Problem 144 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following process is not responsible for the presence of electric charge on the sol particles? (a) Adsorption of ionic species from solution (b) Electron capture by sol particles (c) Absorption of ionic species from solution (d) Formation of Helmholtz electrical doable layer.

Step-by-Step Solution

Answer

(c) Absorption of ionic species from solution is not responsible for electric charge on sol particles.

Step 1: Understanding Sol Particles and Charge

Sol particles are colloidal particles that can acquire an electric charge in various ways, influencing their stability and interactions.

Step 2: Evaluating Adsorption of Ionic Species

Adsorption of ions from the solution to the surface of sol particles can impart charge, contributing to the stability of the colloidal system. This process helps particles repel each other and stay dispersed.

Step 3: Considering Electron Capture

Sol particles can capture free electrons from their environment, gaining a net charge. This electron capture contributes to their overall electric charge.

Step 4: Checking Absorption versus Adsorption

Absorption implies that ions are taken into the bulk of the sol particles, rather than just adhering to their surface, which does not typically contribute to a net surface charge on sol particles.

Step 5: Formation of Helmholtz Electrical Double Layer

The formation of a Helmholtz electrical double layer involves the distribution of ions around charged particles, stabilizing them in solution, but the charge itself is usually established prior to the double-layer formation. This process sustains existing charge rather than creating it.

Step 6: Conclusion and Identification of the Odd Process

Among the processes listed, absorption (not to be confused with adsorption) of ionic species doesn't contribute to a net electric charge on the surface of sol particles. Hence, it is the process not responsible for the presence of electric charge.

Key Concepts

Adsorption

Adsorption is a key process in colloidal stability. It involves the accumulation of ions or molecules on the surface of sol particles. Unlike absorption, where substances penetrate into the bulk of material, adsorption occurs only at the surface.
This surface phenomenon provides sol particles with a charge by adhering ions to their surface. This charge is crucial for maintaining stability in colloidal systems, as it creates repulsive forces that prevent particles from clumping together.

• Adsorption contributes to electric charge on sol particles' surfaces.
• It enhances colloidal stability by promoting particle repulsion.
• It is a surface-level interaction distinct from absorption.

Understanding adsorption is essential for clarity on how charges form on colloidal particles and keep them apart and suspended in a solution.

Electron Capture

Electron capture is another process by which sol particles can obtain an electric charge. In this context, sol particles absorb free electrons available in their environment.
This acquisition of electrons results in a negative charge for the sol particles. It plays a substantial role in influencing their stability and behavior within the colloidal solution.

• Electron capture bestows a negative charge on sol particles.
• This process affects the overall charge balance of the colloidal system.
• It works alongside adsorption to stabilize particles in solution.

With electron capture, students can understand one of the fundamental ways sol particles gain charge, differentiating it from ion adsorption and other mechanisms.

Helmholtz Electrical Double Layer

The Helmholtz electrical double layer is a structured layer of ions that forms around a charged particle in a solution. This layer consists of two distinct parts: the Stern layer (close to the particle) and the diffuse layer (further away).
The Stern layer is made up of ions tightly bound to the charged particle's surface, neutralizing part of the surface charge. On the other hand, the diffuse layer contains ions that are less tightly bound and spread out into the solution, further balancing the charge.

• The Helmholtz layer stabilizes charged colloidal particles in a solution.
• It ensures that charged particles remain separated, thus preventing aggregation.
• This layer sustains the existing electric charge rather than creating a new one.

This concept helps students appreciate how the Helmholtz electrical double layer supports the stability of already charged sol particles, preventing them from aggregating and settling out of the solution.