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Mixtures

You have already read that a pure substance has a uniform and

unchanging composition. What happens when two or more

substances are combined? A

mixture

is a combination of two or

more pure substances in which each pure substance retains its

individual chemical properties. The composition of mixtures is

variable, and the number of mixtures that can be created by

combining substances is infinite. Although much of the focus of

chemistry is the behavior of substances, it is important to

remember that most everyday matter occurs as mixtures.

Substances tend to mix naturally; it is difficult to keep any

substance pure.

Examine the mixtures in

Figure 19

. When oil, seasonings, and

vinegar are mixed, you can still distinguish all of the compo-

nents. If the mixture remains undisturbed long enough, the oil

will form a layer on top of the vinegar. On the other hand, you

cannot distinguish between the components of the mercury-silver mixture. You could, however, separate them by heating

the mixture. The mercury will evaporate before the silver does,

and you will obtain two separate substances: mercury vapor and

solid silver. The mercury and silver physically mixed to form the

mixture but did not chemically react with each other. They

could be separated by the physical method of boiling. The vapor

can be collected and condensed into liquid mercury.

Figure 19

There are different types of

mixtures. The components of some

mixtures, like this salad dressing, are

visible. It is not possible to see the different

components of some mixtures, such as this

mercury-silver filling.

FOCUS QUESTION

Would the substance still burn blue if it were mixed with

another substance?

LESSON 4

MIXTURES OF MATTER

Disciplinary Core Ideas

Crosscutting Concepts

Science & Engineering Practices

3D THINKING

COLLECT EVIDENCE

Use your Science Journal to

record the evidence you collect as

you complete the readings and

activities in this lesson.

INVESTIGATE

GO ONLINE

to find these activities and more resources.

Small-Scale Lab:

Separation of Aspirin

Carry out an investigation

to determine the

scale, proportion, and quantity

of the

components of a common medication.

Identify Crosscutting Concepts

Create a table of the

crosscutting concepts

and fill in examples you find as you read.

Module 2 • Matter—Properties and Changes