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 Lyophobic Colloids

Lyophobic colloids are systems in which the dispersed particles do not have an affinity for the dispersion medium. This is different from lyophilic colloids, where the dispersed particles do attract the dispersion medium.

Step 2: Exploring Preparation Methods

Two main methods are used to prepare lyophobic colloids: the Condensation method and the Dispersion method. The Condensation method involves bringing together smaller molecules or ions to form larger particles. The Dispersion method involves breaking down larger particles into colloid-sized particles.

Step 3: Analysis of Given Options

Let's analyze each of the options provided: (a) refers to a method unsuitable for lyophobic colloids, as they don't dissolve well in water. (b) and (c) refer to the Condensation and Dispersion methods, respectively, both of which are used for preparing lyophobic colloids.

Step 4: Selecting the Correct Answer

Based on the understanding that lyophobic colloids can be prepared by both Condensation and Dispersion methods, the correct choice includes these two methods.

Key Concepts

Condensation Method

The condensation method is a fascinating approach used to create lyophobic colloids by assembling smaller molecules or ions into larger, colloidal-sized particles. This transformation happens through chemical reactions that result in the creation of new bonds. For example, in a chemical reaction where vapor molecules come together to form droplets, a condensation process is taking place.
Condensation methods can occur through processes like oxidation, hydrolysis, or reduction:

• Oxidation: Involves combining particles with oxygen to form a larger particle structure.
• Hydrolysis: Water is used to break down compounds, resulting in new bond formations and larger particles.
• Reduction: Electrons are added to smaller particles to promote bonding into larger forms.

These processes help in forming stable colloids that do not dissolve readily in the medium, marking their characteristics as lyophobic.

Dispersion Method

In contrast to condensation, the dispersion method involves breaking down larger solid particles into colloid-sized pieces. This reduction is achieved by applying physical forces or external energy.

There are different techniques within the dispersion method:

• Mechanical Grinding: Involves using a grinder or mill to physically break down the particles, reducing their size drastically.
• Ultrasonication: Utilizes high-frequency sound waves to agitate the particles, causing them to break apart into much smaller sizes.
• Electrical Dispersion: Applies electric fields to disintegrate material into finer particles.

Each technique aims to create a balanced and evenly distributed colloidal system, where the resulting material is typically more resistant to settling and separating from the dispersion medium.

Colloidal Systems

Colloidal systems are mixtures where one substance of microscopically dispersed insoluble particles is suspended throughout another substance. This system can be identified by unique properties, such as the Tyndall effect, where light is scattered by the particles in the colloid.
There are two main types of colloidal systems depending on the interaction between the dispersed phase and the medium:

• Lyophilic colloids: The particles have an affinity for the solvent, leading to more stable and easily formed colloids.
• Lyophobic colloids: The particles lack affinity for the solvent, typically requiring special preparation methods, like the previously mentioned condensation and dispersion methods.

Understanding these systems is crucial because colloids are found in many natural processes and applications, including food production, pharmaceuticals, and environmental sciences.