Is it possible to obtain pure (200- proof) ethanol using fractional distillation from a fermentation mixture that contains equal amounts of water and ethanol? why or why not?
No, because water and ethanol form what is called an azeotrope.
No, it is not possible to obtain pure 200-proof ethanol using fractional distillation from a fermentation mixture containing equal amounts of water and ethanol.
Fractional distillation is a process used to separate liquids with different boiling points. In this case, ethanol and water have different boiling points, with ethanol boiling at approximately 78.4 degrees Celsius and water boiling at 100 degrees Celsius. However, achieving 200-proof ethanol requires the complete removal of water, which is challenging because water forms a constant azeotrope with ethanol at a composition of roughly 95% ethanol and 5% water.
During fractional distillation, vapor from the boiling liquid mixture rises through a fractionating column. The column contains several trays or packing material that act as surfaces for condensation and vaporization. The vapor becomes enriched in the lower boiling component (ethanol), while the liquid at the bottom becomes enriched in the higher boiling component (water).
However, in the case of the ethanol-water mixture, once the vapor reaches a composition of around 95% ethanol and 5% water, it becomes increasingly difficult to further separate the two components using fractional distillation. This is because the azeotrope formed by ethanol and water has a lower boiling point than pure ethanol (approximately 78.2 degrees Celsius), making it impossible to achieve pure 200-proof ethanol using this method.
To obtain higher purity ethanol, additional techniques such as molecular sieves, azeotropic distillation, or dehydration agents like calcium oxide or molecular sieves can be employed to remove the remaining water content and achieve 200-proof ethanol.