Problem 180 - A Complete Resource Book in Chemistry for JEE Main

Question

Assertion: Detergents with low CMC are more economical to use Reason: Cleansing action of detergents involves the formation of micelles. These are formed when the concentration of detergents becomes equal to CMC.

Step-by-Step Solution

Answer

Both the assertion and the reason are true, and the reason correctly explains the assertion.

Step 1: Understanding the Assertion

The assertion states that detergents with low Critical Micelle Concentration (CMC) are more economical. CMC is the concentration at which micelles form, determining the minimum detergent required to start effective cleaning.

Step 2: Understanding the Reason

The reason provided explains that micelles are essential for the cleansing action of detergents and form when the detergent concentration reaches the CMC. Lowering CMC means less detergent is required to achieve this micelle formation.

Step 3: Assessing the Link between Assertion and Reason

The assertion claims economic benefit due to lower CMC detergents needing less product to start forming micelles and performing cleansing. The reason describes the necessity of reaching CMC to initiate cleansing, fitting logically with the assertion.

Step 4: Evaluating the Assertion and Reason

Since both the assertion and the reason correctly describe the relationship between CMC and detergent efficiency, and the reason accurately justifies the assertion, both statements are true and the reason is the correct explanation of the assertion.

Key Concepts

Cleansing action of detergents

The cleansing action of detergents is an essential process that helps in removing dirt and grease from surfaces. This is primarily due to the detergent's ability to form micelles. When you apply detergent to a dirty surface, it interacts with both water and oil molecules. The detergent molecules have a unique structure that allows them to bind with these unlike substances.

Detergents have two types of ends: a hydrophilic head that likes water and a hydrophobic tail that repels water but attaches to grease.

• The hydrophobic tail buries into the grease or dirt.
• The hydrophilic head stays in the water, pulling the grease into solution and away from the surface.

This allows the dirt to be washed away. When a detergent reaches a certain concentration, known as the Critical Micelle Concentration (CMC), micelles form, which further enhance this cleansing action.
The formation of micelles encapsulates the oily dirt inside them, making it possible to rinse it away with water. Without reaching this CMC, the detergent cannot perform effectively.

Micelle formation

Micelle formation is a chemical phenomenon that plays a pivotal role in the cleaning power of detergents. A micelle is a cluster of detergent molecules that organize in a spherical shape when they reach a specific concentration in water.

These micelles are clever little structures:

• Their core is non-polar and attracts oils and fats, effectively trapping dirt within.
• The outer surface is polar, interacting strongly with water, allowing the whole micelle to be rinsed away.

To reach the micelle formation concentration, known as the Critical Micelle Concentration (CMC), is essential for detergents to effectively mix with fats and oils.
Before reaching the CMC, detergent molecules simply float around in water without forming these crucial clusters.
When the concentration of the detergent surpasses the CMC, micelles spring into action, and the detergent can efficiently clean dirt and oils through this emulsification process.

Detergent efficiency

Detergent efficiency is crucial for cost-effective and environmentally friendly cleaning routines. Lowering the Critical Micelle Concentration (CMC) enhances this efficiency. Detergents with lower CMC need less product to form the micelles necessary for effective cleansing action.

This means several advantages:

• Less detergent is needed to achieve optimal cleaning, making it more economical.
• Reduced chemical waste, which is beneficial for the environment.

More efficient detergents lead to reduced water usage as they clean more effectively with less product. Such detergents also ensure that fabrics and materials are not subject to excessive chemical exposure.
Choosing a detergent with a low CMC is a wise decision for both personal cost savings and environmental conservation efforts. These factors explain why noting the CMC in detergents is important for both daily household cleaning and industrial applications.