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How do temperature and concentration affect the rate of decomposition of hydrogen peroxide by the enzyme catalase?

Extracts from this document...

Introduction

How do temperature and concentration affect the rate of decomposition of hydrogen peroxide by the enzyme catalase? Aims: This is an experiment investigating how the concentration of hydrogen peroxide (substrate) and temperature affect the rate of reaction of the enzyme catalase. Introduction An enzyme is a globular protein found in living cells, they have the ability to catalyse an experiment, therefore they are often used to speed up reactions that don't happen fast enough naturally. Enzymes speed up a reaction by lowering the activation enthalpy (Ea), thus meaning that more collisions between substrate molecules and enzyme molecules result in a reaction, see fig 1 below to see how the activation enthalpy of an experiment varies in the presence of an enzyme Fig. 1: How Ea varies when a catalyst is and isn't present The graph shows that when there is no enzyme present then less of the molecules possess the activation energy so fewer collisions between particles will results in a reaction, however when the enzyme is present more of the molecules have the activation energy so more collisions results in a reaction. All enzymes are specific, they are only able catalyse one or possible a few substrates. Enzymes can recognise its substrate from even isomers, they are that specific. This is because of its three dimensional shape. Only a small part of the enzyme binds with the substrate, this is the enzymes active site. The active site is formed from a few of the enzymes amino acids. Enzymes are specific because the substrate has to fit into the enzymes active site. As the substrate enters the active site, the enzyme changes shape slightly so that the substrate fits in the active site tightly to form an enzyme-substrate complex. Weak hydrogen and ionic bonds bind the substrate and enzyme. The enzyme-substrate complex brings chemical sites from the enzyme in a better position to break down the substrate. ...read more.

Middle

Final method 1. Set up apparatus and water bath. 2. Measures out 2ml yeast with graduated pipette and put into conical flask, place resealable bung on top of flask and join up delivery tube to sidearm. 3. Measure out 4ml hydrogen peroxide into syringe and push hypodermic needle through resealable bung. 4. Inject in hydrogen peroxide and start stop clock. 5. Time for 90 seconds, measuring every 10 seconds recording results in a table. 6. Repeat 3 times for each variation of temperature and concentration. I will also carry out a titration of hydrogen peroxide; this will enable me to find out the concentration of the stock hydrogen peroxide solution (20-vol) that I am using I will be carrying out five titrations to enable me to get a reliable average for my calculations. The method for this is shown below: 1. Take 25ml of 20-vol H2O2 into a graduated flask and top up to 500 ml with distilled water. 2. Remove 25 ml of this new solution and add 200 ml of distilled water and 25 ml of sulphuric acid (1 molar). 3. Then take 25 ml of this solution into a beaker and titrate with 0.005 mol dm-3 potassium manganate from a burette, making a note of the value that the manganate solution goes up to. 4. When the solution retains its pinkish colour the titration is complete. Now take the new reading from the burette and subtract the starting volume from the end and I now have my titre. Results Below is a list of tables and graphs for each varied temperature, during these concentrations the hydrogen peroxide used always came from the stock solution (20-vol), it was not diluted: Temp- -5oC Amount of O2 collected (cm3) Time (seconds) 1 2 3 Average 0 4.0 4.0 4.0 4.0 10 8.0 7.5 4.0 6.5 20 13.0 12.0 5.0 10.0 30 20.0 16.5 10.0 15.5 40 27.5 22.0 16.0 21.8 50 31.5 27.0 21.0 26.5 60 37.0 31.5 25.0 31.2 70 42.0 35.5 29.0 35.5 80 46.5 39.0 33.5 39.7 90 49.5 43.0 37.0 43.2 Temp at end (oC) ...read more.

Conclusion

The gas is due to air displacement when we inject the hydrogen peroxide into the conical flask, we inject 4ml of hydrogen peroxide so an equal volume of air is displaced into the gas syringe. This happens for every experiment and the volume displaced is the same each time because we always add the same amount of hydrogen peroxide, therefore it doesn't alter my results or affect my graphs. One last variable that I was unable to control was the temperature of the room. As the experiments where I varied the temperature were carried out in a water bath fluctuations in room temperature wouldn't really affect them. However, the experiments where I varied concentration were carried out on the desk so these may get affected. If the room had heated up during the experiment it would have speeded up the rate of reaction due to the molecules possessing more kinetic energy, colliding more often and more of these collisions resulting in a reaction. If the temperature had of decreased then the opposite would have happened, the molecules would have less kinetic energy, less of them would possess the activation energy, so they would collide less often and less of the collisions would result in a reaction. If there were any temperature changes during my results it would make them unreliable, as the solutions would have different levels of energy. For example if there was a temperature increase at the beginning of the experiments, as I carried out the higher concentrations first the rate of these experiments would be increased. Then if the temperature went to normal the middle set of experiments would have the expected rate of reaction, and if it decreased further the last experiments I carried out would have a lower rate of reaction than expected. However I don't think that this happened because my tables of results and graphs seem to be accurate, and follow my prediction. Chemistry coursework Yr 13 Major Project Carl Ahuja Page 4 of 44 ...read more.

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