undergoing a permanent change. A Catalase molecule can break down H2O2 into 1/2 O2 and H2O many, many times without undergoing a permanent change. Catalase speeds up the reaction because it lowers the activation energy required for the H2O2 to decompose. It provides an alternative route of lower activation energy. The energy needed to start the decomposition is lower because the Catalase weakens the chemical bonds by forming weak interactions with the H2O2 molecules. I am going to investigate the effect of temperature on the rate of decomposition of H2O2. I predict that as the temperature increases, the rate of reaction will increase. Mackeans says, "An increase of temperature of 10?C will double the rate of reaction." So I predict that if at 20?C I saw 15cm3 of oxygen given off in 15 seconds, then at 30?C I would see 30cm3 given off in the same time period. The rate of decomposition increases because the kinetic energy of the Catalase and H2O2 molecules increases as the temperature rises. ...read more.


For these higher temperatures the water will need to be heated with a Bunsen on the blue flame. For 60?C and 70?C I will carry out the experiment with the water bath and boiling tube still being heated by the Bunsen on a low flame because this is a high temperature and this will be more accurate as the temperature will not drop which would affect the results. The experiment needs to be carried out at all the temperatures three times. Safety 100 vols. of H2O2 is corrosive 20 vols. of H2O2 is an irritant - dangerous if swallowed Less than 18 vols. H2O2 to produce minimal hazard - I am using 5 vols. of H2O2 which is well with in the minimal hazard range. I will be wearing goggles and should any spillage on myself or on other surfaces occur, I would wash it off with lots of water immediately. Because H2O2 is flammable, I shall take special care around the Bunsen burner as oxygen-rich air promotes burning. Obtaining This table of results shows the raw data from the experiment. Time (Minutes and seconds) Volume of O2 given off at 20?C (cm3) Volume of O2 given off at 30?C (cm3) Volume of O2 given off at 40?C (cm3) Volume of O2 given off at 60?C (cm3) Volume of O2 given off at 70?C (cm3) (Repeats) 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 0.15 6 4 7 7.5 11.5 8 10 14 10 3.5 6 4 4.5 2.5 2 0.30 14 5 13 14 19 15 17 29 21 6 9 7.5 7 4 4 0.45 17 6 18 20 28 21 20 34 28 10 13 10 8 5 4 1.00 20 14 23 24 28 29 21 36 32 11.5 16 14.5 9 6.5 5.5 1.15 24 20 25 28 31 34 22 36 34 14.5 18.5 16 10 8 6 1.30 26 25 28 32 33 34 23 36 35 17 22 18 ...read more.


It is however impossible to say if the temperature remained constant through out all the tests at one temperature, especially the higher temperatures of 60 and 70?C even though a water bath and Bunsen burner were used. This could make a big difference to the results, because if the temperature was supposed to be 30?C but it had dropped to for example 24?C it would be difficult to tell because water is a poor conductor and the thermometer might not measure the temperature drop. So this theoretical set of results could be closer to what they should be at 20?C and bring the average down. In an ideal situation, the best thing to use in this experiment would be an electrical thermostatically controlled water bath, then the results would almost certainly be more accurate because the temperature would be kept more constant. Finally, another reason that the results for the higher temperatures of 60 and 70?C could be inaccurate is the fact that gas expands at high temperatures, so the oxygen could have taken up a larger volume than there was oxygen actually produced. If I was to carry out this experiment again I would definitely try the experiment at 50?C because it is unclear from my results what happens after the optimum of 40?C has been reached. I would also probably experiment with smaller intervals of temperature, maybe using 5? intervals, which would again give me a better idea of the curve on the rate of reaction against temperature graph, because I wasn't actually able to draw a smooth curve. If I was going extend the experiment, I would maybe repeat the same experiment but with small pieces of liver instead of yeast, as it also contains catalase and it would be interesting to see if the results from the two experiments were similar. I might also use a narrower temperature range between 30, 40 and 50?C to find out exactly where then optimum temperature was. Chemistry/Biology joint investigation - 1 - ...read more.

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