Difference Between Suspension and Colloid

The key difference between suspension and colloid is that the particles in a suspension are larger than the particles in a colloid.

A mixture is an association of several substances. Suspensions, solutions, and colloids are two examples of such mixtures. Since the components in a mixture do not chemically bind together, we can physically separate them by filtration, precipitation, evaporation, etc. There are mainly two types of mixtures, homogeneous mixtures and heterogeneous mixtures. In a homogeneous mixture, the composition is uniform, but in heterogeneous mixtures, it is not uniform.

1. Overview and Key Difference
2. What is Suspension
3. What is Colloid
4. Side by Side Comparison – Suspension vs Colloid in Tabular Form
5. Summary

What is Suspension?

Suspension is a heterogeneous mixture of substances (E.g., muddy water, flour dissolved in water). There are two components in a suspension, the dispersed material and the dispersion medium. There are larger solid particles (dispersed material) that distribute in a dispersion medium. The medium can occur as a liquid, gas or a solid. However, the dispersed material is usually solid.

Difference Between Suspension and Colloid

Figure 01: Settling down of Particles in Suspensions due to the effect of Gravity

However, if we allow the suspension to stand still for some time, the particles settle down to the bottom. If we mix it, the suspension forms again. The particles in a suspension are visible to the naked eye, and through filtration, we can separate them. Because of the larger particles, the suspensions tend to be opaque and not transparent, because they do not transmit light.

What is Colloid?

Colloidal solution appears as a homogeneous mixture, but it also can exist as a heterogeneous mixture (e.g., milk, fog). The particles in colloidal solutions are of intermediate size (larger than molecules) if we compare it with particles in solutions and suspensions, but as the particles in solutions, they are invisible to the naked eye, and we cannot filter them using a filter paper. We name the particles in a colloid as dispersed material, and the dispersing medium is analogous to the solvent in a solution.

Key Difference Between Suspension and Colloid

Figure 02: Milk is a Colloid

According to the dispersed material and the medium, there are different types of colloids. For instance, if the dispersed material is a gas in a liquid medium, the resulted colloid is ‘foam’ (e.g., whipped cream). If a colloid form from the combination of two liquids, we call it an emulsion (e.g., milk). The particles distribute within the colloidal medium and do not settle down if it is left still. Colloidal solutions are translucent or opaque. Sometimes, particles in a colloid separate out by centrifugation or coagulation. For example, the proteins in milk coagulate when we supply heat or if we add an acid.

What is the Difference Between Suspension and Colloid?

Suspensions and colloids are two types of mixtures that contain two or more substances mixed with each other. The key difference between suspension and colloid is that the particles in a suspension are larger than the particles in a colloid. Another major difference between suspension and colloid is that suspension is a heterogeneous mixture whereas colloid can exist as either a homogeneous or heterogeneous mixture. When considering the settling down of the particles in each mixture, particles in a suspension can settle down under the influence of gravity, if we do not disturb the settling process. But, the particles in a colloid do not settle down under normal conditions. Hence, this is also a difference between suspension and colloid.

However, due to the difference in particle sizes, particles of a suspension cannot pass through a filter paper, but the particles of a colloid can. If we consider the optical properties, we can find another difference between suspension and colloid. That is, the suspensions are opaque because they do not transmit light whereas the colloids are opaque or translucent because they can scatter light.

Summary – Suspension vs Colloid

Although both suspensions and colloids are mixtures of substances, there are several differences between them. The key difference between suspension and colloid is that the particles in a suspension are larger than the particles in a colloid.

Reference:

1. “Suspension (Chemistry).” Wikipedia, Wikimedia Foundation, 27 Sept. 2018. Available here
2. “Colloid.” Wikipedia, Wikimedia Foundation, 16 Sept. 2018. Available here