Problem 69 - A Complete Resource Book in Chemistry for JEE Main

Question

For the preparation of lyophobic colloids the methods used are normally (a) By dissolution into water (b) Condensation method (c) Dispersion method (d) Both (b) and (c)

Step-by-Step Solution

Answer

The correct answer is (d) Both (b) and (c).

Step 1: Understanding the Question

The question asks about the preparation methods for lyophobic colloids. Lyophobic colloids are typically not spontaneously formed and require specific methods for their preparation.

Step 2: Concept of Lyophobic Colloids

Lyophobic colloids are those that do not have an affinity for the solvent. Therefore, they are generally unstable and require special ions or molecules to stabilize them.

Step 3: Analyzing the Options

Let's evaluate the given options. Option (a) 'By dissolution into water' is generally not used for lyophobic colloids because they do not dissolve or disperse easily in water.

Step 4: Explanation of Condensation Method

This is a valid method for preparing lyophobic colloids because it involves the building up of particles from atoms or smaller molecules. This method is used to convert a solution into a colloidal solution by changing temperature or chemical reaction.

Step 5: Explanation of Dispersion Method

This method involves breaking down larger particles into colloidal size particles using various techniques like milling, grinding, or ultrasonic waves. It is effective for creating lyophobic colloids.

Step 6: Choosing the Correct Option

Since both the condensation and dispersion methods are relevant for preparing lyophobic colloids, both (b) and (c) are correct answers.

Key Concepts

Condensation Method

The condensation method is an essential technique used in the preparation of lyophobic colloids. This method involves building particles from smaller units, such as atoms or molecules. Instead of reducing larger particles, the condensation method starts with small, dissolved substances which are then induced to form larger colloidal particles. Typically, this method involves changing the temperature or causing a chemical reaction, promoting the aggregation of small entities into colloidal-sized particles.

Some common examples of the condensation method include:

• Reducing the solubility of substances by changing the temperature.
• Using chemical reactions to form insoluble compounds in a solution, which aggregate as colloids.

This method is particularly useful for creating stable colloids from inorganic materials, which are often hard to disperse using other techniques.

Dispersion Method

The dispersion method is another crucial approach for generating lyophobic colloids. Instead of building up particles, like in the condensation method, dispersion involves breaking down larger particles into colloidal-sized ones. This requires employing mechanical means or high-energy interventions to achieve the reduction in size.

Several techniques are used in the dispersion method:

• Grinding or milling, where large particles are physically broken down through mechanical force.
• Ultrasonication, which uses high-frequency sound waves to shear particles apart into finer, uniform colloidal particles.
• Electrical disintegration or peptization, where electrical forces are used to disperse particles in a medium.

The dispersion method is effective in creating lyophobic colloids, particularly from solid, insoluble materials.

Colloidal Stability

Ensuring colloidal stability is a significant concern in the preparation of lyophobic colloids. Such colloids are inherently unstable because they tend to aggregate and settle due to their lack of affinity with the solvent. Ensuring stability requires additional modifications or additives to maintain a stable colloidal state.

Key strategies to enhance colloidal stability include:

• Addition of stabilizing agents, such as surfactants or polymers, which create protective layers around particles, preventing them from sticking together.
• Controlling the pH of the solution, which can influence the surface charges on the colloidal particles, preventing aggregation.
• Use of electrostatic stabilization, where particles are charged to repel each other, maintaining dispersion.

Understanding how to maintain colloidal stability is essential in applications where uniform particle distribution is critical, such as in medicinal or industrial uses.