Problem 83 - A Complete Resource Book in Chemistry for JEE Main

Question

Adsorption is a phenomenon, in which a substance (a) goes into the body of some other substance (b) accumulates on the surface of some other substance (c) remains close to some other substance (d) does not accumulate on the surface of some other substance

Step-by-Step Solution

Answer

(b) Accumulates on the surface of some other substance.

Step 1: Understanding Adsorption

Adsorption is a surface phenomenon where molecules or particles accumulate on the surface of a solid or a liquid. It describes how atoms, ions, or molecules from a gas, liquid, or dissolved solid adhere to a surface.

Step 2: Analyzing the Options

Evaluate each option in relation to the concept of adsorption: (a) refers to absorption, the penetration of a substance into another, not adsorption. (b) correctly refers to the accumulation on the surface, matching the definition of adsorption. (c) suggests proximity but not necessarily adherence to a surface, and (d) explicitly says no accumulation on the surface, which is contrary to the definition of adsorption.

Step 3: Choosing the Correct Option

Based on the understanding of adsorption and the analysis of the options, (b) is the correct choice as it defines adsorption as the accumulation of particles on the surface of another substance.

Key Concepts

Surface Phenomenon

Adsorption is an excellent example of a surface phenomenon. In simple terms, a surface phenomenon occurs when certain actions or behaviors take place predominantly on the outer layer or boundary of a material or object. In the context of adsorption, this means that the particles, like atoms, ions, or molecules, do not penetrate into the bulk of the adsorbent material. Instead, they gather on the surface.
Understanding surface phenomena helps us in fields ranging from material science to catalysis and even environmental science. For instance:

• Adsorption plays a crucial role in filters, where contaminants in water adhere to the surface of carbon particles.
• In catalysis, reactions often require substrates to adhere to the surface of the catalyst, which is possible through adsorption.

Recognizing adsorption as a surface phenomenon is key to differentiating it from other processes that might involve the bulk of the material rather than just the surface.

Difference Between Adsorption and Absorption

Adsorption and absorption might sound similar, but they are distinct processes. Adsorption, as we know, involves the gathering of particles on the surface of a material. On the other hand, absorption includes the penetration and distribution of a substance throughout the entire volume of another material.
Let's break this down with a couple of examples:

• Adsorption: When a sponge is used to soak ink, the ink molecules initially gather on the outer surface of the sponge fibers. This initial accumulation is adsorption.
• Absorption: Over time, the ink penetrates into the inner structure of the sponge and spreads out evenly. This movement inward is absorption.

The distinction is fundamental in many applications. For instance, in cleaning up spills or purifying chemicals, understanding whether a material adsorbs or absorbs substances dictates how it can be used effectively.

Molecular Adhesion

Molecular adhesion refers to the force that causes molecules to stick to a surface or to each other. In the process of adsorption, this adhesion is what keeps the adsorbed particles connected to the surface of the adsorbent material.
The forces involved in adhesion can vary, including:

• Van der Waals forces: These are weak intermolecular forces that play a significant role in molecular adhesion in adsorption.
• Hydrogen bonding: In some cases, such as water molecules on a surface, hydrogen bonds can enhance adhesion.

Understanding molecular adhesion is important as it dictates the effectiveness and strength of the adsorption process. Better adhesion means stronger and more effective adsorption, which is critical in processes such as air and water purification. Thus, molecular adhesion is a central concept when studying how substances adhere to surfaces in various scientific and industrial applications.