Problem 39 - A Complete Resource Book in Chemistry for JEE Main

Question

The separation of colloidal particles from those of molecular dimensions is called (a) dialysis (b) photolysis (c) peptization (d) pyrolysis

Step-by-Step Solution

Answer

The correct answer is (a) dialysis.

Step 1: Understand the Terms

First, let's clarify each term. Dialysis is a process by which particles are separated based on their size using a semipermeable membrane. Photolysis involves breaking down compounds by light. Peptization is the process of breaking down into smaller particles or solutions by adding an agent. Pyrolysis is the decomposition of materials at high temperatures.

Step 2: Connect the Definition

The question asks for the separation of colloidal particles from molecular dimensions. Colloidal particles are larger than molecules, so a method that separates based on size is needed. Dialysis matches this description, as it separates based on size using a membrane that allows smaller molecules to pass through while retaining larger particles.

Step 3: Compare Remaining Options

Evaluate the other options: Photolysis involves light, not size exclusion, so it is not relevant here. Peptization focuses on breaking down into smaller particles, which doesn't align with separating existing particles based on size. Pyrolysis involves heat and decomposition, not size-based separation. Thus, these options do not align with the given problem.

Step 4: Confirm the Correct Answer

Based on the comparison and definitions, dialysis is the only process that meets the requirement of separating particles based on size, specifically colloidal from molecular-sized particles.

Key Concepts

Dialysis

Dialysis is a fascinating process used to separate particles based on size. This technique utilizes a membrane that acts like a sieve. Larger particles, like colloids, are retained, while smaller ones, which are molecular in size, pass through the membrane. This method is commonly seen in medical treatments, like kidney dialysis, where waste products are filtered from the bloodstream. The key to dialysis is the semipermeable membrane, which selectively allows smaller molecules to diffuse while keeping larger ones contained. This size-based approach makes dialysis an essential technique in both medical and laboratory settings.

Size-based Separation

Size-based separation is an essential concept in chemistry and biology, allowing for the sorting of particles based solely on their physical dimensions. This method is key to processes such as dialysis, filtration, and even centrifugation. In daily applications, size-based separation can be seen in:

• Water purification, where filters trap contaminants larger than water molecules.
• Medical laboratories, where centrifuges separate cells and proteins by size.

It is a fundamental technique because many processes rely on the ability to sort and separate different types of particles accurately. Understanding this concept helps in designing systems that effectively filter or separate mixtures.

Colloidal Chemistry

Colloidal chemistry deals with substances that have particles ranging in size from 1 nanometer to 1 micrometer. These particles are larger than typical molecules but smaller than those visible to the naked eye. Colloids can be found in various forms, such as:

• Emulsions, where liquids mix without dissolving, like oil in water.
• Gels, which are semi-solid and have a fibrous structure.
• Sols, where solid particles are dispersed in a liquid.

Colloidal particles do not settle easily, giving many colloids their unique characteristics. In the natural and industrial world, colloidal chemistry is crucial in food production, paint manufacturing, and even pharmaceuticals.

Molecular Dimensions

Molecular dimensions refer to the size of individual molecules, which are typically measured in nanometers or angstroms. Understanding these dimensions is vital in chemistry for several reasons:

• It helps predict the behavior of molecules during reactions.
• Determines how molecules interact with light and other electromagnetic radiation.
• Aids in designing drugs that can target specific molecules in the body.

Molecular dimensions are important in distinguishing between molecular-sized entities and larger colloidal particles. This distinction is essential, especially in techniques like dialysis, where the goal is to separate particles based purely on size.