Difference Between Colloid and Suspension

Main Difference – Colloid vs Suspension

Colloids and suspensions are both considered as mixtures where the components are not chemically bonded to each other. The main difference between colloid and suspension lies in the size of particles. Colloid particles are much smaller than suspension particles. Due to this size difference, colloid particles can be either homogeneous or heterogeneous at given conditions, whereas suspensions are always heterogeneous.

This article explains, 

1. What are Colloids
     – Definition, Properties, Examples
2. What are Suspensions
     – Definition, Properties, Examples
3. How to Distinguish Colloids from Suspensions
4. What is the difference between Colloid and Suspension

What are Colloids

The size of colloid particles ranges from 1 nm to 200 nm. The colloidal particles which are dispersed in the dispersion medium are called dispersed phase. Colloid particles are prevented from settling down by Brownian motion. These systems are mostly translucent as light is scattered by particles. Colloids are not easily separated from the dispersion medium. Techniques such as centrifugation, dialysis, and ultrafiltration are required to separate colloids. Colloid particles can be molecules or molecular aggregates. In a colloidal system, phase separation can happen, but not readily. Two phases may separate by leaving to stand for a long time. Phase separation occurs in lyophobic colloidal systems where the dispersed phase does not have a great affinity for the dispersion medium. Lyophilic systems, in contrast, do not show phase separation as the dispersed phase is physically attracted to the dispersion medium. Colloid particles pass through filter papers.

Examples of Colloidal Systems 

Figure 1: Milk – Example of Liquid-Liquid Colloid

What are Suspensions

Suspension particles are much larger than colloid particles. Due to their size, they do not pass through filter papers and can be recovered by filtration. These particles are visible to the naked eye. Light do not travel through these large particles. Hence, the systems are often opaque.

Suspensions are heterogeneous. The suspension particles undergo sedimentation when the system is left to stand. This is due to the gravitational force on the particles and the absence of Brownian motion.

If you put a little bit of CaCO₃ into water and stir the system, first you will see a milky colour solution which seems to be homogeneous. But it does not remain the same. The particles tend to undergo sedimentation as soon as stirring is stopped. After some time, you can see a layer of CaCO₃ at the bottom of the container.

Examples of Suspensions

Solid in liquid:  Muddy water, CaCO₃ in water

Liquid in liquid: Oil in water (liquid-liquid systems are called emulsions)

Solid in Liquid:  Soot particles in air

How to Distinguish Colloids from Suspensions

Several methods can be adopted to distinguish colloids from suspensions.

When filtered through filter paper colloids will pass through the paper whereas suspended particles will be retained on.

When the system is left to stand some time, suspended particles will readily undergo sedimentation whereas colloidal particles remain in the solution.

Brownian motion is also another factor that can be used to distinguish the difference between colloid and suspension. It is the random movement and collision between the molecules. Colloidal particles undergo Brownian motion since they are small enough for random movement and collisions. Therefore, they don’t settle easily and separate out. Large suspended particles don’t undergo Brownian motion and they easily settle.

Figure 2: Oil in Water – Example of a Suspension

Difference Between Colloid and Suspension

Size of Particles

Colloid: Colloid particles are comparatively small (1-200 nm).

Suspension: Suspension particles are comparatively large (> 200 nm).

Permeability through Filter Paper

Colloid: Particles pass through filter paper. 

Suspension: Particles don’t pass through filter paper. 

Particle Visibility

Colloid: Particles cannot be seen by the naked eye but can be seen under a light microscope.

Suspension: Particles can be clearly seen by naked eye.

Sedimentation

Colloid: Particles do not undergo sedimentation.

Suspension: Particles undergo sedimentation. 

Phase Separation

Colloid: Phase separation is either very slow or might not happen. 

Suspension: A distinct phase separation can be seen. 

Applications

Colloid: Colloids are used in the paint industry, food industry, perfume industry and various other industrial application.

Suspension: Suspensions are used in the production of medication and milk of magnesia.

Examples

Colloid: Milk, shampoo, gemstones, and foam rubber are examples of colloids.

Suspension: Muddy water, soot in air, oil and water are examples of suspensions

Summary – Colloid vs Suspension

Suspended particles are the largest category of particles in mixtures. Colloids are of medium size, and solution molecules are the smallest. The various differences mentioned in the table above are all caused by the difference in the size of particles, which is also the main difference between colloid and suspension.

Reference:

“Solutions, Suspensions, Colloids — Summary Table.” EdInformatics.Com. N.p., n.d. Web. 06 Feb. 2017.

Verma, N. K., B. K. Vermani, and Neema Verma. “Surface Chemistry.” Comprehensive Practical Chemistry Class-XII. N.p.: Laxmi Publications, 2008. N. pag. Print.

Image Courtesy:

“Water and oil” By Victor Blacus – (GFDL) via Commons Wikimedia 

“925858” (Public Domain) via Pixabay