Question

The boiling points of two miscible liquids, which do not form an azeotropic mixture, are close to each other. Their separation is best carried out by :
A) Vacuum distillation
B) Fractional distillation
C) Steam distillation
D) Redistillation

Answer 1

Hint: A substance's boiling point is the temperature at which the vapour pressure of a liquid equals the pressure around the liquid and the liquid transforms into a vapour. The boiling point of a liquid is affected by the surrounding atmospheric pressure. The boiling point of a liquid in a partial vacuum is lower than the boiling point of the same liquid at atmospheric pressure. The boiling point of a liquid at high pressure is greater than the boiling point of the same liquid at atmospheric pressure.

Complete Step By Step Answer:
The separation of a mixture into its constituent elements, or fractions, is known as fractional distillation. Heating chemical compounds to a temperature where one or more fractions of the mixture evaporate allows them to be separated. To fractionate, it employs distillation. Under one atmosphere of pressure, the boiling points of the component components should differ by no more than $ 25\text{ }{}^\circ C $ ( $ 45\text{ }{}^\circ F $ ). A simple distillation is usually employed when the difference in boiling points is larger than $ 25\text{ }{}^\circ C $ .
Consider the distillation of a combination of water and ethanol as an example. Ethanol boils at 78.4 degrees Celsius ( $ {{173.1}^{o}}F $ ), while water boils at $ \text{100 }{}^\circ C $ ( $ {{212}^{o}}F $ ). As a result, heating the combination causes the most volatile component (ethanol) to concentrate more in the vapour exiting the liquid. Azeotropes are mixes that boil at a lower temperature than either of their components. A combination of 96% ethanol and 4% water boils at $ 78.2\text{ }{}^\circ C $ ( $ 172.8\text{ }{}^\circ F $ ) in this example; the mixture is more volatile than pure ethanol. As a result, straight fractional distillation of ethanol-water combinations cannot entirely purify ethanol.
The separation of a mixture into its constituent elements, or fractions, is known as fractional distillation. Heating chemical compounds to a temperature where one or more fractions of the mixture evaporate allows them to be separated. To fractionate, it employs distillation. Because azeotropic mixtures have a fixed boiling point, fractional distillation is not possible.
Hence fractional distillation option B is correct.

Note:
The most frequent separation technology used in petroleum refineries, petrochemical and chemical plants, natural gas processing, and cryogenic air separation facilities is fractional distillation. In most situations, the distillation is carried out at a constant pace. The distillation column is constantly replenished with new feed, and the products are constantly removed. The amount of feed added and the amount of product withdrawn are generally equal until the process is disrupted by variations in feed, heat, ambient temperature, or condensing. Continuous, steady-state fractional distillation is the name for this method.