Is it possible to obtain pure (200-proof) ethanol using fractional distillation from a fermentation mixture that contains equal amounts of water and ethanol? Explain your answer.

I know that some water will still remain i would just like to know why some water vapor will be present at the low bp of ethanol.

The reason is that there is a vapor pressure present in water in any temp, even at room temp.

http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/watvap.html

When it comes to obtaining pure (200-proof) ethanol using fractional distillation from a fermentation mixture that contains equal amounts of water and ethanol, it is not possible to completely remove all the water.

During fractional distillation, the liquid mixture is heated, and the vapors that are produced are collected and cooled down to condense into liquid form. The basic principle behind fractional distillation is that substances with lower boiling points vaporize and separate from substances with higher boiling points.

In the case of ethanol and water, ethanol has a boiling point of around 78.4 degrees Celsius (173.1 degrees Fahrenheit), while water has a boiling point of 100 degrees Celsius (212 degrees Fahrenheit). Therefore, when the fermentation mixture is heated, the ethanol will vaporize first, and primarily ethanol vapors will be collected.

However, due to the azeotrope formation between ethanol and water, it is not possible to completely separate the two substances using fractional distillation alone. An azeotrope is a mixture of liquids that boils at a constant temperature, resulting in a vapor mixture with the same composition as the original liquid mixture.

In the case of ethanol-water mixtures, an azeotrope is formed at approximately 95.6% ethanol by mass, which has a boiling point lower than that of pure ethanol. This means that even after fractional distillation, the highest concentration of ethanol that can be obtained is around 95.6%.

To achieve higher concentrations of ethanol, additional processes such as molecular sieves, dehydration agents (like calcium oxide or molecular sieves), or further distillation using specialized equipment are required. These processes can help remove more water and achieve higher concentrations, but it is extremely challenging to reach 100% ethanol purity.

Therefore, while fractional distillation can separate a significant portion of ethanol from a fermentation mixture containing equal amounts of water and ethanol, it is not possible to obtain pure (200-proof) ethanol solely through this method.