Pure substances vs. Mixtures

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1

This slide show covers the following course outcomes (refer to your

“Outcomes” handout for Unit 3):

3.1

3.2

3.3

3.4

3.5

2

Complete the KWL chart below about pure substances and mixtures.

K

What you already know

W

What you wonder about

L

What you learned

3

A pure substance is matter that is the same throughout.

According to the Particle Theory of Matter

(PTM):

All matter is made up of tiny particles.

The particles of one substance differ from the particles of other substances.

What does this mean for pure substances?

We can infer that the particles in a pure substance are identical while the particles in a mixture are different.

4

To consider pure substances, let’s consider our most important chemical:

water.

Most of you should recognize the chemical symbol H

2

O. What does this mean?

The symbol H oxygen (O).

2

O refers to the parts of a water particle: 2 parts hydrogen (H) to 1 part

So, if water contains hydrogen and oxygen, why is it considered a pure substance??

5

The fact that water is a pure substance stems from the definition. That is, it is a substance that is the same throughout.

Q: If you took 10 drops of clear water and looked at each drop under a microscope, what would you notice?

A: Each drop is exactly the same! (Fig.7.5)

Every water particle is identical – each particle contains 2 parts hydrogen and 1 part oxygen.

6

Now, consider tap water.

Q: How would a drop of tap water compare with a drop of pure water?

A: The drop of tap water would contain water particles (H

2

O) but would also contain different particles such as chlorine, salt, dirt, etc.

Since there is more than one type of particle, tap water is a mixture (see figure 7.7, p.237)

7

A pure substance is matter that is the same throughout.

Every particle in the substance is identical.

Examples: pure water, oxygen, carbon dioxide

A mixture is matter that contains more than one type of particle.

Examples: tap water, air, soup

8

Read pages 236-237.

Complete the “Reading Check” (#1-3) on page 237.

Complete the “L” column in the KWL chart to explain what you learned and to answer your “wondering” questions.

Research Question:

There are two types of pure substances:

elements and compounds. Define these terms and find a few common examples of each.

9

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