Antibiotics in Action

    Demonstration
    Peroxide Catalysis
    And Activated Complex Formation

    Major Chemical Concept

    Catalysts speed up chemical reactions, but they are not consumed in the reactions they speed up. This demonstration shows a reaction that is visibly faster when catalyzed and shows the recovery of the catalyst.
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      General Safety Guidelines
      Materials and Apparatus
      Directions
      Discussion
      Relevant National Science
      Education Standards
      Relevant New Jersey State
      Science Education Standards

    Materials and Apparatus

      0.3 M potassium sodium tartrate (Rochelle's salt) solution, 600 ml (50.8 g KNaC4H4O6·4H2O per 600 ml solution)

      6% hydrogen peroxide solution, 200 ml (Use Clairoxide® hair developer (6%), available from drug stores, supermarkets, or beauty supply companies)

      0.3 M cobalt(II) chloride, 30 ml (2 g CoCl2·6H2O per 30 ml solution)

      3 Beakers, 600 ml

      2 Beakers, 30 ml (50-ml beakers will suffice)

      2 Watch glasses large enough to cover 600-ml beakers

      3 Thermometers

      Hot plate, large

    Directions

    1. To each 600-ml beaker add 200 ml potassium sodium tartrate solution and 65 ml 6% hydrogen peroxide solution.

    2. Cover each beaker with a watch glass and heat on the hot plate until the temperature is between 65°C and 70°C. Do not exceed this temperature. While the large beakers are heating, divide the 30 ml cobalt chloride solution equally between the two smaller beakers.

    3. Add one 15-ml portion of cobalt chloride solution to one of the larger beakers, cover and observe. Keep the second sample of cobalt chloride solution plainly visible as a color comparison; have students note the color of the original cobalt chloride solution (pink).

    Discussion

    Catalysis is demonstrated by the vigorous reaction in the beaker containing the CoCl2 catalyst. The foaming is due to production of CO2(g) bubbles. The other, uncatalyzed beakers show little or no visible bubbling. Activated complex formation is demonstrated by the color change from pink to green; the green color indicates production of a Co(III) complex, although that is not the activated complex. (Activated complexes typically exist for too brief a time to be observable.)

    When the reaction is complete (no more bubbling), the catalyst is regenerated. This is shown by formation once again of pink color, indicating the regeneration of the (pink) CoCl2 catalyst. To emphasize that the catalyst has been regenerated, add a small amount of spent solution to the second 600-ml beaker, cover with a watch glass, and observe. You will note a repeat of fairly rapid bubbling, as well as formation of new green product in this second beaker. The third beaker serves as a control to demonstrate the slowness of the uncatalyzed reaction.

    Relevant National Science Education Standards

      Unifying Concepts and Processes — The demonstration involves understanding the interaction of reactants and catalysts in a reaction system.

      Physical Science — The demonstration centers on a chemical reaction.

    Relevant New Jersey State Science Education Standards

      5.1 The demonstration involves understanding the interaction of reactants and catalysts in a reaction system.
      5.8 The structure and behavior of matter at the molecular level and at the level of molecular organization are central to the demonstration.

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