Exploring Mixtures and their Separation
Kinds of mixtures
Sort mixtures into homogeneous and heterogeneous.
Separating mixtures is everyday science. It gives us sugar from sugarcane, and it lets a doctor test just a few drops of blood for malaria.
Mixtures come in two kinds:
- Homogeneous: the same all the way through. Stir sugar into water well, and the first sip and the last sip are equally sweet. This kind is called a solution. Vinegar (acetic acid in water) and soda (carbon dioxide in water) are solutions too.
- Heterogeneous: not the same all the way through. In sand and water you can see the sand, and it settles at the bottom. Oil and water are heterogeneous too.
Activity 5.1: three glasses that look similar. Stir salt into one glass of water, chalk powder into another, and a little milk into a third. Then ask four questions:
| Test | Salt water | Chalk water | Milk water |
|---|---|---|---|
| Can you see particles? | No | Yes | No |
| Can you see a laser beam's path from the side? | No | Yes | Yes |
| Does anything settle? | No | Yes | No |
| Does anything stay on the filter paper? | No | Yes | No |
(Never look straight into a laser beam.)
The results are different for each glass, so these are three different kinds of mixture:
- salt water is a solution;
- chalk water is a suspension;
- milk water is a colloid.
You will learn each one properly later in this chapter. For now, notice that mixtures that look alike can be quite different inside.
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