Azeotropic Mixture?

[ipodtouch]

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I am wondering exactly what an Azeotropic mixture is.

I tried googling it, but am unclear.
It seems to be a mixture that does not change in composition when distilled because all components have the exact same vapor pressure?

 

[syoung]

I think you're on the right track.
As a result of forming an azeotropic mixture, it cannot be completely separated by fractional distillation
When you fractionally distill a mixture, if the mixture becomes either higher in BP than the one of the constituents or lower in BP, it is now an azeotropic mixture.
As you boil a mixture, if the 2 solvents can reach an azeotropic mixture, then as you distill the mixture, the distillate will reach closer in composition to the azeotropic mixture than what you started with.

 

[MedPR]

I am wondering exactly what an Azeotropic mixture is.

I tried googling it, but am unclear.
It seems to be a mixture that does not change in composition when distilled because all components have the exact same vapor pressure?

I don't know the exact definition, but I think the relevance is that certain mixtures (azeotropes) will result in a higher or lower BP than the pure substances in the mixture. If this happens, you can't use distillation to separate the mixture.

If this pops up on the MCAT I don't think it will be a hard question because it's an exception to the rule and will probably just be a single conceptual question from a passage.