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

(d) Both (b) and (c)

Step 1: Understanding the Question

The question asks about the methods employed in the preparation of lyophobic colloids. Lyophobic colloids typically repel liquids and don't easily form solutions.

Step 2: Examining Each Choice

Let's analyze each option: 1. (a) By dissolution into water - This is more relevant to lyophilic colloids, which easily blend with the solvent, typically water. 2. (b) Condensation method - This involves vapor phase to liquid or a chemical reaction leading to precipitation which can be applicable to lyophobic colloids. 3. (c) Dispersion method - It involves breaking down larger particles into colloidal size using mechanical dispersion or peptization which is applicable to lyophobic colloids. 4. (d) Both (b) and (c) - This states that both the condensation and dispersion methods are used.

Step 3: Selecting the Correct Answer

Since lyophobic colloids do not form solutions through mere dissolution, methods such as condensation and dispersion are relevant. Hence, option (d) which combines both (b) and (c) is suitable for the preparation of lyophobic colloids.

Key Concepts

Condensation Method

In the world of chemistry, the condensation method is an essential technique used to form lyophobic colloids. Lyophobic colloids, unlike their lyophilic counterparts, have a natural tendency to repel liquids. This characteristic makes them challenging to dissolve under regular conditions. The condensation method involves transforming either gas or liquid into smaller particles by forming a new phase.
This can occur through chemical reactions where new molecules are produced, eventually forming a colloidal solution. A typical approach is to start from a molecular state and let the particles grow until they reach a colloidal size.

• Chemical reactions: Various chemical reactions can induce the formation of solids from solutions, such as forming sulfur sol from hydrogen sulfide gas.
• Vapor phase to liquid: This includes processes like cooling vapors until they condense and form tiny particles.

By understanding this method, students can appreciate how essential science principles help create substances with particular physical properties.

Dispersion Method

The dispersion method is another fundamental approach in the formation of lyophobic colloids. In contrast to the condensation method, where particles are built up, dispersion involves breaking down larger particles into smaller, colloidal-sized particles. Traditionally, this can be achieved through mechanical means or other dispersion techniques.
Key dispersion techniques include:

• Mechanical dispersion: Processes like grinding, stirring, or ultrasonication break down larger particles into colloidal sizes.
• Peptization: This involves stabilizing and breaking down aggregates into individual colloidal particles using an electrolyte.

These techniques are particularly beneficial when handling substances that naturally resist forming a suspended solution. By breaking them down, the particles can remain dispersed in the medium, granting the material its colloidal properties.

Colloidal Preparation

Colloidal preparation is a crucial step in creating lyophobic colloids, which naturally do not dissolve easily. Both the condensation and dispersion methods provide key approaches for achieving colloidal solutions of lyophobic materials.
To prepare such colloids successfully, one must consider:

• The nature of the substance: Some materials may respond better to one method over the other.
• Desired particle size: The size of the particles can determine their stability and the method chosen.
• Stability: Ensuring that the colloids do not aggregate and settle is paramount, often requiring stabilizers.

By employing these methods thoughtfully, scientists and students alike can create colloids with specific and beneficial properties, expanding their application range significantly in various industries.