Why would it not be possible to obtain 100 % pure ethanol through a distillation of an ethanol mixture?

Answer 1

I assume that you mean and ethanol/water mixture since there is only a single chemical called ethanol (CH3-CH2-OH).

Ethanol and Water form an azeotropic (see 2) mixture at 96% EtOH. This means both water and Ethanol will boil at exactly the same temperature and have the same ratio (96:4) in both liquid and vapour form.

Since distillation is the separtion of liquids by getting one liquid into vapour form more easily than the other it will fail.

See link 2 for information on how to break the azeotrope.

Answer 2

Because at the boiling point (around 78°C) of the mixture of ethanol with water (which is the universal solvent of many compounds) it is formed a mixture called "azeotrope" that can not be separated in its individual components just by distilation.

The "most pure" ethanol you can get from simple distillation is at 96%

One way to separate an azeotrope is for example adding salt to the boiling vessel in order to elevate the boiling point of water and getting more pure ethanol.

Good luck!

Answer 3

because water-ethanol forms an azeotrope somewhere around 96% alcohol

that means that the vapor pressure of the alcohol and the water at that mixture is such, that just distilling will not change the ratio of water and alcohol

whatever you boil off will come of in that same mixture, and the concentration in the liquid will not change

the wikipedia has a nice article on azeotropes
http://en.wikipedia.org/wiki/Azeotrope

there are, of course, ways to deal with azeotropes
you can add a third componant that will make for a different distillation limit

or you can use a separation technique other than distilation

Answer 4

think its due to it being a hydrocarbon, or organic chemical. de-ionising water is a little different cos it aint an organic chemical.