Problem 36 - A Complete Resource Book in Chemistry for JEE Main

Question

A colloidal solution of a liquid, in a solid is termed as (a) aerosol (b) gel (c) emulsion (d) sol

Step-by-Step Solution

Answer

(b) gel

Step 1: Understand colloidal solutions

Colloidal solutions consist of small particles dispersed in another substance without settling. These are intermediary states between true solutions and suspensions. The dispersed phase can be a solid, liquid, or gas.

Step 2: Define the terms in the context

An aerosol is a colloidal solution of a liquid in gas. A gel is a colloidal solution where a liquid is dispersed in a solid, forming a jelly-like mass. An emulsion is a mixture of two liquids that are typically immiscible. A sol is a colloid where solid particles are dispersed in a liquid.

Step 3: Match the definitions to the options

We need a colloidal solution of a liquid in a solid. Comparing this with the definitions, 'gel' fits as it describes a jelly-like mass where the liquid is dispersed in a solid.

Key Concepts

Aerosol

An aerosol is a type of colloidal solution where fine liquid droplets or solid particles are dispersed in a gas. This creates a stable mixture that is often used in everyday products like sprays.

• An example of a natural aerosol is the mist from the sea, where tiny water droplets are suspended in the air.
• In manufactured products, aerosols can be found in items like deodorant sprays and paint sprays.

The particles in an aerosol are usually so small that they remain suspended for a long time without settling down, making the mixture appear homogeneous. However, unlike true solutions, these particles can often scatter light due to their size, a phenomenon known as the Tyndall effect.

Gel

A gel is formed when a liquid disperses within a solid, resulting in a colloid with a jelly-like consistency. This kind of colloidal system is stable and doesn't easily separate into its constituent parts.

• Common examples of gels include jelly desserts and various skincare products.
• In nature, gels can be seen in biological tissues and plant cell walls.

The stability of a gel depends on the nature of the solid matrix, which traps the liquid within its structure. This setup provides both elasticity and firmness, allowing gels to hold their shape yet remain moist.

Emulsion

An emulsion is a colloid consisting of two immiscible liquids, where one liquid is dispersed within another. This mixture is often stabilized with the help of emulsifying agents, which prevent the liquids from separating.

• Mayonnaise is a well-known example, where oil droplets are dispersed in vinegar or lemon juice, stabilized by egg yolk as an emulsifier.
• Milk is another natural example, with fat droplets dispersed in water.

Emulsions can be either oil-in-water or water-in-oil, depending on which liquid forms the continuous phase. These systems require thorough mixing and the right balance of ingredients to remain stable and uniform.

Sol

A sol is a type of colloid where solid particles are evenly distributed in a liquid. This mixture maintains stability as the solid particles are tiny and do not settle over time.

• Paint is a practical example of a sol, with pigments dispersed to form a uniform mixture.
• Another example includes blood, where cells are suspended in plasma.

Sols are characterized by their ability to flow due to the interaction between the liquid and the dispersed solid. The solid particles often provide color or special reflective properties which can be advantageous in applications like inks and dyes.