Question

Azeotropic mixture of two liquids can be separated by: (a) Azeotropic distillation (b) Fractional distillation (c) Simple distillation (d) Steam distillation

Short answer

(a) Azeotropic distillation

Step-by-step solution

Understand Azeotropic Mixtures

Azeotropic mixtures are special combinations of liquids that affect boiling points. At a certain composition, they boil at a constant temperature and behave like a pure substance.

Identify the Separation Technique

To separate a mixture where components have the same boiling point (as in an azeotrope), standard distillation techniques are insufficient. However, azeotropic distillation involves the addition of a third substance or other methods that break the azeotropic composition.

Examine Provided Options

The question provides four options: azeotropic, fractional, simple, and steam distillation. Azeotropic distillation is specifically designed to break or shift the azeotropic conditions and separate the liquids.

Choose the Best Option

Since azeotropic distillation is aimed explicitly at separating azeotropic mixtures by altering or disrupting the azeotrope, it stands out as the correct choice among the options.

Key concepts

Azeotropic Distillation

Azeotropic distillation is a specialized method used to separate azeotropic mixtures, which are unique combinations of liquids with identical boiling points at certain compositions. These mixtures behave like pure substances, making them challenging to separate using standard distillation methods.
Azeotropic distillation involves adding a third substance, known as an entrainer, to the mixture. The purpose of the entrainer is to alter the boiling point conditions, thereby disrupting the azeotrope. This method can also include pressure-swing distillation, where the pressure of the system is manipulated to change the azeotropic point and facilitate separation.

• The addition of an entrainer helps in creating a new azeotrope for one of the components.
• It's useful when it comes to separating complex mixtures that can't be handled through simple distillation.

By leveraging these techniques, azeotropic distillation succeeds in breaking the azeotropic conditions, allowing for the effective separation of components.

Separation Techniques

When faced with the challenge of separating a mixture of liquids, especially an azeotropic mixture, understanding the right separation technique is crucial. Traditional methods, such as simple distillation, rely on the difference in boiling points to separate liquids.
However, when components boil as a single entity at a distinct constant temperature, more advanced separation techniques must be utilized. Here are a few techniques explained:

• Azeotropic Distillation: Involves altering the azeotropic conditions using an additional compound, designed primarily for azeotropic mixtures.
• Fractional Distillation: Utilizes a fractionating column to separate components with slightly different boiling points by repeated vaporization-condensation cycles.
• Steam Distillation: Useful for temperature-sensitive components, where steam is used to lower boiling points and avoid decomposition.

Choosing the right technique depends on the nature of the mixture and the desired outcome.

Boiling Points

Understanding boiling points is key when it comes to separating mixtures. The boiling point of a liquid is the temperature at which its vapor pressure equals the external pressure, often atmospheric pressure.
Azeotropic mixtures are peculiar because, at a specific composition, they have a constant boiling point and behave as if they were a pure compound. This characteristic makes separation a complex task.

• Azeotropes can come in two main types: minimum boiling (with a lower boiling point than its components) and maximum boiling (with a higher boiling point).
• They defy standard distillation methods because the components vaporize in the same ratio as the liquid mixture.

By focusing on boiling points, chemists can tailor their approach, utilizing techniques like azeotropic distillation to tackle these challenges.

Fractional Distillation

Fractional distillation is a classic technique used to separate liquid mixtures into individual components with different boiling points. It's more effective than simple distillation when components of the mixture have boiling points that are fairly close to each other.
In this process, a fractionating column is used, which provides increased surface area for multiple vaporization-condensation cycles. This ultimately enhances the separation efficiency by allowing each component to distill off at its respective boiling point.

• As the mixture is heated, components with lower boiling points vaporize first and rise through the column.
• The repeated cycles ensure better purity and separation of the components.

Although fractional distillation is not suitable for breaking azeotropes, it remains an essential tool in the separation of less complex mixtures.