Antibiotics in Action

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    Chemistry Activity
    Comparing Catalysts

    Introduction

    Hydrogen peroxide is a very reactive compound that can be used for a variety of reactions including bleaching and disinfecting minor wounds. Acting as an oxidizing agent, it is also toxic to cells, hence its value as a disinfecting agent that disrupts the metabolism of bacteria. Our body cells and those of many other animals contain an enzyme called catalase that accelerates the conversion of toxic hydrogen peroxide to water and oxygen gas.
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    Introduction
    Purpose
    Safety
    Materials and Apparatus
    Procedure
    Data Analysis and Concept
    Development

    enzyme-catalyzed ecomposition of hydrogen peroxide

    Enzyme activity in living cells varies according to a variety of chemical conditions. In this investigation both an inorganic catalyst (manganese dioxide—MnO2) as well as an organic catalyst or enzyme (catalase) will be tested.

    Purpose

    To study the various factors that affect the rate of a chemical reaction with and without a catalyst.

    Safety

    Wear protective goggles throughout the laboratory exercise.

      General Safety Guidelines

    Materials and Apparatus

    • Pieces of fresh (not frozen) liver, each about 6 mm in "diameter"
    • Pieces of fresh potato
    • 100 ml of 3% hydrogen peroxide
    • Manganese dioxide (MnO2) powder
    • Distilled water
    • Fine sand
    • 3 test tubes, 18 x 150 mm (preferable that they have a permanent white patch for marking with pencil)
    • 250-ml beaker
    • Test tube rack (or small beaker with paper towel padding on inside, bottom)
    • Forceps
    • Mortar and pestle

    Procedure

    1. Prepare a table similar to the one below.

      Test No. Substance Tested Reaction: fast, slow, or none?

      1

      		Sand and water  

      2

      		Sand and H2O2  

      3

      		MnO2 and water  

      4

      		MnO2 and H2O2  

      5

      		Boiled MnO2 and water  

      6

      		Whole liver and MnO2  

      7

      		Ground liver and MnO2  

      8

      		Boiled liver and MnO2  

      9

      		Whole potato and MnO2  

      10

      		Ground potato and MnO2  

      11

      		Boiled potato and MnO2  

    2. Obtain three test tubes of the same size. Using a sticky label, mark a height of 2.0 cm from the bottom of one tube. This tube will be used to measure liquids in the other two tubes. Label the other tubes A and B, using the permanent white “patch” on the tube or use a wax (“grease”) pencil. Do not use sticky labels as they will come off when placed in hot water.

    3. To tube A, add distilled water to the 2.0-cm mark. To tube B, add an equal amount of hydrogen peroxide.

    4. To each tube, add a pinch of sand. Observe for a reaction and record the results in the table for test numbers 1 and 2.

    5. To the same two test tubes, add a pinch of manganese dioxide (MnO2) powder. Observe any changes and record the rate of reaction in your table under tests #3 and #4.

    6. Place test tube A (MnO2 and water) in boiling water for 3 minutes. Add 5 cm3 of hydrogen peroxide (H2O2) to the tube. Observe any reaction and record in the table under test number 5.

    7. Clean out both test tubes. Pour fresh hydrogen peroxide up to the 2 cm mark on both tubes.

    8. Add a pinch of sand to both tubes. Using forceps or a toothpick, add a small piece of liver to the tube A. Observe and reaction and record results in the table under test 6.

    9. Obtain a second piece of liver approximating the size used previously. Put the liver in a mortar with a pinch of sand AND 2 cm3 of distilled water. Grind the liver with the pestle.

    10. Pour the liver/sand/water mix into test tube B (second tube) that contains hydrogen peroxide. Observe any reaction and record under test #7.

    11. Clean out both test tubes. Pour fresh hydrogen peroxide into tube A up to the 2-cm mark. Add a pinch of sand.

    12. Place another piece of liver into boiling water for about 5 minutes. Drop the boiled liver into tube A. Record your observations under test 8.

    13. Repeat steps 7-11 using potato in place of liver, recording results under tests 9-11.

    14. Extensions of this investigation include studying the effect of different pH values for the test solution. Will water be used separately from hydrogen peroxide as in the previous tests? Why or why not?

    Additional factors to study include temperature and concentration of the enzyme contained in the liver or potato. This is a good opportunity to design experimental procedures.

    Data Analysis and Concept Development

    1. What is the purpose of using sand in tests #1 and #2?

    2. Why add water to MnO2 in test #3? How does this relate to test #4?

    3. Relate tests #1 and #2 to tests #3 and #4.

    4. What tests give evidence that manganese dioxide is causing the hydrogen peroxide to break down instead of reacting with it to form other products besides water and oxygen gas? WRITE OUT your reasoning with evidence.

    5. What caused the reactions in tests #6 and #7? Were there differences in the RATE of the reactions between the two setups? If so, how would you explain this? What does grinding have to do with the rate?

    6. If there were differences in the rate of reaction between test #7 and #8, how would you explain this?

    7. Do tests #4, #6 and #7 imply that liver contains manganese dioxide? What other tests would provide evidence that liver could not contain manganese dioxide?

    8. Review the test results for potato, if done, and relate to the results with liver. Are there any differences? Should there be?

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