Problem 13 - A Complete Resource Book in Chemistry for JEE Main

Question

In the adsorption of oxalic acid on activated charcoal, the activated charcoal is known as (a) adsorber (b) adsorbent (c) absorber (d) adsorbate

Step-by-Step Solution

Answer

Activated charcoal acts as an adsorbent.

Step 1: Define Key Terms

First, let's clarify the terms involved in adsorption. **Adsorption** is a process where molecules stick to the surface of a solid. The solid on which the molecules adhere is called the **adsorbent**, while the molecules being adhered to the surface are referred to as the **adsorbate**.

Step 2: Identify the Role of Activated Charcoal

In this problem, activated charcoal is involved in the adsorption process. The problem asks to determine what role the activated charcoal plays in this context. Since activated charcoal is the surface onto which oxalic acid molecules adhere, it plays the role of the adsorbent.

Step 3: Select the Correct Term

Given the definitions: the **adsorbent** is the substance that provides the surface for adsorption. In this exercise, activated charcoal is where oxalic acid molecules are adsorbed. Therefore, the correct choice based on these definitions is (b) **adsorbent**.

Key Concepts

Adsorbent

An adsorbent is a material that provides a surface for the process of adsorption. This is crucial in various applications like purification and filtration. The key characteristic of an adsorbent is its surface area. A larger surface area provides more space for molecules to stick to.

Adsorbents are often solids, and they must be inert or non-reactive with the molecules they attract. They can be zeolites, silica gels, or clays, but the choice depends on the application requirements. They must effectively capture and hold onto the molecules of the adsorbate.

Common qualities of an effective adsorbent include:

• High surface area
• Porous structure
• Thermally stable
• Resistant to chemical reactions

An example of an adsorbent is activated charcoal, which is often used due to its highly porous nature, making it excellent for capturing small molecules.

Adsorbate

The adsorbate is the substance that is being collected on the surface of the adsorbent during adsorption. It is typically composed of molecules or atoms that accumulate on the solid surface.

This process involves weak van der Waals forces, electrostatic attraction, or even chemical bonding. The efficiency of adsorption depends on the nature of interaction between adsorbate and adsorbent.

Attributes of an efficient adsorbate include:

• Appropriate size to fit into pores of the adsorbent
• High affinity for the adsorbent surface
• Low vapor pressure at adsorption temperature

In our case study, oxalic acid serves as the adsorbate, which is collected on the surface of activated charcoal. The delicate interplay between oxalic acid and the surface of the charcoal facilitates the adsorption process.

Activated Charcoal

Activated charcoal is a highly porous form of carbon that offers a substantial surface area for adsorption processes. This makes it an exemplary adsorbent. It is used to purify, decolorize, and deodorize due to its excellent adsorptive properties.

Activation increases its surface area and pore size. This is achieved through physical or chemical processes, which remove molecular obstructions. The result is a vast, accessible area for molecules to adhere.

Key features of activated charcoal include:

• Huge surface area compared to its volume
• High porosity
• Low cost and easy availability
• Ability to remove a wide range of pollutants

In the context of adsorption, activated charcoal serves as the adsorbent, providing a surface for molecules like oxalic acid to adhere to, effectively removing it from solutions or gases.