posted by Tim .
why is it impossible to completely separate ethanol from water?
Because water and ethanol form an azeotrope at approximately 95%ethanol/5% H2O. Those aren't exact figures but they are within 1% of the right values.
Everything I said in the above response is correct. What I did not say, your post says "impossible" to completely separate H2O/ethanol. That implies that it is not possible to prepare 100% ethanol which isn't true. 100% ethanol is available on the open market and has been for years and years.