Antibiotics in Action

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    Chemistry Activity
    Molecular Size
    Oleic Acid Monolayers

    Major Chemical Concept

    Molecules are mind-bogglingly small, yet their dimensions are finite and measurable. What's more, molecular size affects the physical, chemical, and biological behavior of a compound.
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      General Safety Guidelines
      Major Chemical Concept
      Teacher Notes
      Materials and Apparatus
      Relevant National Science Education
      Standards
      Relevant New Jersey State Science
      Education Standards

    Teacher Notes

    In this experiment, dust is added to the surface of the water to visualize the extent of the oleic acid layer on the water. As the solution is added, the ethanol evaporates, leaving a monolayer of pure oleic acid on the surface. By calculating the volume of pure oleic acid dropped on to the surface and the area covered by the acid, it is possible to calculate the thickness of the monolayer using the equation:

    V = (p)(r2)(h)

    1. The tray for the water should be at least 20-30 cm in diameter. If round pizza trays are not available, you can make shallow containers by lining the bottom of a cardboard box with aluminum foil or black plastic.

    2. The powder can be either lycopodium powder, eraser dust from a chalkboard, or sulfur. Small cloth bags can be made and filled partially with the dust.

    3. The oleic acid solution is typically a 0.5% solution. This is equivalent to a 0.0177 M solution. To make 100 ml of this solution, add 0.6 ml of pure oleic acid to 99.4 ml of water.

    4. The water and the acid may be disposed of in the sink when the experiment is complete.

    Materials and Apparatus

      Aluminum foil
      Ruler
      Balance
      Pizza pan
      Medicine dropper
      Beral® pipettes
      Oleic acid solution
      Powder

    Relevant National Science Education Standards

      Unifying Concepts and Processes — This experiment examines the interactions of the components of a molecular-level system. The observed behavior is explained in terms of a monolayer model.

      Science as Inquiry — The activity involves conducting systematic observations, interpreting and analyzing data, drawing conclusions, and communicating results.

      Physical Science — The structure of matter at the molecular level and at the level of molecular organization is central to the activity.

    Relevant New Jersey State Science Education Standards

      5.1 The activity involves conducting systematic observations, interpreting and analyzing data, drawing conclusions, and communicating results.
      5.3 The activity is mathematical in nature.
      5.6 The structure and behavior of matter at the molecular level and at the level of molecular organization are central to the activity.

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