How do suspensions differ from colloids?

Short Answer

Suspensions differ from colloids mainly in particle size, settling behaviour, and appearance. In a suspension, the particles are large, visible, and settle down when left undisturbed. Examples include muddy water and flour in water. In contrast, colloids have much smaller particles that remain evenly spread and do not settle. Milk and fog are examples of colloids.

Suspensions are easily separated by filtration, while colloids cannot be separated this way. Suspensions appear cloudy and unstable, whereas colloids often look uniform and show the Tyndall effect by scattering light. These differences help us identify and classify mixtures.

Detailed Explanation

How suspensions differ from colloids

Suspensions and colloids are two important types of heterogeneous mixtures, but they differ in many ways because of the size and behaviour of their particles. Understanding the differences between them helps us recognise how mixtures behave in daily life, nature, laboratories, and industries. Even though both contain particles dispersed in a medium, their properties are not the same. The differences in stability, visibility, settling, and separation methods make them useful for different purposes.

At first glance, both suspensions and colloids may look cloudy or non-uniform, but their microscopic properties are quite different. Suspensions contain large particles that can be seen directly or with simple tools, while colloids contain particles so small that they cannot be seen even with a normal microscope. The interaction of these particles with the medium determines how each mixture behaves.

Difference in particle size

The most important difference between suspensions and colloids is particle size.

Suspensions

  • Contain large particles (greater than 1000 nm).
  • Particles are big enough to be seen and separated.

Colloids

  • Contain intermediate-sized particles (1–1000 nm).
  • Particles are too small to be seen with the naked eye.

This size difference influences all other properties of the mixtures.

Difference in settling behaviour

The way particles behave over time also separates suspensions from colloids.

Suspensions

  • Particles settle when the mixture is left undisturbed.
  • The settling occurs due to gravity because the particles are heavy and large.
  • The mixture needs to be shaken or stirred before use.

Example: Soil settles at the bottom of muddy water.

Colloids

  • Particles never settle naturally.
  • Brownian motion (random movement of particles) keeps them spread.
  • They remain stable for long periods.

Example: Milk remains mixed and does not separate into layers by itself.

Difference in appearance

Suspensions

  • Appear cloudy or opaque.
  • Particles scatter light strongly or may block it.

Colloids

  • Appear uniform and clear, though sometimes slightly cloudy.
  • Show the Tyndall effect, where a beam of light becomes visible inside the mixture.

Example: Headlights visible through fog (a colloid).

Difference in filtration

Filtration is a simple method to separate mixtures, and it works differently for suspensions and colloids.

Suspensions

  • Can be easily separated by filtration.
  • Large particles get trapped on filter paper.

Colloids

  • Cannot be filtered using normal filter paper.
  • Very fine particles pass through easily.

Special techniques like ultrafiltration are needed for colloids.

Difference in stability

Stability describes how long a mixture remains unchanged.

Suspensions

  • Unstable mixtures.
  • Particles settle quickly because there is nothing to keep them suspended.

Colloids

  • Stable mixtures.
  • Particles remain dispersed due to their charge and random motion.

Difference in visibility of particles

Suspensions

  • Particles can be seen with the naked eye or simple magnification.

Colloids

  • Particles cannot be seen individually.
  • Only their effect, such as scattering of light, can be observed.

Examples

Common suspensions

  • Muddy water
  • Flour in water
  • Chalk powder in water
  • Some medicines like antacid mixtures

Common colloids

  • Milk
  • Fog
  • Jelly
  • Shaving cream
  • Blood

These examples show how differently mixtures can behave depending on particle size.

Importance of knowing the difference

Understanding how suspensions differ from colloids is useful in everyday life, science, and industries.

  1. Medicines

Some drugs are suspensions that must be shaken before use, while others are colloids that remain stable.

  1. Food and cooking

Soups and juices with pulp are suspensions, whereas milk, creams, and sauces are colloids.

  1. Environment

Dust in air forms a suspension, while fog and mist are colloids.

  1. Industries

Paints can be suspensions or colloids, and their handling depends on their type.

These differences guide how mixtures are stored, used, and separated.

Conclusion

Suspensions and colloids differ mainly in particle size, stability, visibility, settling, and separation methods. Suspensions have large particles that settle and can be filtered, while colloids have smaller particles that do not settle and cannot be filtered easily. Colloids also show the Tyndall effect, unlike suspensions. Knowing these differences helps us classify mixtures and understand how they behave in daily life and industry.