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.
The reason it is difficult to completely separate ethanol (ethyl alcohol) from water is because of their chemical properties and the type of bonding they form. Ethanol and water are both polar compounds, meaning they have regions with partial positive and negative charges. This polarity allows them to mix together and form hydrogen bonds.
Hydrogen bonding occurs between the hydrogen atom of one molecule and the oxygen atom of another molecule. In the case of ethanol and water, the oxygen atom in water can form hydrogen bonds with both the oxygen atom and the hydrogen atom in ethanol.
When a mixture of ethanol and water is heated, the two compounds can evaporate together as a mixture. This process is called distillation. However, the boiling points of ethanol and water are close (ethanol boils at 78.4°C and water boils at 100°C), which means that at a certain temperature, both compounds will turn into vapor simultaneously, making it difficult to separate them completely.
To separate ethanol from water with higher precision, a technique called fractional distillation is used. Fractional distillation takes advantage of the difference in boiling points by using a fractionating column that provides multiple condensation and evaporation stages. By carefully controlling the temperature and condensation processes, it is possible to achieve a higher degree of separation. However, completely removing all traces of ethanol from water is challenging due to their similar boiling points and strong hydrogen bonding.