Colloids: Definition, Types & Examples

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  • 0:01 What is a Colloid?
  • 0:23 Background Info on Solutions
  • 2:02 Types & Examples
  • 4:28 Lesson Summary
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Lesson Transcript
Instructor: Nadine James

Nadine has taught nursing for 12 years and has a PhD in Nursing research

In this lesson, you will learn the definition of colloids. There will be examples provided to assist you with your understanding of the topic. Also, several types of colloid solutions are provided.

What is a Colloid?

Colloids are important in both the natural environment and for manufactured products. A colloid is mixture where at least two types of substances are placed together. The substances, also called particles do not change; each substance retains its own properties. They do not settle out of the mixture and cannot be seen.

A colloid of two particles
mixture colloid

Background Information on Solutions

To understand more about what colloids are and aren't, it helps to first know a little more about two other types of mixtures: solutions and suspensions. A solution is made up of particles or solutes and a solvent. The solvent part of the solution is usually a liquid, but can be a gas. The particles are atoms, ions, or molecules that are very small in diameter.

Suspensions are also made up of particles and a solvent; however, its particles are larger than those found in a solution. The particles in a suspension can be distributed throughout the suspension evenly by shaking the mixture. However, the particles in a suspension do not remain distributed throughout the suspension - they will settle out.

Have you ever had a recipe that calls for mixing water and oil together? What happens? The water settles to the bottom and the oil rises to the top. You can mix them together, but in a few seconds after you stop mixing the oil will rise to the top again. This is an example of suspension.

A colloid mixture has particles that are not as small as a solution and not as large as a suspension. The particles are intermediate in size. What makes the colloid mixture unique is that the particles are assorted throughout pretty evenly and they stay that way.

Think of a solution as grade school, a colloid mixture as intermediate school, and a suspension as high school. The particles get larger as we move up the list of mixtures, just as students get larger in each school. So, how can you tell the difference between a solution, a suspension, and a colloid mixture?

Types and Examples

It is easy to tell the difference between a suspension and a colloid mixture. As stated earlier, the suspension, when mixed, will combine. But when mixing is stopped, the particles separate out. Remember the oil and water example?

So how can you tell if you have a solution or a colloid mixture? You can use the Tyndall effect, a test that can tell if you have a colloid mixture. If you have two glass beakers, you place the solution in one and the colloid mixture in another. Then, shine a light through both beakers. The light that passes through the solution will not be visible because the particles are so small. However, the light will be reflected off the larger particles of a colloid mixture. So you will be able to see the light.

To picture this more clearly, imagine that you are driving on a foggy night. What happens when you turn your headlights on? The water droplets scatter the light, making the headlight beams visible. That means one example of a colloid mixture is fog.

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