Question

Fog is an example of colloidal system of: (a) liquid in a gas (b) gas in a liquid (c) gas in a solid (d) solid in a liquid

Short answer

Fog is an example of a colloidal system of liquid in a gas (a).

Step-by-step solution

Identify the Phases in Fog

Fog consists of tiny water droplets suspended in the air. The water droplets represent the dispersed phase, while air acts as the continuous phase.

Determine the State of Matter for Each Phase

The water droplets are in the liquid state, and the air is in the gaseous state.

Match the States of Matter to the Types of Colloidal Systems

By matching the states of matter of the dispersed phase and the continuous phase to the types of colloidal systems, we find that liquid in a gas corresponds to a system where liquid (dispersed phase) is mixed within a gas (continuous phase).

Key concepts

Liquid in a Gas

When we explore the concept of a 'liquid in a gas', we refer to a specific type of colloidal system. In the context of our exercise, fog serves as a prime example of this colloidal system. As you might have seen, fog appears as a sort of mist, composed of countless tiny droplets of water suspended in the air. But what makes it a colloidal system instead of just a mixture? The answer lies in the size of these water droplets and how they interact with light.

One of the unique properties of colloidal systems is the Tyndall effect, which is displayed when light scatters as it passes through the system, illuminating the path of the light beam. Next time you notice beams of sunlight filtering through fog, you're actually witnessing this effect in action. Moreover, these systems are quite stable due to the tiny size of the dispersed droplets, which don't settle under the influence of gravity. They remain suspended in the air, creating that eerie effect that can turn a clear day into a pea souper.

Dispersed Phase

The dispersed phase in colloidal systems refers to the particles that are disseminated throughout another substance. In our case with fog, the dispersed phase consists of the liquid water droplets. The size of these droplets is crucial; they are small enough to remain airborne, yet large enough to be distinct from the molecules of the dispersing medium, which in this case, is air. This intermediate size is the hallmark of colloidal particles.

Understanding the dispersed phase helps explain why colloids exhibit both particle and wave nature, similar to how the concept of duality is present in quantum mechanics. In colloids, the dispersed phase particles are sufficiently large to scatter light, yet they behave as part of a fluid medium on a macroscopic scale. The stability of the dispersed phase is often enhanced by repulsive forces, such as electrical charges that keep the particles from aggregating.

Continuous Phase

Contrasting with the dispersed phase, the continuous phase is the medium in which the colloidal particles are distributed. In the example of fog, the continuous phase is the air. The air's role is pivotal as it allows the liquid droplets to remain dispersed evenly throughout it. The continuous phase is not just a passive space-filler; it interacts with the dispersed phase in ways that define the properties of the colloid.

To visualize this interaction, consider a colloid as a dance hall, where the dispersed particles are the dancers, and the continuous phase is the hall itself. Just as the size and shape of the dance hall can influence how the dancers move, the properties of the continuous phase, such as viscosity and temperature, can significantly affect the behavior of the dispersed particles. When it comes to fog, factors like air density and humidity can have a big impact on its formation and dissipation.