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To examine the effect of Substrate Concentration (Hydrogen Peroxide) on the rate of an enzyme catalysed reaction.

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To examine the effect of Substrate Concentration (Hydrogen Peroxide) on the rate of an enzyme catalysed reaction. The reaction I will therefore study is H2O2 � 1/2 O2 + H2O Catalase Catalase is a very useful enzyme to use as it occurs naturally in the body tissues of plants and animals and catalyses the decomposition of Hydrogen Peroxide to oxygen gas. When the enzyme catalase reacts with hydrogen peroxide oxygen gas is evolved from the reaction. Therefore I am going to compare the rate at which oxygen is produced at different substrate concentrations using the catalyse enzyme to catalyse the reaction to see the effect that changing substrate concentration has on the rate of reaction. The substrate I will use is hydrogen peroxide and the enzyme I will use is catalase. Apparatus Bench mat, goggles, 250 cm3 conical flask, 100cm3 beaker, bung and delivery tube, graduated pipette, gas syringe, syringe, 10 volume hydrogen peroxide, buffer solution, distilled water, stand, boss and clamp, water bath, water, potato- source of catalyse enzyme, size 6 potato borer, knife, ruler, tile, thermometer, stopwatch. The apparatus will be set up as shown in the diagram below. 1. Before I use this equipment I need to ensure that it is completely airtight and that no gas will escape so that the gas that is produced by the reaction remains in the system and is measured by the gas syringe. If gas escapes then the full volume of gas will not have been measured and so it will not be a fair test. ...read more.


Another pre-test that I will do is following my proposed method once through for a check that the amounts of substances, equipment and timings chosen are sufficient for me to be able to carry out the experiment and obtain an answer for the brief. This is the point whereby I will make any necessary amendments to my procedure before I continue. The results I obtain will be of oxygen evolution (cm3) over 180 seconds for each substrate concentration. These will have been recorded in a table. I will calculate an average using the mean where repetitions have been carried out. Then I will plot graphs of oxygen evolution against time. It is then necessary to draw lines of best fit for each set of results and mark them with a key. From here I will obtain values for the rate of reaction by measuring the gradients of each of the graphs to allow me to plot a separate graph showing the rate of reaction against concentration. This final graph will allow me to compare all my results and will enable me to answer my brief, as it will show the actual effect of changing concentration against the rate of reaction. To obtain these gradients from the evolution/time graphs it is necessary to draw a line against the curve of the graph where it beings to level off. I will then draw two more lines on each one, one vertical and one horizontal to form a triangle so I can see exactly how much oxygen was produced over a set period of time. ...read more.


It is very unlikely that pH will affect my experiment. However I am going to make precautions. I have substituted 1cm3 of buffer solution for 1 cm3 of water where water is needed to dilute the hydrogen peroxide to its specific concentrations for use in the experiment. The buffer will stop any changes in pH. Where the buffer cannot be used i.e. where a concentration of 100% hydrogen peroxide is needed and buffer cannot be added- (as it would effectively dilute the solution) I will use litmus paper just to maintain that pH is correct at the beginning of the experiment. These are all the variables I feel that need to be controlled. I have decided to record my results at 20 second intervals, these are regular intervals so that it is easier for me to compare my results. It is important that the results are obtained at the same frequency so I can see how oxygen evolution occurs across the whole experiment. Obtaining results at shorter intervals I feel would be too hard to achieve as there would not be enough time to monitor oxygen evolution properly at this speed and the reaction will not occur so fast that a shorter interval time would give a greater degree of accuracy. Similarly if the time gap between results is too large I will not be able to monitor how the oxygen evolution varies with obtaining only a couple of readings. Therefore I deem 20-second intervals sufficient for this experiment. In the pre-test if this theory proves to be wrong and the time intervals needs altering I will be able to change them more accordingly. ...read more.

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