Problem 158 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following statements are correct? (a) Presence of equal and similar charges on colloidal particles provides stability to the colloids(b) Mixing two oppositely chartged sols neutralises their charges and stabilises the colloid. (c) Brownian movement stabilises sols (d) Any amount of dispersed liquid can be added to emulsion without destabilising it.

Step-by-Step Solution

Answer

Statements (a) and (c) are correct. (b) and (d) are incorrect.

Step 1: Understanding Stabilization of Colloids

Colloids are stable due to the repulsion between like charges on their surfaces. Particles in a colloid repel each other due to similar charges, preventing them from coming too close and thus stabilizing the colloid.

Step 2: Analyzing Mixing of Oppositely Charged Sols

When two sols with oppositely charged particles are mixed, their charges may neutralize each other. Neutralization reduces repulsion and can lead to coagulation, not stabilization. Therefore, mixing oppositely charged sols usually destabilizes the colloid.

Step 3: Evaluating the Role of Brownian Motion

Brownian motion refers to the random movement of particles in a fluid, caused by collisions with molecules of the dispersion medium. While Brownian motion helps keep the particles suspended, it does not directly stabilize the sol.

Step 4: Assessing Behavior of Emulsions

In emulsions, a specific quantity of dispersed liquid is held in place by an emulsifier. Adding too much dispersed liquid can exceed the emulsification capacity, leading to destabilization. Hence, adding any amount of dispersed liquid without consideration can indeed destabilize the emulsion.

Key Concepts

Electrostatic Stabilization

In colloidal systems, electrostatic stabilization is crucial for maintaining stability. Colloidal particles tend to possess similar charges on their surfaces. These identical charges create a repulsive electric force that prevents the particles from coming too close together.
This repulsion is essential in preventing aggregation of particles, which would otherwise lead to settling or agglomeration of the colloid.

• Each particle in a colloid carries a similar charge, creating a net repulsive effect.
• This repulsion helps maintain a stable, evenly dispersed colloidal suspension.
• Without sufficient charge repulsion, the particles could collide, aggregate, and form larger clusters.

Combining this mechanism with the colloid's environment allows the particles to remain in suspension without rapidly settling to the bottom, enhancing the overall stability of the colloidal solution.

Brownian Motion

Brownian motion plays a fascinating role in colloidal stability, although its effect is indirect. Characterized by the random, jittery movement of particles in a colloid, Brownian motion is caused by the collisions with the smaller molecules of the dispersion medium, often a fluid.
This movement contributes to keeping the particles dispersed and suspended in the medium.

• Particles are in constant random motion, preventing them from settling due to gravity.
• It enhances diffusion throughout the colloid, maintaining an even distribution of particles.
• However, Brownian motion alone does not provide sufficient stabilization for colloids.

This kinetic energy reduces the chances of particles settling down, but while it supports the suspension of particles, it does not directly stabilize them as effectively as charge repulsion does.

Emulsification

Emulsification involves the mixing of two immiscible liquids, such as oil and water, into a stable colloidal mixture or emulsion. This process is generally facilitated by an emulsifier, a substance that helps these two unlikely companions combine.
The principle behind emulsifying agents is their dual affinity; they contain both hydrocarbon tails (lipophilic) and polar heads (hydrophilic).

• Lipophilic tails bind to oil, while hydrophilic heads interact with water.
• This creates a bridge between the two phases, preventing separation.
• Too much dispersed liquid beyond the emulsifier's capacity can lead to phase separation or destabilization.

Through emulsification, a specific amount of liquid can be dispersed, while maintaining stability. However, excessively adding dispersed liquid without compensating with enough emulsifier could exceed the system's stabilization capacity, causing the emulsion to break down.