Question

Student in O-Chem Lab conducts a melting point experiment with an unknown compound and observes a melting range of 210 – 218C. Is this a typical range for a melting point? If not, what range would be typical?

For this question, does it mean an unknown compound in general? I am thinking that this melting point is sort of typical depending on what the unknown compound is. I don't know if that reasoning is correct tho.

Answer 1

No, the reasoning is not correct. PURE compounds have a melting point range of a few tenths of a degree to perhaps as much as 2 degrees. Generally, the purer the compound the smaller the range. A range of 8 degrees is not typical of a pure organic compound and tells you immediately that the unknown is not a pure substance. Here is a site that talks about the range a little. Note the remark that the melting point can NOT be higher than the literature value since impurities LOWER the melting point.
http://www.csi.edu/ip/physci/faculty/rex/MPTips.htm