Purification by Fractional Distillation

Fractional distillation column at an oil refinery


As chemists, we often need to separate and purify mixtures of molecules. When we synthesise new chemicals, we rarely make one pure product without side products or unreacted starting materials or catalsyts that are present in the mixture with the product. We don’t always make new compounds that need separating, sometimes we wish to extract naturally-occuring molecules from mixtures.

There are several ways to separate different chemicals from one another, and the purification of molecules is often the hardest part of a chemist’s job!

If we wish to separate a mixture of liquids, we can use the fact that they have different boiling points.


fractional distillation column


A pdf version of this experiment is available here. Please ensure you refer to the safety card. Details for teachers or technicians can be found here.


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distillation setup (on a hotplate)



  • Conical flask
  • Rubber bung with 2 drilled holes
  • thermometer
  • plastic/teflon tubing
  • 6-8 test tubes and rack
  • beaker
  • fizzy drinks (fizzy orange works well, it is good to compare diet and standard versions of the same drink)


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