Patterns of Behaviour - Sample Essay

Aim: To find how the rate of reaction/rate of decomposition is affected by the concentration of hydrogen peroxide. Liver will be used as a source of catalase, used as a catalyst. Diagram: Hypothesis: Hydrogen is a colourless substance that is sometimes used to bleach hair. It is harmful to humans. Some cells in the body can break down harmful substances such as hydrogen peroxide into non-toxic chemicals such as water and oxygen. The equation for this is: 2H2O2(aq)–>2H2O(l)+O2(g) One of the organs that can break hydrogen peroxide down into water and oxygen is the liver, which contains catalase.

Catalase is an enzyme that acts as a catalyst. This can help to decompose Hydrogen Peroxide quickly. A catalyst is a substance that speeds reactions. The concentration of hydrogen peroxide is given as the volume of oxygen that can be obtained from one volume of the solution. For example, 10cm3 of 1 Volume hydrogen peroxide produces 10 cm3 oxygen when it decomposes. 5 Volume hydrogen peroxide will make 5 times this amount. I predict that the rate of reaction will be faster when the concentration of hydrogen peroxide is higher.

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This is because the rate of reaction will increase when there are more molecules of hydrogen peroxide freely available to be broken down into water and oxygen. The hydrogen peroxide will break down into oxygen and water in the presence of Catalase. If there are more molecules of Hydrogen peroxide (eg a higher concentration) more oxygen will be produced in one minute. The rate of reaction will be higher. Method: 1. Measure out 10mls of 5 Volume Hydrogen peroxide. Place this in a conical flask. 2. Add a small piece of liver (around the size of a grain of rice) to the hydrogen peroxide as a source of catalase.

Catalase is used as a catalyst for the decomposition of Hydrogen peroxide. 3. Seal the conical flask immediately (to prevent oxygen escaping) using a bung connected to a gas syringe. 4. Start the stopclock immediately and time for one minute. 5. Measure and record the amount of Oxygen collected in the gas syringe after one minute. This will show the rate of reaction. 6. Repeat steps 1-5 to test the results. This will minimise the extent of any inaccuracies, as the results can be averaged. 7. Repeat steps 1-6, using 10 Volume, 15 Volume and 20 Volume Hydrogen peroxide.

Record results in a table and a graph. Variables I will be varying the concentration of the hydrogen peroxide used in this investigation. I will keep the investigation fair by controlling other variables in the experiment. Other variables are: 1. Temperature-As temperature increases, the rate of reaction is affected as the particles are given more energy. This causes the molecules to move faster (kinetic theory). As the breaking down of hydrogen peroxide is exothermic, the mixture will be heated up, therefore the particles will move faster and the heat gives them more energy.

Also, as the temperature continues to rise it may affect how the catalase enzyme works, and could possibly denature it. I cannot control how much heat energy is given out when the Hydrogen peroxide decomposes, although the temperature around the investigation will remain fairly constant, at room temperature of around 20i?? C. 2. Concentration of catalase-Although this is not easily controlled (as the amount of liver is not easy to measure), I try to use the same amount of liver in each experiment. Other things that will affect the results o the experiments are: Oxygen escaping when the liver is first added to the hydrogen peroxide.

-Gas escaping from the gas syringe. -Inaccurate reading of results. -The stopclock not being started at the same point in each experiment. Apparatus required: 1. Conical Flask-where the decomposition of hydrogen peroxide takes place. 2. Hydrogen peroxide of concentration 5 volume, 10 volume, 15 volume and 10 volume. 3. Liver-used as the source of catalase for this experiment. 4. Bung with delivery tube-To seal the conical flask and collect oxygen gas produced during the decomposition of hydrogen peroxide. 5. Gas syringe-Measures the amount of oxygen produced. 6. Stopclock-Times 1 minute so that we can calculate the rate of reaction.

Risk analysis Hydrogen peroxide is used as a bleach, so it will be handled very carefully. Results The table overleaf shows my results from this investigation. I took two readings each time to gain a better picture of my results and so that I could see whether there were any anomalous results. On the whole, I am pleased with my results although some seem to be a little anomalous. To test my hypotheses I shall draw a graph with lines to show the rate of reaction for each experiment in the investigation.

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