Problem 15 - A Complete Resource Book in Chemistry for JEE Main

Question

A mixture of benzene and chloroform is separated by (a) sublimation (b) separation funnel (c) crystallization (d) distillation

Step-by-Step Solution

Answer

Distillation is used to separate benzene and chloroform.

Step 1: Understand the Mixture Type

The given mixture is a combination of benzene and chloroform, both of which are liquids at room temperature. To separate such a mixture, the method should take advantage of a property that differentiates them, like boiling point.

Step 2: Evaluate Each Separation Method

Analyze each method: - **Sublimation**: Used for solid-gas separations, not applicable as both are liquids. - **Separation Funnel**: Used for liquid-liquid mixtures that do not mix; benzene and chloroform are miscible, making this method unsuitable. - **Crystallization**: Suited for separating solids from liquids or two different crystalline solids; not applicable here. - **Distillation**: Effective for separating liquids based on boiling points; benzene and chloroform have different boiling points.

Step 3: Choose the Appropriate Separation Method

Since distillation relies on the different boiling points, and benzene and chloroform have distinct boiling points, **distillation** is a suitable method for their separation.

Key Concepts

Understanding Separation Methods

Separation methods are techniques used to separate two or more components from a mixture. These methods are heavily based on the inherent properties of substances in the mixture. Each method employs different principles to achieve separation, such as differences in particle size, density, solubility, or boiling points. When choosing a separation method, it is crucial to consider the type of mixture and the desired purity of the components. Some common separation methods include:

• Filtration: Used for solid-liquid separations; relies on particle size differences.
• Distillation: Ideal for separating liquids with different boiling points.
• Sublimation: For solids that transition from solid to gas without becoming liquid.
• Crystallization: Used to separate solid particles from a solution based on solubility differences.
• Separation Funnel: Effective for immiscible liquids that do not mix.

Selecting the right method ensures efficient and effective separation of the desired components.

Boiling Point and Its Role

The boiling point of a substance is the temperature at which it changes from a liquid to a gas. This physical property is crucial for the distillation process. In a mixture of liquids, each component has its own unique boiling point. Distillation takes advantage of these differences to separate the components one by one. During distillation, a mixture is heated until the component with the lower boiling point vaporizes. This vapor is then condensed back into a liquid and collected separately. Next, the mixture is further heated until the remaining components with higher boiling points are isolated and collected. Main points about boiling point:

• Liquids with lower boiling points evaporate first.
• Distillation separates mixtures based on these boiling points.
• Boiling points provide a clear distinction between similar yet distinct substances.

Understanding boiling points is essential for employing distillation in separating miscible liquid mixtures like benzene and chloroform.

Miscible Liquids Explained

Miscible liquids are those that can mix entirely in any proportion, forming a homogeneous solution. Unlike immiscible liquids, which separate into layers, miscible liquids do not separate and form a single-phase solution due to similar molecular interactions and energies. For example, benzene and chloroform are miscible liquids. They easily dissolve into each other, meaning traditional separation methods designed for immiscible liquids, like using a separation funnel, are ineffective. The separation of miscible liquids typically relies on properties like boiling points to achieve separation through processes such as distillation. This method efficiently separates components that form a uniform mixture. Key points about miscible liquids:

• Form a single, uniform phase.
• Do not separate on their own when mixed.
• Require methods like distillation for separation due to their uniform mixing.

Understanding the nature of miscible liquids helps in selecting the appropriate separation technique.

Significance of Physical Properties in Separation

Physical properties are observable and measurable characteristics of a substance that remain constant. They play a crucial role in selecting the appropriate separation methods for mixtures. Some common physical properties include boiling point, melting point, density, solubility, and conductivity. In separation processes:

• Boiling point: Used in distillation to separate substances like benzene and chloroform.
• Density: Determines whether a separation funnel can be used for immiscible liquids.
• Solubility: Critical in crystallization, determining which solids can be separated.

Characteristics like boiling points are pivotal in choosing methods that are efficient and suitable for specific mixtures. For a liquid-liquid mixture of miscible substances, utilizing a property like the boiling point allows for an effective separation through distillation. By leveraging the distinctive physical properties of individual components in a mixture, separation methods can be tailored to achieve optimal results.