[mandy]

Can a azeotropic mixture be separated by fractional distillation (consider the purity of the origional samples)?  An azeotropic mixture is a solution whose vapours have the exact composition of the original solution.  Because of this, an azeotropic mixture behaves like a pure liquid and cannot be separated.  I think this is for a normal distillation, but what about a fractional distillation?

Fractionating columns normally work better if they are insulated.  This helps to maintain a smooth temperature gradient in the column.  Why is it important to maintain a uniform temperature gradient in a fractionating column?  So i understand that it is to prevent heat loss but why is it so important that the column stays hot?

[alphahydroxy]

Nope - afraid you can't separate aezoptropic mixtures through fractional distillation over a simple distillation. IIRC, a fractional distillation setup has a much greater number of theoretical plates, and this is the reason it is used to separate compounds with very close boiling points. An azeotropic mixture behaves, as you mentioned, as a pure liquid and thus cannot be separated in this manner. There are ways to separate azeotropes however, this article goes over the essentials:

http://en.wikipedia.org/wiki/Azeotrope


The reason the distillation goes better if the column is insulated is really a practical thing. Remember, essentially, you want the liquid to become a vapour and travel up the column before condensing in the actual condensor and being collected. This is facilitated by the column being isothermal, as a particular fraction can travel up the column at a particular tempearature, without having to condense and drop back down as it reaches a cold spot nearer the top.

[mandy]

Thanks for your help - good explinations, I appreciate it