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Chemistry LibreTexts

6.1: Melting Point

  • Page ID
    93427
  • Measurement of a solid compound's melting point is a standard practice in the organic chemistry laboratory. The melting point is the temperature where the solid-liquid phase change occurs

    • 6.1A: Overview of Melting Point
      Measurement of a solid compound's melting point is a standard practice in the organic chemistry laboratory. The melting point is the temperature where the solid-liquid phase change occurs. In some reference books it is listed as a single value (e.g. 98˚C), but in chemical catalogs it is more often listed as a range of values (e.g. 96-98˚C). The melting "point" is therefore more of a melting "range," and in part, reflects how melting points are experimentally determined.
    • 6.1B: Uses of Melting Points
      There are several reasons to determine a compound's melting point: it is useful in supporting the identification of a compound, as well as serving as a rough guide to the relative purity of the sample.
    • 6.1C: Melting Point Theory
    • 6.1D: Step-by-Step Procedures for Melting Point Determination
      There are a variety of methods by which a sample's melting point can be measured, with the newest being electrical probes (e.g. Vernier MeltStation). Presented in this section are traditional methods that use an electrical melting point apparatus and Thiele tube. Both methods use capillary samples that are prepared in the same manner.
    • 6.1E: Mixed Melting Points
      As previously discussed, there are a large number of compounds that have coincidentally identical melting points. Therefore, caution should be used in identifying a compound based solely on matching the literature melting point. However, mixed melting points offer an ability to almost certainly identify an unknown compound.