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.

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BIOLOGY INVESTIGATION PLAN-

INVESTIGATING THE DECOMPOSITION OF HYDROGEN PEROXIDE

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. 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.

  1. 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.

  1. Seal the conical flask immediately (to prevent oxygen escaping) using a bung connected to a gas syringe.
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  1. Start the stopclock immediately and time for one minute.

  1. Measure and record the amount of Oxygen collected in the gas syringe after one minute. This will show the rate of reaction.

  1. Repeat steps 1-5 to test the results. This will minimise the extent of any inaccuracies, as the results can be averaged.

  1. 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 ...

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