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This slide show covers the following course outcomes (refer to your
“Outcomes” handout for Unit 3):
› 3.1
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3.2
3.3
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3.4
3.5
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Complete the KWL chart below about pure substances and mixtures.
K
What you already know
W
What you wonder about
L
What you learned
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A pure substance is matter that is the same throughout.
According to the Particle Theory of Matter
(PTM):
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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.
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To consider pure substances, let’s consider our most important chemical:
water.
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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??
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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?
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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.
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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)
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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
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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.
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