Problem 8 - A Complete Resource Book in Chemistry for JEE Main

Question

Milk is a colloid in which (a) liquid is dispersed in liquid (b) gas is dispersed in liquid (c) sugar is dispersed in water (d) solid is dispersed in liquid

Step-by-Step Solution

Answer

The correct answer is (a) liquid is dispersed in liquid.

Step 1: Understanding colloids in general

A colloid is a mixture where one substance of microscopically dispersed insoluble particles is suspended throughout another substance. These particles are between 1 nanometer and 1 micrometer in size.

Step 2: Identifying the specific type of dispersion

Milk contains fats, proteins, and other molecules uniformly dispersed in water. The primary component that makes milk a colloid is the fat droplets dispersed in the liquid water base.

Step 3: Matching the definition with options provided

In the context of the given options, we need to consider the dispersion of liquids in liquids to find the correct type of colloidal system. Milk is best characterized by a liquid-in-liquid dispersion—specifically, tiny fat droplets (a liquid) dispersed in water (also a liquid).

Step 4: Confirming the correct option

Upon evaluating, option (a) 'liquid is dispersed in liquid' correctly represents the colloidal nature of milk. In milk, liquid fat droplets are dispersed throughout the liquid water phase.

Key Concepts

Liquid Dispersion

Milk is a great example of liquid dispersion, a concept that explains how one liquid spreads throughout another without dissolving entirely. In this case, milk is composed of small fat droplets that are evenly distributed throughout the water. The key aspect of a liquid dispersion is the uniform distribution of one liquid within another. The fat droplets in milk, although microscopic, do not settle or separate, maintaining a stable mix. This process is important because it keeps milk smooth and consistent.

• Milk as an example: Fat droplets dispersed in water.
• Stable mixture: Fat droplets remain suspended without settling.

This aspect of milk defines its creamy texture and prevents it from separating, demonstrating the fascinating behavior of liquid dispersions in colloidal systems.

Microscopically Dispersed Particles

Microscopically dispersed particles are at the heart of colloidal systems like milk. These particles, between 1 nanometer and 1 micrometer in size, are so small that they remain suspended and do not easily separate out. In milk, the fat droplets serve as the microscopically dispersed component. These tiny particles are why milk does not appear as a simple liquid, but rather as a uniform yet complex suspension.

• Particle size: Between 1 nanometer and 1 micrometer.
• Stability: Particles remain suspended without settling.

This stability results from a balance of forces at this small scale, preventing the particles from merging or sinking. This makes milk a robust and homogeneous colloidal mixture.

Fat Droplets in Water

In the specific case of milk, fat droplets are dispersed phase, while water is the continuous phase. The fat in milk comprises tiny droplets that float within the water to create a creamy texture. This dispersion gives milk its appealing mouthfeel and physical properties.
Fat droplets in water implement one of the defining properties of colloids, where two immiscible substances coexist in a stable mix. The droplets are microscopic and do not dissolve, adding to milk's nutritional value and texture.

• Type of dispersion: Fat (droplets) in water (liquid).
• Texture and stability: Maintained by the uniform distribution of droplets.

Understanding this aspect not only explains the makeup of milk but also how such mixtures retain their properties over time. It allows them to be everyday food staples with distinctive tastes and qualities.