chem 31.1 expt 3

1) The sample liquefies then becomes gaseous and deposits on the filter paper. When it reaches the cooler filter paper, it eventually recrystallizes into solid form. 2) The melting points are both the same at 104ᵒ 104ᵒC. Of the advantages of recrystallization, many organic compounds turn directly from the solid phase to the gaseous phase, making sublimation the only alternative. Also, since the sample goes t o the gaseous phase, it is more likely t o separate away contaminants especially those that reach only the liquid or solid phase. 3) Very few organic substances sublimate in normal atmospheric pressure, t his requires the use of a vacuum sublimation apparatus. Furthermore, the sublimation in a closed container will cause the pressure to increase as the sublimation occurs, which may cause it to stop before the desired time. 4) The sublimation can be performed at low enough temperatures that very little of one substance and none of the other is turned gaseous. In this way only the first substance is only ‘partially’ sublimed. Certainly impurities from simultaneous sublimation will occur so this process should be repeated with the collected crystals slightly purer each time.

D.Pasto, C. Johnson and M. Miller, Experiments and Techniques in Organic Chemistry , Prentice Hall, New Jersey, 1992.