In the Organic Chemistry Teaching Labs, the melting point of a compound is determined as a method of compound identification.
An organic compound’s melting point is one of several physical properties by which it is identified. A physical property is a property that is intrinsic to a compound when it is pure. Since melting points are relatively easy and inexpensive to determine, they are handy identification tools to the organic chemist.
If you want to use the melting point to identify a solid compound which you have isolated in the lab, you will need to compare its melting point with that of the true compound. Melting points are listed in various sources of scientific data, as referenced on the Chem Info page or in the physical data tables on this orgchem site:
If you look up the melting point of a compound in more than one source, you may find that the values reported differ slightly. Keep in mind that the melting point ranges listed in the company catalogues (Acros, Baker, Sigma-Aldrich, etc.) are the melting points of the compounds as they are sold. If the compounds are sold slightly impure, the melting point range will reflect this fact. The melting point listed in the CRC, Merck Index, or on the MSDS is the melting point of the pure compound. While theoretically these should be constant from source to source, in reality the reported melting points sometimes vary. Therefore:
Two types of melting point apparati are available in the Organic Chemistry teaching labs, the “Fisher-Johns” and the “Mel-Temp”. Explanations (including pictures) of how to take a melting point on each type of apparatus are linked to below:
How to Take a Melting Point 10 min 45 sec into this Crystallization movie. On GoogleVideo - choose "smoothing" and "original size" from the lower right pull-down menu for best video.
