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Decomposition of Hydrogen peroxide

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Decomposition of Hydrogen peroxide SCIENTIFIC BACKGROUND INFORMATION I will investigate the factor that affect rate of reaction of the enzyme catalase. Catalase is an enzyme found in living cells i.e. potato and liver. It promotes the conversion of hydrogen peroxide a powerful and potentially harmful oxidising agent to water and molecular oxygen (the enzyme increases the rate of decomposition of hydrogen peroxide into water and oxygen). The reaction is: - 2H O --> 2H O + O Enzymes are biological catalysts that increase the rate of a reaction. The reactant substances upon which an enzyme acts are termed the substrates. The substances produced as a result of the reaction are the products. Enzyme-controlled reactions are mostly reversible and involve the formation of an intermediate enzyme-substrate complex. Activation energy In order to start a reaction, chemical bonds must be broken so that new bonds can be formed. The energy necessary to break these bonds is the activation energy of the reaction. The graph below shows changes, which will take place when hydrogen peroxide breaks down to produce water and oxygen. One way in which we can provide the activation energy to start this reaction is to add an enzyme (catalase) Catalase lowers the activation energy and, as a result, the reaction will take place at the much lower temperatures found inside the cells of living organism Catalase will speed up the process because the enzyme lowers the activation energy of the reaction. This means that the free energy required for the reaction to take place will be made smaller by the presence of catalase. In fact, catalase is particularly reactive enzyme. ...read more.


When all the active sites are occupied and the amount of enzyme is the limiting factor, as you increase the amount of the substrate there are more collisions and more enzyme- substrate complexes formed. If the temperature increases, it can affect the rate of an enzyme-controlled reaction in two ways: (1) As the temperature increases, the kinetic energy of the substrate and enzyme molecules increases and so they move faster. The faster these molecules move, the more often they collide with one another, and therefore the rate of reaction is faster. In addition, the more often they collide more enzyme- substrate complex is formed and more products are released. (2) As the temperature increases, the more the atoms, which make up the enzyme molecules, vibrate. If they vibrate, too much it will break the hydrogen bonds and other forces, which hold the molecules in their precise shape. The three-dimensional shape of the enzyme molecules is altered so much that their active sites no longer fit the substrate. The enzyme will be denatured and loses its catalytic properties. The optimum temperature for an enzyme varies considerably, depending on its surroundings. For many enzymes, the optimum temperature is 400C and denaturation occurs at 600C. Altering the pH can also break the bonds of the three-dimensional molecular shape. This is because the bonds may be broken by the concentration of hydrogen ions and pH is a measure of hydrogen ion concentration. Any change in the pH can denature enzymes. Each enzyme work best at its own particular pH (Optimum pH). Changing the size of the surface area of the potato can also alter the rate of reaction. ...read more.


had to use the same cork borer, it was very difficult to obtain a piece of potato tissue, as each time you use cork bore you had to cut it straight down, not on the side. Moreover, I had to maintain the same surface area of the potato tissue, sometimes, though; you have used the same cork bore, I difficult to have the same diameter of the potato tissue (every time to void some errors I had to cut the straight down). It was difficult to maintain the same level of temperature, as when the reaction is rapid the substrate concentration is high and energy will be released, which might have increase the temperature of the hydrogen peroxide. In addition, I should have measured first the room temperature, as this might have effect on my results. Moreover, since rates of reaction are so sensitive to temperature I still would have liked to use a water bath during this experiment, as this would have regulated the temperature. When starting the reaction by adding the hydrogen peroxide and the potato together they reacted immediately so I had to quickly put the bung in very quickly. When I was doing, this some of the oxygen may have escaped before I put the bung in. This would have directly affected my results and therefore my accuracy. I could not start the timer and put piece of potato into the hydrogen peroxide at the same time therefore the timing was a bit inaccurate. I would have been better if I had had a partner to start the stop clock for me once the potato tissue was introduced to the hydrogen peroxide. This may have improved my results slightly. ?? ?? ?? ?? Ali Ahmed ...read more.

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