Question

What type of colloid is each of the following? (a) Milk (b) Fog \(g\) (c) Shaving cream

Short answer

Milk - Emulsion, Fog - Aerosol, Shaving cream - Foam

Step-by-step solution

Understand the definition

A colloid is a type of heterogeneous mixture where one substance is dispersed in another. Colloids are classified based on the phase (solid, liquid, gas) of the dispersed substance and the continuous medium.

Classify Milk

Milk is an emulsion. An emulsion is a colloid where both the dispersed phase and the continuous medium are liquids. In milk, the fat droplets are dispersed in water.

Classify Fog

Fog is an example of an aerosol. An aerosol is a colloid where solid or liquid particles are dispersed in a gas. In fog, tiny water droplets are dispersed in air.

Classify Shaving Cream

Shaving cream is a foam. A foam is a colloid where a gas is dispersed in a liquid. In shaving cream, air is dispersed in a liquid/cream.

Key concepts

Emulsion

An emulsion is a type of colloid where both the dispersed phase and the continuous medium are liquids. One common example of an emulsion is milk. In milk, tiny fat droplets are dispersed uniformly throughout water, creating a stable mixture. Emulsions can be found not just in foods but in many cosmetic and pharmaceutical products as well.

• Think of salad dressings that have oil and vinegar mixed together.
• Mayonnaise is another example where oil is dispersed within the continuous phase of egg yolk and vinegar or lemon juice.
• Even lotions and creams you use are emulsions!

For an emulsion to remain stable, emulsifying agents are often added to prevent the liquids from separating.

Aerosol

Aerosols are colloids where fine solid particles or liquid droplets are dispersed in a gas. An excellent example of an aerosol is fog. In fog, tiny water droplets are dispersed throughout the air. Aerosols can be naturally occurring or man-made and can take many forms.

• Clouds are natural aerosols made up of water droplets in the air.
• Hairspray is a man-made aerosol where liquid particles are dispersed in gas.
• Pollens, dust, and even smoke are examples of solid particles dispersed in air.

In general, aerosols play a significant role in weather patterns and in the dispersal of various substances in the environment.

Foam

Foam is a type of colloid where a gas is dispersed in a liquid. Shaving cream is a familiar example of foam. In shaving cream, tiny air bubbles are dispersed within the liquid or cream, giving it a light and frothy texture. Another commonly found foam is the froth on the top of a cappuccino, where air is trapped in the liquid coffee.

• Soaps and detergents can create foam when mixed with water due to trapped air bubbles.
• Certain building materials like foam insulation are used for their lightweight and insulating properties.
• Sea foam, which you may have seen on the ocean shore, is also a natural example of foam.

Understanding foam is crucial for many industries, including food, cosmetics, and construction.

Heterogeneous Mixture

A heterogeneous mixture consists of two or more substances that are not uniformly distributed, meaning you can often see the different components. Colloids, including emulsions, aerosols, and foams, fall under the category of heterogeneous mixtures because their components remain distinct at the microscopic level.

• Salad is a classic example where you can see and separate each ingredient like lettuce, tomatoes, and cucumbers.
• Muddy water, where soil particles are suspended in water, is another example.
• Adds versatility to modern products like paints and medications.

Heterogeneous mixtures are found everywhere in nature and daily life, from the air we breathe to the food we eat.