[Invincible]

Water and alcohol forms an azeotrope where the blend will carry over with the vapor having the same concentration as solution at all times. The azeotrope is 96%/4% by weight.

From reading through wikipedia, if the starting concentration has more EtOH than azeotrope, the final product will be slightly higher in ethanol than azeotrope and slightly below if its below azeotrope to start.

Suppose you are distilling 50/50 blend of water ethanol, but the final product sought after is the water.  What is the maximum purity of water achievable here and how do we know this?

[fledarmus]

And what is your reasoning so far? When you start raising the temperature in your flask of EtOH/Water, what will the first drops distilled off consist of?

[Invincible]

The first drop is not pure, but it is richer in ethanol.  It takes multiple distillations to even get to azeotrope.

Source cited in wiki says if said solution was distilled, it will be 80% EtOH the first pass.
Distill the distillate again to yield  87% and repeated will get asymptotically close to 95.5% EtOH.

This will tell you how much higher BP component gets carried over to the distillate(in this case 4.5% ethanol carried over to final product after repeated distillations).  

I am assuming that its not completely possible to completely rid of ethanol through distillation. Let's suppose this is to purify water by distillation which includes ethanol as contaminant.  

Is the water in ethanol azeotrope documented above different from ethanol in water azeotrope?  

[Hunter2]

To get 100% Ethanol Cyclohexane is added as a 3 mixture. In an rectification process you get the Ethanol first and an azeotrop of water and Cyclohexan, what will have phase seperation after cooling down.

http://www.google.com/url?sa=t&source=web&cd=3&ved=0CCgQFjAC&url=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FEthanol&rct=j&q=ethanole&ei=Q4w6Tu6OCoS3hQfuvOH7AQ&usg=AFQjCNHhavcULjVvWC-KgHBmyY_603LigQ&sig2=-hOjgJu13pw4Be0lziWBog&cad=rja

[fledarmus]

Source cited in wiki says if said solution was distilled, it will be 80% EtOH the first pass.

This is enough information. If you get 80% ethanol as your distillate, what is left in the flask?