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Does the Concentration of Hydrogen Peroxide Speed up the rate at which it is broken down by catalase

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Introduction

DOES THE CONCENTRATION OF HYDROGEN PEROXIDE SPEED UP THE RATE AT WHICH IT IS BROKEN DOWN BY CATALASE. AIM To find out whether the concentration of Hydrogen Peroxide affects the rate of decomposition of hydrogen peroxide when broken down by catalase. SCIENTIFIC KNOWLEDGE Hydrogen peroxide is a liquid bi-product of many chemical reactions in living things. It is toxic, so has to be broken down by the enzyme catalase which is also found in most living things. E.g. Hydrogen peroxide catalase water + oxygen 2H2O2 (aq) 2H2 O + O2 The enzyme catalase (peroxidase) was the first enzyme discovered and is one of the fastest enzymes, its turnover rate is about 40,000 molecules/second. It speeds up the decomposition of hydrogen peroxide. * Enzymes are not used up by the reaction and remain unchanged. * Enzymes work most efficiently at their optimum temperature and optimum pH, which from a previous experiment, I know to be about pH8 * Can be denatured (changed in shape) by excess heat (+45�C) and/or extremes of pH. * Very specific to their substrate molecule. THEORY COLLISION THEORY Enzymes are biological catalysts. They tend to speed up the rate of biochemical reactions. Decomposition of hydrogen peroxide 2H2O2 (aq) 2H2 O + O2 The enzyme catalase (peroxidase), catalase was first enzyme discovered. It is one of the fastest enzymes, with a turnover rate of about 40,000 molecules/second. Speeds up the rate of decomposition of hydrogen peroxide active site catalase hydrogen peroxide catalase hydrogen peroxide water oxygen enzyme-substrate complex enzyme unchanged products Enzymes are not used up and are unchanged by the reaction. Enzymes work most efficiently at an optimum temperature and an optimum pH. Rate of reaction a. without enzyme Volume of b. with enzyme oxygen/min Time in minutes NB rate of reaction is the actual number of substrate molecules evolved per minute. Volume of oxygen produced/evolved per minute is not in itself the rate of reaction, but is indicative of the actual rate of reaction. ...read more.

Middle

The result highlighted in pink, I have labelled a1 (anomaly1). This is because it is nowhere near the others, the total volume of oxygen produced shouldn't even have doubled from 20vol, instead it has more than trebled. The only thing I can blame this on is that maybe the other concentrations were far older, therefore had partially decomposed already. This is also the same with the first set of results; there should have been a 25% increase in volume of oxygen produced between 20vol and 25vol, instead it approximately doubled. This supports the theory that the 25vol may have been made up far more recently. Hydrogen peroxide decomposes to hydrogen and water naturally over time. So if the other concentrations had been made up a while ago, then this would have already started to happen, meaning there would be fewer molecules of hydrogen peroxide for the catalase to decompose. This may also explain why there is no increase in total volume of oxygen between 5vol and 10vol in the second experiment, although in the first experiment, excluding the result for 25vol there is a reasonable pattern of doubling. In the second experiment 2.5vol to 5vol more than trebles, 5vol to 10vol doesn't increase and 10vol to 20 is the only one that nearly doubles. I have also done two graphs comparing the rates of reaction for each concentration in each experiment. This is so I could look at the rates of reaction and see the way the rates of different concentrations change each minute. With 25vol in the first minute the rate of reaction is significantly higher than in the second and third minutes, this is not true with the other concentrations, where the rate of reaction decreases by about the same amount each minute. Also as the concentration decreases, the gradient of the line also does, this tells us that there is less difference in the rate of reaction between the first second and third minutes. ...read more.

Conclusion

Rate of reaction 25 0.5 15 15 25 1 22 7 25 1.5 28 6 25 2 33 5 25 2.5 38 5 25 3 42 4 20 0.5 7 7 20 1 14 7 20 1.5 19 5 20 2 23 4 20 2.5 28 5 20 3 32 4 10 0.5 5 5 10 1 11 6 10 1.5 15 4 10 2 19 4 10 2.5 23 4 10 3 25 2 5 0.5 3 3 5 1 5 2 5 1.5 7 2 5 2 8 1 5 2.5 11 3 5 3 13 2 2.5 0.5 1 1 2.5 1 1 0 2.5 1.5 1 0 2.5 2 1 0 2.5 2.5 1 0 2.5 3 2 1 Results of Follow-up Experiment (2) H2 O2 concentration (vol) Time (minutes) Oxygen foam produced (ml) Rate of reaction 25 0.5 12 12 25 1 19 7 25 1.5 22 3 25 2 32 10 25 2.5 38 6 25 3 43 5 20 0.5 5 5 20 1 14 9 20 1.5 19 5 20 2 23 4 20 2.5 27 4 20 3 29 2 10 0.5 3 3 10 1 7 4 10 1.5 11 4 10 2 14 3 10 2.5 17 2 10 3 19 2 5 0.5 3 3 5 1 5 2 5 1.5 7 2 5 2 9 2 5 2.5 11 2 5 3 12 2 2.5 0.5 2 2 2.5 1 2 0 2.5 1.5 3 1 2.5 2 3 0 2.5 2.5 4 1 2.5 3 4 0 Conclusion This experiment was far more accurate than the previous one, however the results were still well off what would be expected for 25vol. This leads me to believe that something else is affecting that experiment. For the second experiment all of the hydrogen peroxide concentrations were made up at the same time, so this would not have been a factor. The first three results were just about perfect, each doubling. This shows that whatever it is that is causing the change in the pattern, only affects the strongest concentrations. ...read more.

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