Lesson 7 — Activity 2:

Pure Substances and Mixtures



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Matter can be broken down into two categories: pure substances and mixtures. Pure substances are further broken down into elements and compounds. Mixtures are physically combined structures that can be separated into their original components. In this activity, you will learn more about pure substances and mixtures.

Everything you have or need to live can be classified into one of two categories:

  • pure substance
  • mixture

A pure substance is made of only one kind of matter and has a unique set of properties that is different than any other kind of matter. A pure substance may be either an element or a compound.


A compound is formed when two of more elements combine in specific, fixed amounts. For example, the water molecule you considered in Activity 1 is a compound of two hydrogen atoms and one oxygen atom. Pure water purchased in a store should have nothing else in the bottle except water molecules. Water not purchased in bottles may have lots of other elements such as iron, sulphur, and chlorine.


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A mixture is a combination of pure substances that do not combine chemically as they do when a compound is formed. The substances remain in their pure form, although they might not be easy to see.


There are four types of mixtures: mechanical mixture, solution, suspension, and colloid.

Mechanical mixture: The various substances that make up the mixture are clearly visible. An example of a mechanical mixture is a package of peas and carrots. They are together, but you can still see them separately in the package.

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Solution: The various substances that make up a solution are not visible. One substance dissolves in the other. Examples include sugar in coffee or carbon dioxide in a soft drink.

Suspension: In a cloudy mixture, tiny particles of one substance are held within another substance. An easy way to see if you have a suspension is to pour your liquid sample through some filter paper. If anything collects on the paper, you have a suspension. You might have a suspension if you put too many iced tea crystals in your glass of iced tea. Some will dissolve to make a solution, but wait a while, and you will see some of the particles sink to the bottom where they are no longer in suspension.

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Colloid: In some cloudy liquid mixtures, the particles of the suspended substance are too small to separate easily from the other substance. Milk is an example of a colloid.




Click on the Play button to watch a video that further explains pure substances and mixtures.

 



Digging Deeper

Click here to go to the Study Jams! website to watch a video. When you have finished watching the video, click on the "close" button in the upper right-hand corner to exit the video. Then, click on the "Test Yourself" button to see how much you know about mixtures.