Measurement of Physical Properties

Dr. Nathan J. Malmberg

We will begin our study of organic molecules by measuring physical properties of several different organic compounds. These properties are frequently useful to identify and characterize organic compounds of interest. The procedure will generally follow that given in your textbook on pages 100–105, with the following modifications:

  1. Measure melting points for two different molar mixtures (more than once each) of citric acid and adipic acid, which will be assigned to you by Dr. Malmberg. The procedure for measuring melting points can be found on pages 40–42 in your textbook. Combine the data for these melting points with data obtained by the rest of the class. Graph the average melting point for each mixture as a function of mol % citric acid. Does the graph resemble the graph in Figure 4.9 in your textbook? What happens as the the sample goes from pure compound to mixture to pure compound? This is the basis of a mixed melting point determination.

    You will receive an unknown liquid of which you will determine the boiling point, density and refractive index.

  2. Obtain the boiling point (multiple determinations) on the melting temperature apparatus using the glass bell technique as outlined on pages 34–36 of your textbook.
  3. Determine the density of your sample by measuring the mass of 1 mL of your liquid (in your 1 mL syringe) on the electronic balances on the west side of the lab.
  4. Measure the refractive index of your liquid as outlined on pages 38–39 using the refractometer on the west side of the lab by the printer.

    Once you have determined the boiling point, density and refractive index of your unknown liquid, compare them to the corresponding data for the liquids listed below, as determined from the Aldrich catalog:

    • Heptaldehyde
    • Hexane
    • Methanol
    • Methylene Chloride
    • 1-octene
    • Water

    Determine the identity of your liquid unknown based on your comparison, and discuss any deviations of your measured properties from those listed in the literature.