Mixtures

What are mixtures?

Mixtures are all around us: air, sea water, rock, soil, concrete, steel, milk, shampoo and paint, just to name a few.

All mixtures can be separated into their components, though it's sometimes very difficult. And sometimes the components are also mixtures themselves, like the vinegar in a macaroni salad.

But if you separate vinegar into its components you'll get two substances that are not mixtures: water and acetic acid. We call unmixed substances like this pure.

A pure substance is made up of only one type of stuff. Examples include purified water, oxygen, carbon dioxide, iron, diamond, table salt and vitamin C. Ultimately, all mixtures can be analysed into different combinations of pure substances.

It's often difficult to recognize a pure substance just by looking at it. Many mixtures have a uniform appearance, meaning that any part of them looks the same

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Pure substance

Write the following into your glossary

Mixture: A combination of two or more substances that can be physically separated.
Pure Substance: A substance that contains only one type of stuff.
Components: Parts of a mixture.

One way to represent pure substances and mixtures is using a particle model.

A pure substance contains only one type of particle. A mixture contains more than one type of particle.

For example, gold is a pure substance. It's made up of many particles of the same type.

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The particle model

Mixtures can be made from any combination of solids, liquids and gases. The "particles" in a mixture might be solid fragments, liquid droplets or gas bubbles.

Mixing these different components together can produce substances with new properties. For example, foams are formed by mixing gas bubbles into a liquid and some foams can hold their shapes in the way that solids do.

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Properties of mixtures

Proportions - write a short definition in your glossary

In mixtures, proportions describe how much of each substance is combined to make the mixture. They determine the characteristics of the mixture. For example, in cooking, the proportions of different ingredients affect the taste of the dish. Similarly, in chemistry, proportions determine the concentration and properties of a solution. Getting the proportions right is important for achieving the desired outcome.

Pencils are produced with a wide range of hardnesses because this affects the darkness of the lines they produce. The softer the lead, the darker the line.

The hardness of the lead depends on the amount of clay in the mixture. The clay becomes hard when it's fired in the kiln, whereas the graphite remains soft. The table on the next slide shows how clay content relates to the standard HB scale – H stands for hardness and B stands for blackness.

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Proportions matter

In your Glossary you should have the following:

1. Mixture

2. Pure substance

3. Components

4. Proportions

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Check your work

Follow your teachers directions on where to find your quiz.

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Quiz time!