Table of Contents
Florida Benchmarks
Letter to the Student . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Test-Taking Checklist . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Next Generation Sunshine State Standards Correlation Chart . . . 7
Chapter 1
Understanding Science . . . . . . . . . . . . . . . . . . . . . . . 11
Lesson 1
Lesson 2
The Characteristics of
Scientific Knowledge . . . . . . . . . . . . . . . 12
SC.8.N.2.1, SC.8.N.2.2
Understanding Scientific Investigation . . 16
SC.8.N.1.1, SC.8.N.1.5,
SC.8.N.1.6
Lesson 3
Repeated Trials and Replication. . . . . . . 21
SC.8.N.1.1, SC.8.N.1.2,
SC.8.N.1.4
Lesson 4
Interpreting and Displaying Results . . . . 25
SC.8.N.1.1, SC.8.N.1.6,
SC.8.N.3.1
Lesson 5
Drawing Conclusions . . . . . . . . . . . . . . . 33
SC.8.N.1.1, SC.8.N.1.3
Lesson 6
Modifying and Revising Theories . . . . . . 38
SC.8.N.1.6, SC.8.N.3.2
Lesson 7
Science and Society . . . . . . . . . . . . . . . . 42
SC.8.N.4.1, SC.8.N.4.2
Chapter 1 Review . . . . . . . . . . . . . . . . . . . . . . . . . . 46
Chapter 2
Our Solar System . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
Lesson 8
Historical Knowledge of Our
Solar System. . . . . . . . . . . . . . . . . . . . . . 52
SC.8.E.5.8
Lesson 9
Gravity . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
SC.8.E.5.4
Lesson 10
Properties of the Sun . . . . . . . . . . . . . . . 60
SC.8.E.5.6
Lesson 11
The Objects of Our Solar System . . . . . . 64
SC.8.E.5.7
Lesson 12
Earth in the Solar System . . . . . . . . . . . . 69
SC.8.E.5.9
Lesson 13
The Effects of Earth’s Moon on Earth . . 73
SC.8.E.5.9
Lesson 14
Relative Positions of the Sun,
Earth, and Moon . . . . . . . . . . . . . . . . . . . 77
SC.8.E.5.9
Chapter 2 Review . . . . . . . . . . . . . . . . . . . . . . . . . . 81
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Chapter 3
Outer Space . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
Lesson 15
Understanding Distances in Space . . . . 86
SC.8.E.5.1, SC.8.E.5.2,
SC.8.E.5.3
Lesson 16
Properties of Stars . . . . . . . . . . . . . . . . . 91
SC.8.E.5.5
Lesson 17
Applications of the
Electromagnetic Spectrum . . . . . . . . . . . 96
SC.8.E.5.11
Technology and Its Contributions
to Astronomy. . . . . . . . . . . . . . . . . . . . . 101
SC.8.E.5.10, SC.8.E.5.11
Space Exploration and Its Effects
on Florida . . . . . . . . . . . . . . . . . . . . . . . 105
SC.8.E.5.12
Lesson 18
Lesson 19
Chapter 3 Review . . . . . . . . . . . . . . . . . . . . . . . . . 108
Chapter 4
Properties of Matter . . . . . . . . . . . . . . . . . . . . . . . . . 113
Lesson 20
Physical Properties of Matter . . . . . . . . 114
SC.8.P.8.1, SC.8.P.8.2,
SC.8.P.8.3, SC.8.P.8.4
Lesson 21
Atomic Theory. . . . . . . . . . . . . . . . . . . . 119
SC.8.P.8.7
Lesson 22
The Periodic Table of Elements . . . . . . 123
SC.8.P.8.6
Lesson 23
Common Compounds. . . . . . . . . . . . . . 128
SC.8.P.8.5, SC.8.P.8.8
Lesson 24
Identifying Mixtures. . . . . . . . . . . . . . . . 132
SC.8.P.8.4, SC.8.P.8.9
Chapter 4 Review . . . . . . . . . . . . . . . . . . . . . . . . . 138
Chapter 5
Changes in Matter . . . . . . . . . . . . . . . . . . . . . . . . . . 143
Lesson 25
Comparing Physical and
Chemical Changes . . . . . . . . . . . . . . . . 144
SC.8.P.8.5, SC.8.P.8.9,
SC.8.P.9.2, SC.8.P.9.3
Lesson 26
Temperature and Changes in Matter . . 149
SC.8.P.8.1, SC.8.P.9.2
Lesson 27
The Law of Conservation of Mass . . . . 153
SC.8.P.9.1
Lesson 28
Acids, Bases, and Salts . . . . . . . . . . . . 158
SC.8.P.8.8
Lesson 29
Chemical Changes and Balance
in Living Systems . . . . . . . . . . . . . . . . . 163
SC.8.L.18.1, SC.8.L.18.2,
SC.8.L.18.3, SC.8.L.18.4
Chapter 5 Review . . . . . . . . . . . . . . . . . . . . . . . . . 169
Investigation 1: Separating Mixtures . . . . . . . . . . . . . . . . . . . . . . 175
Investigation 2: Exploring Acids and Bases. . . . . . . . . . . . . . . . . 183
Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191
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28
X
Acids, Bases, and Salts
SC.8.P.8.8
Getting the Idea
Key Words
ion
acid
base
pH scale
neutral
neutralization
reaction
salt
What do lemons and batteries have in common?
What do baking soda and soap have in common?
The answer is that lemons and batteries are acidic, while baking
soda and soap have properties of bases. In this lesson, you will
learn about acids and bases and explore what happens when they
mix together.
Acids and Bases
In everyday life, you might think of strong liquids that can eat
away or corrode objects as acids. However, this is not always the
case. There are scientific reasons why substances are either acids
or bases. These reasons depend on the atoms that make up the
substance and what the substances release when they dissolve in
water. Recall that a normal uncharged atom has the same number
of electrons as its number of protons. However, some atoms have
more or less electrons. An ion forms when an atom gains or loses
electrons and becomes electrically charged.
Acids
An acid is any substance that releases hydrogen ions (H+)
in solution. Acids can easily be recognized by their chemical
formulas. Acids generally have formulas whose first element is
H. For example, HCl is hydrochloric acid, the acid present in
the human stomach. H2SO4 is sulfuric acid, an acid present in
batteries.
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Lesson 28: Acids, Bases, and Salts
Did You Know
Indicators are
used to identify
acidic and basic
substances. An
indicator is a
substance that
changes color in
the presence of
an acid or a base.
Some indicators
are red and blue
litmus paper, red
cabbage juice,
bromthymol blue,
and pH paper.
Acids have properties that make them different from other
substances. Have you ever tasted a slice of lemon or a lime? A
property of acids is a sour taste. Lemons, limes, and other citrus
fruits contain citric acid. Vinegar is an acid. Foods such as pickles
are soaked in vinegar, which is why they also taste sour.
JUICE
Carbonated
SODA
VINEGAR
ES
PICKL
Vitamin
C
Some acids can be harmful. Strong acids are corrosive, which
means they can eat through plastics, clothing, and even skin.
Acids can also eat through some metals. For this reason, you
should never touch or taste acids if you are unfamiliar with them.
Even if you think it is safe, never taste a sample unless you are
told to do so by a trusted adult such as your teacher.
Bases
A base is any substance that releases hydroxide ions (OH–) in
solution. Many bases have chemical formulas that end in OH.
For example, NaOH is sodium hydroxide, a base used in drain
cleaner. Calcium hydroxide, Ca(OH)2, is a base used to make
fertilizers, plaster, and cement.
Bases have many properties that make them different from other
substances. Bases taste bitter. They also feel slippery. A good
example of a base is soap. If you have ever accidentally tasted
soap, you know that it has a very bitter taste. Soap is also very
slippery. Another example of a base is baking soda.
FERTILIZER
SOAP
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DISH
LIQUID
BAKING
SODA
IN
DRA ER
AN
CLE
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Although bases are in some ways the “opposite” of acids, this
does not mean that they are never dangerous. Like acids, some
bases can be harmful. Strong bases are as corrosive as strong
acids and can eat through many materials. It is important that you
never touch or taste a base if you are unfamiliar with it. The table
below summarizes the characteristics of acids and bases.
Properties of Both
Acids and Bases
Properties of Acids
Taste sour
Can cause burns if
concentrated; handle
with care
Release H+ ions
React with metals to
produce hydrogen
gas bubbles
Can conduct electric
current when mixed
with water
Have a pH <7
React chemically
when mixed together
Turn blue litmus
paper red
Properties of Bases
Taste bitter
Release OH– ions
Feel slippery to the
touch
Have a pH >7
Turn red litmus paper
blue
pH Scale
3
4
5
6
7
8
Acid
NaOH
2
Soap
Lemon
juice
1
Pure
water
HCl
The strength of an acid or base is identified by a number
from 0 through 14. This number is called its pH. The pH scale
runs from 0 to 14, with low numbers being stronger acids, high
numbers being strong bases, and the number 7 being neutral,
neither an acid or a base. Hydrochloric acid in water forms a
very strong acid with a pH of 1. Sodium hydroxide in water
forms a strong base that has a pH of about 13. This is the active
ingredient in many household drain cleaners. Pure water is a
neutral substance with a pH of 7. Neutral substances do not share
properties with either acids or bases.
9
10
11
12
13
14
Base
Neutral
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Lesson 28: Acids, Bases, and Salts
When Acids and Bases Mix
Most liquids you come into contact with are either acids or bases.
A neutralization reaction is a chemical reaction in which an
acid and a base mix, react chemically, and form both water and
a salt. A salt is a solid compound that forms when an ion of a
metal replaces the hydrogen ion of an acid. During a neutralization
reaction, the H+ ions bond with the OH− ions. Together the ions
become water (H2O) with a pH of 7. The remaining atoms join
together to form a salt. A few typical neutralization reactions are
as follows:
HCl (acid) + NaOH (base) ➔ NaCl (a salt) + H2O (water)
H2SO4 (acid) + Ca(OH)2 (base) ➔ CaSO4 (a salt) + 2(H2O) (water)
KNO3 (acid) + KOH (base) ➔ KNO3 (a salt) + H2O (water)
Each example above shows that mixing an acid and a base
together produces a different type of salt and water.
DISCUSSION QUESTION
Many environmentally-friendly Web sites suggest making your own
drain cleaner of white vinegar, lemon juice, baking soda, and very hot
water. What do you think might make a homemade drain cleaner like
this effective?
LESSON REVIEW
1.
Which of the following substances is a base?
A.
vinegar
B.
lemon juice
C.
water
D.
liquid soap
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2.
3.
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An unknown substance is dissolved in water. The solution is
corrosive, conducts electricity, and has a higher concentration of
H+ ions than OH– ions. What kind of solution does this unknown
substance form?
A.
an acidic solution
B.
a basic solution
C.
a neutral solution
D.
There is no way to tell whether it is an acid or a base.
Citrus fruits generally have a pH less than 7. Based on this
information, you can say that these citrus fruits are
A.
neutral.
B.
acids.
C.
bases.
D.
electrically charged.
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