Problem 28 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

Choose the correct reason(s) for the stability of the lyophobic colloidal particles.(a) Preferential adsorption of ions on their surface from the solution. (b) Preferential adsorption of solvent on their surface from the solution. (c) Attraction between different particles having opposite charges on their surface. (d) Potential difference between the fixed layer and the diffused layer of opposite charges around the colloidal particles.

Step-by-Step Solution

Answer

Options (a) and (d) are correct.

Step 1: Understanding the Problem

Lyophobic colloids are those in which particles do not have an affinity for the dispersion medium. For such particles, the main factors contributing to their stability need to be identified. The options given provide different processes that could potentially stabilize these particles.

Step 2: Analyzing Option (a)

The option (a) refers to the preferential adsorption of ions on the particles' surface from the solution. This is a common practice in stabilizing colloidal particles, as the adsorbed ions create a charged layer around the particles, which prevents them from coming together due to repulsion between like charges.

Step 3: Analyzing Option (b)

The option (b) involves the preferential adsorption of the solvent on the surface of the particles. This process is more typically associated with the stabilization of lyophilic colloids than lyophobic ones, as lyophilic colloids have an affinity for the solvent.

Step 4: Analyzing Option (c)

Option (c) describes attraction between particles with opposite charges. However, for lyophobic colloids, particles generally have like charges due to adsorbed ions, which repel each other to prevent aggregation. Thus, this option does not explain the stability.

Step 5: Analyzing Option (d)

Option (d) talks about the potential difference between the fixed layer and the diffused layer of opposite charges, known as the electrical double layer. This potential difference, termed as zeta potential, is crucial in maintaining colloidal stability by preventing particles from coming together.

Step 6: Conclusion

The stability of lyophobic colloidal particles is mainly due to the preferential adsorption of ions leading to charge repulsion, as described in option (a), and the presence of the electrical double layer with the potential difference preventing particle aggregation, as described in option (d).

Key Concepts

Lyophobic Colloids

Lyophobic colloids, often termed as "liquid hating" colloids, are types of colloidal systems where the dispersed particles do not have a natural affinity for the liquid or dispersion medium. Instead, they tend to repel the liquid, making them inherently unstable. However, their stability is crucial for various applications in chemical and biological processes.

To achieve this stability, certain mechanisms come into play. Primarily, these colloids require stabilization either through the adsorption of ions on their surface or by creating a potential difference around them. This prevents the particles from clumping together, maintaining their dispersed state.

• Lyophobic colloids are usually not stable without external assistance.
• They often require stabilization through charged layers on their surface.

Understanding how these colloids function and how they are stabilized helps in various fields like pharmaceuticals, paints, and food industries.

Zeta Potential

Zeta potential is a scientific term used to describe the potential difference across the electrical double layer surrounding a colloidal particle. This concept is critical in understanding the stability of colloidal systems.

When ions adsorb onto the surface of lyophobic colloids, they create a charged layer. This layer does not only influence the surface potential, but it also helps in forming the electrical double layer, which is a structure made of a fixed layer and a diffused layer of ions.

The zeta potential is the difference in electric potential between the fixed layer closely attached to the colloidal particle and the dynamic, diffused layer.

• Zeta potential determines the overall stability of the colloid.
• A high zeta potential means strong repulsion between particles, ensuring stability.
• If the zeta potential is low, particles may come together and the colloid becomes unstable.

Therefore, controlling zeta potential is essential in managing the behavior of lyophobic colloids in solution.

Adsorption of Ions

The adsorption of ions onto the surface of colloidal particles is an essential process in stabilizing lyophobic colloids. This process involves ions from the solution attaching themselves preferentially to the surface of the colloidal particles.

By adsorbing ions, colloidal particles acquire like charges. The presence of these like charges introduces electrostatic repulsion among the particles, which prevents aggregation by causing them to repel each other.

Some key points regarding this phenomenon include:

• Adsorption helps create a strong ionic layer around the particles.
• A uniform charge distribution on particle surfaces aids in repelling other particles.
• It is significant for achieving colloidal stability in systems where particles do not naturally attract the solvent.

The adsorption of ions thus plays a crucial role in maintaining the dispersed, stable state of lyophobic colloids.

Electrical Double Layer

The electrical double layer is a fundamental concept that describes the structure formed around a colloidal particle in a solution, contributing greatly to colloidal stability. It consists of two layers of charge surrounding the particle.

The first layer, known as the fixed or stern layer, is where ions are tightly bound to the particle's surface. These ions influence the colloid's initial charge. The second layer, or the diffuse layer, consists of ions more loosely associated and spread out into the solution. These ions balance the charge of the fixed layer and extend into the surrounding fluid.

This dual-layer structure creates a potential difference, known as the zeta potential, crucial for preventing particle aggregation by maintaining repulsion between particles. Key aspects of the electrical double layer include:

• Ensuring a stable charge environment around particles.
• Creating a repulsion mechanism to prevent clumping of colloidal particles.
• Managing interactions between colloidal particles and the surrounding medium.

Understanding the electrical double layer is vital for effectively manipulating and stabilizing lyophobic colloids.