why cant you get 100% ehtenol by distillation of the solution from the fermentation process
The correct answer and explanation is:
You cannot obtain 100% ethanol (absolute ethanol) by simple distillation of the solution from fermentation because ethanol and water form an azeotrope at about 95.6% ethanol by volume (or about 96% by weight). This azeotrope boils at a constant temperature of 78.2°C, which is lower than the boiling points of either pure ethanol (78.37°C) or pure water (100°C).
Explanation (300 words):
The fermentation process typically produces a dilute ethanol solution (about 8–15%). To concentrate the ethanol, distillation is used, which separates substances based on differences in their boiling points. As ethanol boils at a lower temperature than water, it evaporates first and can be condensed to obtain higher concentrations.
However, when the ethanol concentration reaches 95.6%, it forms a constant-boiling mixture with water known as an azeotrope. At this point, the vapor has the same composition as the liquid, so further distillation does not change the concentration. This is a unique property of azeotropes and is why simple distillation can’t yield pure ethanol.
This limitation is due to intermolecular interactions between ethanol and water molecules. Ethanol forms hydrogen bonds with water, making their separation more difficult as they approach this specific ratio.
To obtain 100% (absolute) ethanol, special methods must be used beyond distillation, such as:
- Azeotropic distillation: Adding a third substance (e.g., benzene or cyclohexane) to break the azeotrope.
- Molecular sieves: Using materials that absorb water but not ethanol.
- Vacuum distillation: Reduces pressure to alter boiling points and azeotrope behavior.
Absolute ethanol is important in industrial and laboratory settings, but for most purposes like fuel or beverages, 95% ethanol is sufficient.
In conclusion, the inability to get 100% ethanol through simple distillation is due to the formation of an azeotrope, which represents a physical limit to separation by this method.