2.1
2.1
Properties of Matter
1
Connecting to Your World
Guide for Reading
The more than 1200 species
of bamboo belong to a family of grasses that includes wheat and corn.
In tropical regions, bamboo plants grow rapidly to great heights.
The tender shoots of some bamboo plants are a
favorite food of pandas. People use the
woody stems of mature plants to make
furniture, fishing rods, and flooring.
Because bamboo is inexpensive and
abundant, disposable chopsticks are
usually made from bamboo. Bamboo has
properties that make it a good choice for
use in chopsticks. It has no noticeable odor
or taste. It is hard, yet easy to split, and it is
heat resistant. In this section, you will learn how
properties can be used to classify and identify matter.
Key Concepts
• How can properties used to
describe matter be classified?
• Why do all samples of a
substance have the same
intensive properties?
• What are three states of matter?
• How can physical changes be
classified?
Vocabulary
mass
volume
extensive property
intensive property
substance
physical property
solid
liquid
gas
vapor
physical change
Describing Matter
Understanding matter begins with observation and what you observe
when you look at a particular sample of matter is its properties. Is a solid
shiny or dull? Does a liquid flow quickly or slowly? Is a gas odorless or does
it have a smell?
Properties used to describe matter can be classified as
extensive or intensive.
Reading Strategy
Using Prior Knowledge Before
you read, write a definition for the
term liquid. After you read this
section, compare and contrast
the definition of liquid in the text
with your original definition.
Extensive Properties Recall that matter is anything that has mass and
takes up space. The mass of an object is a measure of the amount of matter
the object contains. The mass of a bowling ball with finger holes is five or
six times greater than the mass of the bowling ball shown in Figure 2.1,
which is used to play a game called candlepins. There is also a difference in
the volume of the balls. The volume of an object is a measure of the space
occupied by the object. Mass and volume are examples of extensive properties. An extensive property is a property that depends on the amount of
matter in a sample.
Intensive Properties There are properties to consider when selecting a
bowling ball other than mass. Beginning bowlers want a bowling ball that is
likely to maintain a straight path. They use bowling balls with a hard surface made from polyester. Experienced bowlers want a bowling ball they
can curve, or hook, toward the pins. Often, they use a polyurethane ball,
which has a softer surface. Hardness is an example of an intensive property.
An intensive property is a property that depends on the type of matter in a
sample, not the amount of matter.
Objectives
2.1.1 Identify properties of matter
as extensive or intensive.
2.1.2 Define physical property and
list several common physical
properties of substances.
2.1.3 Differentiate among three
states of matter.
2.1.4 Describe a physical change.
Guide for Reading
Build Vocabulary
Section 2.1 Properties of Matter 39
Section Resources
Print
• Guided Reading and Study Workbook,
Technology
• Interactive Textbook with ChemASAP,
Section 2.1
• Core Teaching Resources,
Section 2.1 Review
• Transparencies, T10–T11
Animation 1, Assessment 2.1
• Go Online, Section 2.1
L2
Imagine a Picture Before students
read this section, have them visualize
the structure of solids, liquids, and
gases at the microscopic level. Then
have them compare their mental pictures with the drawings in Figure 2.3.
Reading Strategy
L2
Active Comprehension Read the first
paragraph of Describing Matter. Ask
students what they would like to know
about extensive and intensive properties. Students can look for answers as
they read the rest of Describing Matter.
2
Figure 2.1 This bowling ball and candlepin are
used in a game played mainly in New England.
FOCUS
INSTRUCT
Tell students that the characters on the
chopsticks translate as good fortune,
prosperity, longevity, and good health.
Why are bamboo chopsticks usually
disposable? (Bamboo is inexpensive
and abundant.) What characteristic
makes bamboo useful for cooking
tools? (It is heat resistant.)
Describing Matter
L2
Discuss
To help students distinguish extensive
from intensive, you may want to note
that the prefix in- can mean “within.”
Also, the related word extend often
refers to an increase in a dimension,
such as length, area, or time.
Matter and Change
39
Section 2.1 (continued)
TEACHER
Demo
Volume and Mass
L2
Purpose Students observe that air
takes up space and has mass.
Materials plastic syringe (50 mL or
larger), balance that reads to 0.01 g,
Erlenmeyer flask with tightly fitting
1-hole rubber stopper, funnel, water
Procedure Ask students whether or
not air takes up space and has mass.
Determine the mass of the empty
syringe. Then determine the mass
when the syringe is full of air. Subtract
the two masses to find the mass of air
in the syringe. Fit a stopper and funnel
into an Erlenmeyer flask. The equipment must be airtight. Quickly pour
water through the funnel.
Expected Outcome The mass of the
air will be about 0.06 g. Some water
will run into the flask (air can be compressed), but not very much, because
air takes up the space in the flask.
Identifying Substances
Figure 2.2 This gold falcon
standard from Egypt is about
3000 years old. The copper
kettles are about 150 years old.
Analyzing Data Which of the
properties listed in Table 2.1
could not be used to distinguish
copper from gold?
Checkpoint Which is a better conductor of electric current—gold or copper?
Identifying Substances
Use Visuals
Table 2.1
L1
Physical Properties of Some Substances
Table 2.1 Ask, What is the relationship between the state of a substance at room temperature and its
boiling point? (Substances that are
gases at room temperature have boiling
points below 20°C; liquids and solids
have boiling points above 20°C. ) Are
the properties listed in the table
intensive or extensive? (intensive)
FYI
Some texts use substance to describe
all materials and pure substance to
describe elements and compounds. In
this text, substance and pure substance
are synonyms. A sample of matter can
be described as pure if the amount of
impurities in the sample is negligible.
Download a worksheet on Physical
Properties of Matter for students
to complete, and find additional
teacher support from NSTA SciLinks.
40 Chapter 2
Each object in Figure 2.2 has a different chemical makeup, or composition.
The sculpture of a falcon is mainly gold. The kettles are mainly copper.
Matter that has a uniform and definite composition is called a substance.
Gold and copper are examples of substances, which are also referred to as
pure substances.
Every sample of a given substance has identical
intensive properties because every sample has the same composition.
Gold and copper have some properties in common, but there are differences besides their distinctive colors. Pure copper can scratch the surface of pure gold because copper is harder than gold. Copper is better than
gold as a conductor of heat or electric current. Both gold and copper are
malleable, which means they can be hammered into sheets without breaking. But gold is more malleable than copper. Hardness, color, conductivity,
and malleability are examples of physical properties. A physical property is
a quality or condition of a substance that can be observed or measured
without changing the substance’s composition.
Table 2.1 lists physical properties for some substances. The states of
the substances are given at room temperature. (Although scientists use
room temperature to refer to a range of temperatures, in this book it will be
used to refer to a specific temperature, 20°C.) Physical properties can help
chemists identify substances. For example, a colorless substance that was
found to boil at 100°C and melt at 0°C would likely be water. A colorless
substance that boiled at 78°C and melted at 117°C would most certainly
not be water. Based on Table 2.1, it would likely be ethanol.
Substance
State
Color
Neon
gas
colorless
Oxygen
gas
colorless
Chlorine
gas
greenish-yellow
Ethanol
liquid
colorless
Mercury
liquid
silvery-white
Bromine
liquid
reddish-brown
Water
liquid
colorless
Melting
point (°C)
249
218
101
117
39
7
0
Boiling
point (°C)
246
183
34
78
357
59
100
For: Links on Physical
Sulfur
solid
yellow
115
445
Properties of Matter
Visit: www.SciLinks.org
Web Code: cdn-1021
Sodium chloride
solid
white
801
1413
Gold
solid
yellow
1064
2856
Copper
solid
reddish-yellow
1084
2562
40 Chapter 2
Differentiated Instruction
L3
Gifted and Talented
Ask students to identify two states of matter
other than solid, liquid, and gas. Have students prepare an oral or written report
describing the general characteristics of
these states and the conditions under which
matter is likely to exist in these states.
(Plasmas are likely at extremely high temperatures; Bose-Einstein condensates are
possible at extremely low temperatures.)
Students should explain why these states
of matter are not common on Earth.
States of Matter
States of Matter
Depending on the circumstances, you use three different words to refer to
water—water, ice, and steam. Water, which is a common substance, exists
in three different physical states. So can most other substances.
Three
states of matter are solid, liquid, and gas. Certain characteristics that can
distinguish these three states of matter are summarized in Figure 2.3.
Animation 1 Relate the states
of matter to the arrangements
of their particles.
with ChemASAP
Liquids Look at Figure 2.3b. The particles in a liquid are in close contact
with one another, but the arrangement of particles in a liquid is not rigid or
orderly. Because the particles in a liquid are free to flow from one location
to another, a liquid takes the shape of the container in which it is placed.
However, the volume of the liquid doesn’t change as its shape changes. The
volume of a liquid is fixed or constant. Thus, a liquid is a form of matter that
has an indefinite shape, flows, yet has a fixed volume. Liquids are almost
incompressible, but they tend to expand slightly when heated.
Demo
TEACHER
Solid
Liquid
Gas
Definite shape
Definite volume
Not easily compressed
Indefinite shape
Definite volume
Not easily compressed
Indefinite shape
Indefinite volume
Easily compressed
c
b
Comparing Solids and Liquids L1
Purpose Students construct models
of a solid and liquid.
Materials foam balls or miniature
marshmallows
Procedure Use Figure 2.3 as a guide for
the three-dimensional models.
Expected Outcome The particles in
each model should be closely packed,
but the arrangement in the solid
should be orderly.
Solids A solid is a form of matter that has a definite shape and volume.
The shape of a solid doesn’t depend on the shape of its container. The
particles in a solid are packed tightly together, often in an orderly arrangement, as shown in Figure 2.3a. As a result, solids are almost incompressible;
that is, it is difficult to squeeze a solid into a smaller volume. In addition,
solids expand only slightly when heated.
a
Activity
CLASS
Figure 2.3 The arrangement of particles is different in solids,
liquids, and gases. a In a solid, the particles are packed closely
together in a rigid arrangement. b In a liquid, the particles are
close together, but they are free to flow past one another. c In
a gas, the particles are relatively far apart and can move freely.
Relating Cause and Effect Use the arrangements of their particles
to explain the general shape and volume of solids and gases.
States of Chocolate
L2
Purpose Students observe three states
of matter when chocolate is heated.
Materials Piece of solid chocolate, small
beaker, large beaker, boiling water
Safety Use a thermal mitt while handling the boiling water.
Procedure Show students pieces of
solid chocolate. Place them in a small
beaker surrounded by boiling water in a
larger beaker. After a few minutes, ask,
How many physical states can you
discern in the mixture? (three)
Expected Outcome Three states can be
discerned as the chocolate melts: solid,
liquid, and vapor. Remind students that
their ability to smell the chocolate
means that some components of the
mixture must have vaporized.
FYI
There is a formal definition of
compressibility in Section 14.1.
Section 2.1 Properties of Matter 41
Facts and Figures
Answers to...
Thixotropic Materials
Changes of state are typically associated
with changes in temperature. However, the
state of matter can also be affected by other
variables. Thixotropic materials are solidlike
materials that liquefy when subjected to
shearing forces. For example, many paints
are thixotropic; they thin out when brushed
on a surface and thicken when the brush
strokes stop, thus keeping the paint from
sliding off the wall! A shearing force has an
opposite effect on quicksand. Quick movements “thicken” the quicksand and make it
much more difficult for a person or animal
trapped in it to move. (A shearing force
causes two layers to slide in opposite directions along a plane of contact.)
Figure 2.2 State; both are solids.
Figure 2.3 Solids have a definite
shape and volume because their particles are in a rigid, orderly arrangement; gases have no definite shape or
volume because their particles are relatively far apart and can move freely.
Checkpoint
copper
Matter and Change
41
Section 2.1 (continued)
Gases Like a liquid, a gas takes the shape of its container. But unlike a liquid, a gas can expand to fill any volume. A gas is a form of matter that takes
both the shape and volume of its container. Look back at Figure 2.3c. As
shown in the model, the particles in a gas are usually much farther apart
than the particles in a liquid. Because of the space between particles, gases
are easily compressed into a smaller volume.
The words vapor and gas are sometimes used interchangeably. But
there is a difference. The term gas is used for substances, like oxygen, that
exist in the gaseous state at room temperature. (Gaseous is the adjective
form of gas.) Vapor describes the gaseous state of a substance that is generally a liquid or solid at room temperature, as in water vapor.
Physical Changes
L1
Use Visuals
Figure 2.4 Have students study the
photograph. Refer them to page R14 of
the Elements Handbook for data on
the properties of gallium. Ask, Is the
melting of gallium a reversible or
irreversible change? (reversible) What
is the physical state of gallium at
room temperature? (solid)
3
ASSESS
Evaluate Understanding
L2
To assess students’ knowledge of states
of matter, ask, How are three states of
matter involved when a candle burns?
Tell students to include the definitions
for each state. (Solid wax has a definite
shape and volume; the melted liquid wax
is shapeless and runs down the side of the
candle; the vapor that forms above the
wick has no shape.)
Physical Changes
Figure 2.4 The silvery substance
in the photograph is gallium,
which has a melting point of 30°C.
Inferring What can you infer
about the temperature of the
hand holding the gallium?
The melting point of gallium metal is 30°C. Figure 2.4 shows how heat from
a person’s hand can melt a sample of gallium. The shape of the sample
changes during melting as the liquid begins to flow, but the composition of
the sample does not change. Melting is an example of a physical change.
During a physical change, some properties of a material change, but the
composition of the material does not change.
Words such as boil, freeze, melt, and condense are used to describe
physical changes. So are words such as break, split, grind, cut, and crush.
However, there is a difference between these two sets of words. Each set
describes a different type of physical change.
Physical changes can be
classified as reversible or irreversible. Melting is an example of a reversible
physical change. If a sample of liquid gallium is cooled below its melting
point, the liquid will become a solid. All physical changes that involve a
change from one state to another are reversible. Cutting hair, filing nails,
and cracking an egg are examples of irreversible physical changes.
L1
Reteach
If possible, bring samples of some of
the substances listed in Table 2.1 to
class. Describe the physical properties
of selected samples and have students
practice identifying them by referring
to Table 2.1.
Elements
Checkpoint When should the term vapor be used instead of gas?
Handbook
2.1 Section Assessment
1.
2.
Key Concept Name two categories used to
classify properties of matter.
Key Concept Explain why all samples of a given
substance have the same intensive properties.
3.
Key Concept Name three states of matter.
4.
Key Concept Describe the two categories
used to classify physical changes.
5. Which property in Table 2.1 can most easily distin-
The melting point of indium is 157°C.
Both indium and gallium (30°C) have
relatively low melting points compared with gold (1064°C).
8. Explain why samples of gold and copper can
have the same extensive properties, but not the
same intensive properties.
Handbook
Read about the metal indium on page R16. What is
the melting point of indium? Which other metal has
a similar melting point—gallium or gold? Provide
data to support your answer.
guish sodium chloride from the other solids?
6. In what way are liquids and gases alike? In what
way are liquids and solids different?
7. Is the freezing of mercury a reversible or irrevers-
ible physical change? Explain your answer.
Assessment 2.1 Test yourself
on the concepts in Section 2.1.
with ChemASAP
42 Chapter 2
If your class subscribes to the
Interactive Textbook, use it to
review key concepts in Section 2.1.
with ChemASAP
42 Chapter 2
Section 2.1 Assessment
1. intensive and extensive properties
2. Every sample of a given substance has
the same chemical composition.
3. solid, liquid, gas
4. Physical changes are either reversible or
irreversible. Reversible changes can be
“undone,” or reversed. Irreversible
changes cannot be undone.
5. Color; sodium chloride is the only white
solid listed.
6. Liquids and gases have an indefinite
shape. The shape of a solid is definite; the
shape of a liquid is indefinite.
7. The freezing of mercury is reversible
because solid mercury can be melted.
8. Samples of gold and copper can have the
same mass and volume (extensive properties). They cannot have the same set of
intensive properties because they have
different chemical compositions.
Hanging By a Thread
Hanging by a Thread
Purpose
Spinnerets
(magnification: 110,0003)
This Technology & Society feature
builds on the discussion of technology
and biotechnology in Chapter 1, where
an operational definition of a gene was
given, and on the discussion of properties in Section 2.1.
Strands in a spider web are about one tenth the diameter
of a human hair. Yet a golden orb spider web can withstand
the impact of a insect, or even a small bird, flying at high
speed because the silk in the web’s frame and spokes is
stronger than steel, more elastic than nylon, and tougher
than rubber. Scientists are always looking for lightweight
materials with these properties, but they cannot set up
farms to harvest spider silk because a spider will fight to
defend its territory. Instead, scientists use biotechnology
to produce spider silk. Interpreting Diagrams Where are
the silk glands located in a spider?
Background
• Only about one-third of spider species
spin webs, but all spiders produce silk.
Different types of silk glands produce
silk used for wrapping prey, silk used
for wrapping eggs, non-sticky silk used
for draglines, and sticky strands or
droplets used for trapping prey.
• Silk is a composite of proteins, which
explains why the silk can be strong,
tough, and elastic.
• Semi-permanent webs of golden orb
spiders are large (40–80 cm diameter).
A cable of golden orb dragline silk that
is slightly thicker than a garden hose
would be strong enough to support
two jet planes full of passengers and
cargo without breaking.
• Historically, people have collected spider silk to catch fish or birds and to use
as bandages to stop blood flow from
wounds. Possible commercial applications of recombinant spider silk are for
sutures, biodegradable fishing lines,
soft body armor, and in composites.
Heart
Eyes
Lung
Mouth
Silk glands
Stomach
Spider anatomy A spider releases its silk
through spinnerets at the tip of its abdomen.
Inside each spinneret are tens or hundreds of
spigots. Silk travels from a silk gland through
a duct to a spigot. As the silk is released from
a spigot, it changes from a liquid to a solid.
Female Golden Orb Spider
Nephila clavipes
Body length: 24 mm to 40 mm
Spider silk from goat’s milk
Scientists have identified the
spider genes that contain the
instructions for producing
silk. When these genes are
transferred to goats, the goats
produce milk containing
spider silk. Scientists separate
the silk from the milk, purify it,
and spin it into fibers.
43
Answers to...
Interpreting Diagrams The silk
glands are in the spider’s abdomen.
Figure 2.4 Because gallium is shown
in the liquid state, the temperature of
the hand must be greater than 30°C.
Checkpoint
The term vapor
is used to refer to the gaseous state
of a substance that is usually a liquid
or solid at room temperature.
Matter and Change
43
2.2
2.2
1
FOCUS
Objectives
Guide for Reading
2.2.1 Categorize a sample of matter
as a substance or a mixture.
2.2.2 Distinguish between homogeneous and heterogeneous samples of matter.
2.2.3 Describe two ways that components of mixtures can be
separated.
Guide for Reading
Build Vocabulary
Reading Strategy
Key Concepts
• How can mixtures be classified?
• How can mixtures be
separated?
Vocabulary
mixture
heterogeneous mixture
homogeneous mixture
solution
phase
filtration
distillation
In 1848, gold was discovered
in California. This discovery led to a massive migration, or rush, of
people to California. Panning is one way to
separate gold from a mixture of gold and
materials such as sand or gravel. A pan
containing the mixture is placed underwater and shaken vigorously from left
to right. This motion causes heavier
materials, such as gold, to move to
the bottom of the pan and lighter
materials, such as sand, to move to the
top where they can be swept away. In
this section, you will learn how to classify
and separate mixtures.
Reading Strategy
L2
Word Forms Have students look up
the term homogenize and explain how
this process could be used to turn a
heterogeneous mixture into one that is
more homogeneous.
Building Vocabulary After you
read this section, explain the difference between homogeneous
and heterogeneous mixtures.
L2
Using Context Clues Tie the Reading
Strategy to the Build Vocabulary strategy. Have students use the definitions
of homogeneous and heterogeneous
mixtures to answer the question posed
in the Reading Strategy.
2
Mixtures
Figure 2.5 You can choose the
amount of each item you select
from a salad bar. So your salad is
unlikely to have the same
composition as other salads
containing the same items.
Classifying Mixtures
A salad bar, like the one in Figure 2.5, provides a range of items, such as
cucumbers and hot peppers. Customers choose which items to use in their
salads and how much of each item to use. So each salad has a different
composition. A mixture is a physical blend of two or more components.
Most samples of matter are mixtures. Some mixtures are easier to recognize than others. You can easily recognize chicken noodle soup as a mixture of chicken, noodles, and broth. Recognizing air as a mixture of gases is
more difficult. But the fact that air can be drier or more humid shows that
the amount of one component of air—water vapor—can vary. Chicken
noodle soup and air represent two different types of mixtures.
Based
on the distribution of their components, mixtures can be classified as
heterogeneous mixtures or as homogeneous mixtures.
INSTRUCT
After students read the introduction,
ask What is the result of panning?
(Gold is separated from a mixture of
materials.) What property is used to
separate the mixture? (heaviness of
the materials) Heavier and lighter are
used to compare the materials because
density isn’t discussed until Chapter 3.
Classifying Mixtures
Discuss
Section Resources
L2
Bring orange juice or liquid salad
dressing to class and compare the
properties of these mixtures to those
of pure water or pure NaCl. Explain that
mixtures are variable in composition.
44 Chapter 2
44 Chapter 2
Print
• Guided Reading and Study Workbook,
Section 2.2
• Core Teaching Resources,
Section 2.2 Review
• Transparencies, T12–T14
Technology
• Interactive Textbook with ChemASAP,
Problem-Solving 2.10, Assessment 2.2
Quick LAB
Quick LAB
Separating Mixtures
Separating Mixtures
Purpose
Procedure
To separate a mixture using
paper chromatography.
1. Use the marking pen to draw a line
across a strip of filter paper, as shown
in the drawing. The line should be
2 cm from one end of the strip.
Materials
• green marking pen
• filter paper strip
• metric ruler
• clear plastic tape
• pencil
• rubbing alcohol
• clear plastic drinking cup
• clear plastic wrap
Filter paper
Ink line
Alcohol
2. Tape the unmarked end of the filter
paper to the center of a pencil so that
the strip hangs down when the pencil
is held horizontally.
Analyze and Conclude
1. How did the appearance of the filter
paper change during the procedure?
3. Working in a well-ventilated room,
pour rubbing alcohol into a plastic
cup to a depth of 1 cm.
3. How could you use this procedure
to identify an unknown type of
green ink?
5. Observe the setup for 15 minutes.
Heterogeneous Mixtures In chicken noodle soup, the ingredients are
not evenly distributed throughout the mixture. There is likely to be more
chicken in one spoonful than in another spoonful. A mixture in which the
composition is not uniform throughout is a heterogeneous mixture.
Homogeneous Mixtures The substances in the olive oil and vinegar in
Figure 2.6 are evenly distributed throughout these mixtures. So olive oil
doesn’t look like a mixture. The same is true for vinegar. Vinegar is a mixture
of water and acetic acid, which dissolves in the water. Olive oil and vinegar
are homogeneous mixtures. A homogeneous mixture is a mixture in which
the composition is uniform throughout. Another name for a homogeneous
mixture is a solution. Many solutions are liquids. But some are gases, like
air, and some are solids, like stainless steel, which is a mixture of iron, chromium, and nickel.
The term phase is used to describe any part of a sample with uniform
composition and properties. By definition, a homogeneous mixture consists of a single phase. A heterogeneous mixture consists of two or more
phases. When oil and vinegar are mixed, they form layers, or phases, as
shown in Figure 2.6. The oil phase floats on the water phase.
Checkpoint How many phases are there in a homogeneous mixture?
Figure 2.6 Olive oil and vinegar are homogeneous
mixtures. The substances in these mixtures are
evenly distributed. When olive oil is mixed with
vinegar, they form a heterogeneous mixture with
two distinct phases.
English Learners
L1
Encourage English-learner students to
compile a glossary in which they define
each key term in English and in their native
language. Suggest that students also
include illustrations when appropriate.
After completing this activity, students
will be able to:
• separate the components of a mixture using paper chromatography.
Skills Focus Observing, inferring,
drawing conclusions
Prep Time 15 minutes
Advance Prep
• Cut the paper strips in advance to
save time. Strips of paper toweling
can be used in place of filter paper.
Class Time 25 minutes
Safety Rubbing alcohol is poisonous
and flammable. It is also an irritant
when inhaled. Keep containers covered and away from heat. If the room is
not well ventilated, use a fume hood.
Expected Outcome Bands of color
will separate on the filter paper.
Extension Students could repeat the
lab using different brands of markers,
different colors, or water in place of
rubbing alcohol.
Analyze and Conclude
Olive oil
Vinegar
1. Bands of colors appear as the alcohol moves up the paper.
2. The bands of colors indicate that
green ink is a mixture.
3. The color pattern of the unknown
ink can be compared with color patterns from known types of green ink.
L3
For Enrichment
Oil & vinegar
Section 2.2 Mixtures 45
Differentiated Instruction
Objective
2. What evidence is there that green ink
is a mixture?
4. Rest the pencil on the rim of the cup
so that the ink end of the strip touches
the rubbing alcohol, but does not
extend below its surface. Use plastic
wrap to cover the top of the cup.
L2
Facts and Figures
Chromatography
The basis of chromatography is the
partitioning of components between
a stationary phase and a moving phase
based on differences in solubility. The
components travel with different speeds in
the moving solvent.
Students can research Rf values of different dyes and how they are calculated (ratio of distance traveled by dye
to distance traveled by solvent). They
can then quantify this lab by calculating the Rf values of the dyes in the ink.
FYI
In Section 15.3, solutions, suspensions,
and colloids are compared.
Answers to...
Checkpoint
one
Matter and Change
45
Section 2.2 (continued)
CONCEPTUAL PROBLEM 2.1
Separating a Heterogeneous Mixture
CONCEPTUAL PROBLEM 2.1
Aluminum nails are used on trail markers so that if a tree is harvested, the nail
can be sliced through at the lumber
mill without causing injury to a worker.
Sometimes plastic signs are used to mark trails used by hikers or
vehicles. The sign in the photo is used to mark locations along a
trail where an all terrain vehicle (ATV) is permitted. Aluminum
nails are used to attach signs at eye level to trees or posts. How
could a mixture of aluminum nails and iron nails be separated?
1
Answers
Analyze Identify the relevant concepts.
9. Iron is magnetic; table salt is not.
Table salt will dissolve in water;
iron will not.
10. By lowering the temperature to
below the boiling point of each
gas, you could condense each substance and separate the gases.
Aluminum:
• metal
• gray color
• doesn’t dissolve
in water
• not attracted
Practice
Problems
to magnet
L2
Practice Problems
Practice Problems Plus
Classify the following mixtures as
homogeneous or heterogeneous.
a. granite rock (heterogeneous)
b. salt water (homogeneous)
c. paint (heterogeneous)
d. a silver ring (homogeneous)
•
•
•
•
separate iron filings from table salt?
with small amounts of other gases such as argon
and carbon dioxide. What property could you
use to separate the gases in air?
Problem Solving 2.10 Solve
Problem 10 with the help of an
interactive guided tutorial.
with ChemASAP
Separating Mixtures
If you have a salad containing an ingredient you don’t like, you can use a
fork to remove the pieces of the unwanted ingredient. Many mixtures are
not as easy to separate. To separate a mixture of olive oil and vinegar, for
example, you could decant, or pour off, the oil layer. Or you might cool
the mixture until the oil turned solid. The first method takes advantage of
the fact that oil floats on water. The second method takes advantage of a
difference in the temperatures at which the olive oil and vinegar freeze.
Differences in physical properties can be used to separate mixtures.
L2
Purpose Students will observe the
separation of iron filings from ironfortified breakfast cereal.
Materials iron-fortified breakfast
cereal, 400-mL beaker, distilled water,
magnetic stirrer with stirring bar
Safety Remind students not to eat
the cereal.
Procedure Place a stirring bar in a
400-mL beaker. Add about 30 g of
cereal to the beaker and add distilled
water until the beaker is about half full.
Using a magnetic stirrer, mix gently
for about 20 minutes. Retrieve the
stirring bar and observe the black iron
filings attached to it.
Expected Outcome Iron filings will
cover the stirring bar. They are added
to cereal as an iron supplement.
Explain that stomach acid changes the
iron into a form the body can use.
46 Chapter 2
Identify a property that can be used to separate
iron and aluminum objects. The ability to be
attracted by a magnet is a property that iron and
aluminum do not share. You could use a magnet
to remove the iron nails from a mixture of iron
and aluminum nails.
Iron:
metal
gray color
doesn’t dissolve
in water
attracted to magnet
10. Air is mainly a mixture of nitrogen and oxygen,
Demo
Metallic Breakfast
Solve Apply concepts to this situation.
9. What physical properties could be used to
Separating Mixtures
TEACHER
2
List properties of aluminum and iron.
Filtration The colander in Figure 2.7 can separate cooked pasta from
the cooking water. The water passes through the holes in the colander, but the
pasta does not. The holes, or pores, in a coffee filter are smaller than the
holes in a colander to retain coffee grains. But the holes are not small
enough to retain the particles in water. The process that separates a solid
from the liquid in a heterogeneous mixture is called filtration.
Figure 2.7 A colander is used to separate
pasta from the water in which it was cooked.
This process is a type of filtration.
46 Chapter 2
Facts and Figures
Distillation
A working distillation apparatus was
described in the writings of Maria of Alexandria, an alchemist who lived and worked
nearly two thousand years ago. The city of
Alexandria, located on the Nile River in North
Africa, was a world center of science and culture at that time. Maria of Alexandria is also
credited with inventing other chemical apparatus, such as the water bath, which to this
day bears her name: the bain marie.
Use Visuals
100°C
Cold water out
Condenser
Steam at
100°C
Tap water
(mixture)
Cold water in
Figure 2.8 A distillation can be
used to remove impurities from
water. As liquid water changes
into water vapor, substances
dissolved in the water are left
behind in the distillation flask.
Inferring What can you infer
about the boiling points of
substances dissolved in the
impure water?
Receiver
flask
Distilled
water
Distillation Tap water is a homogeneous mixture of water and sub-
Key Concept How are mixtures classified?
12.
Key Concept What type of properties can be
used to separate mixtures?
17. Describe a procedure that could be used to
separate a mixture of sand and table salt.
13. Explain the term phase as it relates to homoge-
neous and heterogeneous mixtures.
14. Classify each of the following as a homogeneous
or heterogeneous mixture.
food coloring
ice cubes in liquid water
mouthwash
mashed, unpeeled potatoes
a.
b.
c.
d.
3
ASSESS
L2
Have students identify five items that
fit each of the following categories.
a. substance
b. homogeneous mixture
c. heterogeneous mixture
d. solution
Have students select three items (one
each from categories b, c, and d). For
each item selected, students should
outline a method for separating the
components.
2.2 Section Assessment
11.
Figure 2.8 Review the distillation process, and describe the components of
the apparatus. Ask, What might be an
advantage to having a long condenser in a distillation apparatus?
(There would be more surface area on
which the vapor can condense.) Is distilled water that contains dissolved
gases a pure substance? (No, distilled
water is not pure unless the dissolved
gases are removed.)
Evaluate Understanding
stances that dissolved in the water. One way to separate water from the
other components in tap water is through a process called distillation. During a distillation, a liquid is boiled to produce a vapor that is then condensed into a liquid. Figure 2.8 shows an apparatus that can be used to
perform a small-scale distillation.
As water in the distillation flask is heated, water vapor forms, rises in the
flask, and passes into a glass tube in the condenser. The tube is surrounded
by cold water, which cools the vapor to a temperature at which it turns back
into a liquid. The liquid water is collected in a second flask. The solid substances that were dissolved in the water remain in the distillation flask
because their boiling points are much higher than the boiling point of water.
L1
Writing to Persuade Write a paragraph in support
of this statement: Dry tea is a mixture, not a substance. Include at least two pieces of evidence to
support your argument.
L1
Reteach
Explain that distillation can be used to
separate a mixture of gases. Show students the drawing of the fractional distillation of liquid air on R24 of the
Elements Handbook. Ask, What physical property is used to separate the
gases? (boiling point)
[icon] Writing Activity
15. How are a substance and a solution similar? How
are they different?
16. In general, when would you use filtration to sepa-
rate a mixture? When would you use distillation to
separate a mixture?
Assessment 2.2 Test yourself
on the concepts in Section 2.2.
with ChemASAP
Possible evidence includes the fact
that only some substances in the tea
leaves dissolve in water, and tea is
sold both with and without caffeine.
Section 2.2 Mixtures 47
Section 2.2 Assessment
11. as heterogeneous or homogeneous
12. differences in physical properties
13. A phase is any part of a sample with uniform composition. There is one phase in a
homogeneous mixture and two or more
phases in a heterogeneous mixture.
14. a. homogeneous b. heterogeneous
c. homogeneous d. heterogeneous
15. Both have a uniform composition throughout. A substance has a definite composition; a solution has a variable composition.
16. Filtration separates solids from a liquid in
a heterogeneous mixture. Distillation can
separate a liquid from substances dissolved in the liquid.
17. Add water to dissolve the salt. Pour the
resulting mixture onto a piece of closely
woven cloth. The sand will remain on the
cloth, and the salt solution will pass through.
Use evaporation to remove the water from
the salt solution, leaving solid salt behind.
If your class subscribes to the
Interactive Textbook, use it to
review key concepts in Section 2.2.
with ChemASAP
Answers to...
Figure 2.8 They are much higher
than the boiling point of water.
Matter and Change
47
2.3
2.3
1
Elements and Compounds
FOCUS
Objectives
Guide for Reading
2.3.1 Explain the difference between
an element and a compound.
2.3.2 Distinguish between a substance and a mixture.
2.3.3 Identify the chemical symbols
of elements, and name elements, given their symbols.
L2
Word Forms Compare the common
meanings of element, elemental, and
elementary in relation to the specific
use of element in chemistry. In their
broadest sense, the terms refer to fundamentals, first principles, or basics.
Reading Strategy
• How are elements and
compounds different?
• How can substances and
mixtures be distinguished?
• What do chemists use to
represent elements and
compounds?
Vocabulary
element
compound
chemical change
chemical symbol
Guide for Reading
Build Vocabulary
Key Concepts
Reading Strategy
Relating Text and Visuals As
you read, look at Figure 2.10.
Explain how this illustration helps
you understand the relationship
between different kinds of matter.
L2
Preview Before students read the section, have them preview the headings
to get an overall sense or the content.
2
Take two pounds of sugar, two
cups of boiling water, and one-quarter teaspoon of cream of tartar.
You have the ingredients to make spun sugar.
Add food coloring and you have the sticky,
sweet concoction sold at baseball games
and amusement parks as cotton candy.
Sugar is a substance that contains three
other substances—carbon, hydrogen,
and oxygen. In this section, you will
learn how substances are classified as
elements or compounds.
Distinguishing Elements and Compounds
Substances can be classified as elements or compounds. An element is the
simplest form of matter that has a unique set of properties. Oxygen and
hydrogen are two of the more than 100 known elements. A compound is a
substance that contains two or more elements chemically combined in a
fixed proportion. For example, carbon, oxygen, and hydrogen are chemically combined in the compound sucrose, the sugar in spun sugar. (Sometimes sucrose is referred to as table sugar to distinguish it from other sugar
compounds.) In every sample of sucrose there are twice as many hydrogen
particles as oxygen particles. The proportion of hydrogen particles to
oxygen particles in sucrose is fixed. There is a key difference between elements and compounds.
Compounds can be broken down into simpler substances by chemical means, but elements cannot.
Breaking Down Compounds Physical methods that are used to separate mixtures cannot be used to break a compound into simpler substances.
Boil liquid water and you get water vapor, not the oxygen and hydrogen that
water contains. Dissolve a sugar cube in water and you still have sucrose, not
oxygen, carbon, and hydrogen. This result does not mean that sucrose or
water cannot be broken down into simpler substances. But the methods
must involve a chemical change. A chemical change is a change that produces matter with a different composition than the original matter. Heating
is one of the processes used to break down compounds into simpler substances. The layer of sugar in Figure 2.9 is heated in a skillet until it breaks
down into solid carbon and water vapor. Can the substances that are
produced also be broken down?
INSTRUCT
Ask students if they have ever eaten
cotton candy. Ask those who have to
describe its properties. Explain that its
sweet taste is due to a sugar called
sucrose, which is a compound.
Figure 2.9 When table sugar is heated, it
goes through a series of chemical changes.
The final products of these changes are
solid carbon and water vapor.
Distinguishing Elements
and Compounds
Use Visuals
L1
Compare the chemical change of sugar
shown on R29 with the one shown in
Figure 2.9. Ask, What is similar about
the changes? (Sugar breaks down into
solid carbon and water vapor.) What is
different? (In one case, heating causes
the change; in the other, the addition of
an acid.) You can also compare the
electrolysis of water to the distillation
of water (Section 2.2).
48 Chapter 2
48 Chapter 2
Section Resources
Print
• Guided Reading and Study Workbook,
Section 2.3
• Core Teaching Resources, Section 2.3
Review, Interpreting Graphics
• Transparencies, T15–T17
Technology
• Interactive Textbook with ChemASAP,
Problem-Solving 2.19, Assessment 2.3
• Go Online, Section 2.3
There is no chemical process that will break down carbon into simpler
substances because carbon is an element. Heating will not cause water to
break down, but electricity will. When an electric current passes through
water, oxygen gas and hydrogen gas are produced. The following diagram
summarizes the overall process.
Chemical change
Sugar
heat
¡ Carbon Water
Compound
Element
Compound
Word Origins
Compound comes from a
Latin word componere,
meaning “to put together.”
Elements are put together,
or chemically combined, in
compounds. What items
are put together in a
compound sentence?
Chemical change
Water
¬¡
Compound
electricity
Hydrogen
Element
Oxygen
Element
Properties of Compounds In general, the properties of compounds
are quite different from those of their component elements. Sugar is a
sweet-tasting, white solid, but carbon is a black, tasteless solid. Hydrogen is
a gas that burns in the presence of oxygen—a colorless gas that supports
burning. The product of this chemical change is water, a liquid that can
stop materials from burning. Figure 2.10 shows samples of table salt
(sodium chloride), sodium, and chlorine. When the elements sodium and
chlorine combine chemically to form sodium chloride, there is a change in
composition and a change in properties. Sodium is a soft, gray metal. Chlorine is a pale yellow-green poisonous gas. Sodium chloride is a white solid.
Checkpoint What process can be used to break down water?
Chlorine is used to kill
harmful organisms in
swimming pools.
Figure 2.10 Compounds and
the elements from which they
form have different properties.
Observing Based on the
photographs, describe two
physical properties of sodium
and two of chlorine.
Sodium chloride
(commonly known as
table salt) is used to
season or preserve food.
Demo
TEACHER
Decomposition of Sugar
L2
Purpose Students will observe the
decomposition of sugar by acid.
Materials 100-mL beaker, powdered
sugar, 18M sulfuric acid, glass stirring rod
Safety Perform the demo in a fume
hood or in a well-ventilated area and
be sure to wear safety goggles.
CAUTION This is an extremely exothermic reaction.
Procedure Place about 25 g of powdered
sugar in a 100-mL beaker. Carefully add
about 10–15 mL of 18M sulfuric acid, and
stir rapidly with a glass rod.
Disposal Place the cooled beaker and
its contents in a large beaker and add
water. Neutralize with NaOH and pour
the liquid down the drain, flushing
with excess water. Throw the solid residue in the trash.
Expected Outcome The mixture turns
dark and a column of carbon rises out
of the beaker.
Word Origins
L2
A compound sentence contains two
independent clauses, each with a
subject and a verb. The two clauses
are joined by a conjunction.
L2
Relate
Refer students to Salt of the Earth on
page R9 of the Elements Handbook for
a discussion of the historic importance
of table salt.
Sodium is stored under
oil to keep it from
reacting with oxygen
or water vapor in air.
Sodium vapor produces
the light in some
street lamps.
FYI
Section 2.3 Elements and Compounds 49
In the Small-Scale lab in Chapter 21,
students will learn that the electrolysis
of water doesn’t work with pure water.
Differentiated Instruction
L3
Other forms of energy besides electricity can
be used to bring about the decomposition of
water into hydrogen and oxygen. Ask students to consider whether heat could be
used for this purpose. Tell them that early
chemists considered water to be an element
Gifted and Talented
because it would not decompose when
heated. Have students do research on the
conditions necessary to decompose water
using heat. What hazards, if any, might preclude the routine use of this method?
Answers to...
Figure 2.10 sodium: gray color,
shiny, solid at room temperature;
chlorine: yellow-green color, gas at
room temperature.
Checkpoint
passing an electric current through water
Matter and Change
49
Section 2.3 (continued)
Distinguishing Substances and Mixtures
Deciding whether a sample of matter is a substance or a mixture based
solely on appearance can be difficult. After all, homogeneous mixtures and
substances will both appear to contain only one kind of matter. Sometimes
you can decide by considering whether there is more than one version of
the material in question. For example, you can buy whole milk, low-fat
milk, no-fat milk, light cream, and heavy cream. From this information, you
can conclude that milk and cream are mixtures. You might infer that these
mixtures differ in the amount of fat they contain. Most gas stations offer at
least two blends of gasoline. The blends have different octane ratings and
different costs per gallon, with premium blends costing more than regular
blends. So gasoline must be a mixture.
You can use their general characteristics to distinguish substances
from mixtures.
If the composition of a material is fixed, the material
is a substance. If the composition of a material may vary, the material is
a mixture. Figure 2.11 summarizes the general characteristics of elements,
compounds, and mixtures.
Distinguishing
Substances and Mixtures
L1
Use Visuals
Figure 2.11 Have students study the
figure. Then ask, Can compounds be
separated into their component elements by physical processes? (No,
they must be separated by chemical
processes.)
CLASS
Substances
Activity
L2
Purpose To establish the definition of
substance, using an inductive approach.
Materials 20 index cards, masking
tape
Procedure Make signs with the names
of each of these items: 1 oxygen, 2 neon,
3 apple, 4 sand, 5 iron, 6 water, 7 air,
8 paint, 9 sodium chloride, 10 sucrose,
11 carbon dioxide, 12 granite, 13 laundry detergent, 14 citric acid, 15 cereal,
16 salad, 17 salad dressing, 18 copper,
19 ocean water, 20 gold. Using masking
tape and the board or wall, create two
columns. Place items 1 and 2 under
Column A and items 3 and 4 under
Column B. Ask students to think about
the criteria for each column. Then place
item 5 in Column A. Students may have
to change their criteria. Place item 6 in
Column A. Ask students what they think
the criteria are now. Continue placing
one item up at a time in a column until
students understand the criteria. Everything in Column A has a uniform and
definite composition.
Expected Outcome Column A is for
substances. Column A: 1, 2, 5, 6, 9, 10,
11, 14, 18, 20. Column B is for mixtures.
Column B: 3, 4, 7, 8, 12, 13, 15, 16, 17, 19.
Make sure students understand the
difference between the uniform composition of a substance and of a solution. The composition of the substance
is fixed. The composition of the mixture can vary.
50 Chapter 2
Figure 2.11 The flow chart
summarizes the process for
classifying matter. Any sample
of matter is either an element,
a compound, or a mixture.
Matter
Interpreting Diagrams
What is the key difference
between a substance and
a solution?
Can be separated
Silver physically
Substance
Definite composition
(homogeneous)
Can be separated
chemically
Element
Silver
Mixture of
substances
Variable composition
Compound
Homogeneous
mixture
Uniform; also
called a solution
Heterogeneous
mixture
Nonuniform;
distinct phases
Beryl
Stainless Steel
Granite
50 Chapter 2
Facts and Figures
Origins of Element Names
Many elements were named for the people
who discovered them or the places where
they were discovered. Some elements were
given descriptive names taken from classical
Latin or Greek. Others were named for figures
in mythology. Polonium is named for Poland,
the native land of Marie Curie, who discovered
radium. Californium was discovered at the
University of California. The name chlorine
comes from the Greek chloros, meaning
greenish-yellow. Chlorine is a greenish-yellow
gas. The name calcium is derived from the
Latin calx, meaning lime. Calcium is a major
component of limestone. Students can find
the origins of element names by consulting a
dictionary or encyclopedia.
CONCEPTUAL PROBLEM 2.2
CONCEPTUAL PROBLEM 2.2
Classifying Materials
Answers
When the blue-green solid in the photograph is heated, a colorless
gas and a black solid form. All three materials are substances. Is
it possible to classify these substances as elements or compounds?
18. Liquid A is probably a substance.
Liquid B is a mixture.
19. The liquid was not an element
because a solid was left when the
liquid evaporated. A physical process, such as evaporation, cannot
be used to break down a compound. Therefore, the liquid was a
mixture.
Analyze Identify the relevant concepts.
Solve Apply concepts to this situation.
List the known facts and relevant concepts.
• A blue-green solid is heated.
• A colorless gas and a black solid appear.
• A compound can be broken down into simpler
substances by a chemical change, but an
element cannot.
• Heating can cause a chemical change.
Determine if the substances are elements or
compounds. Before heating, there was one substance. After heating there were two substances.
The blue-green solid must be a compound.
Based on the information given, it isn’t possible
to know if the colorless gas or black solid are
elements or compounds.
Practice Problems
18. Liquid A and Liquid B are clear liquids. They
19. A clear liquid in an open container is allowed to
are placed in open containers and allowed to
evaporate. When evaporation is complete,
there is a white solid in container B, but no
solid in container A. From these results, what
can you infer about the two liquids?
evaporate. After three days, a solid is left in the
container. Was the clear liquid an element, a
compound, or a mixture? How do you know?
Problem Solving 2.19 Solve
Problem 19 with the help of an
interactive guided tutorial.
Symbols and Formulas
The common names water and table salt do not provide information about
the chemical composition of these substances. Also, words are not ideal for
showing what happens to the composition of matter during a chemical
change.
Chemists use chemical symbols to represent elements, and
chemical formulas to represent compounds.
Using symbols to represent different kinds of matter is not a new idea.
Figure 2.12 shows some symbols that were used in earlier centuries. The
symbols used today for elements are based on a system developed by a
Swedish chemist, Jöns Jacob Berzelius (1779–1848). He based his symbols
on the Latin names of elements. Each element is represented by a one- or
two-letter chemical symbol. The first letter of a chemical symbol is always
capitalized. When a second letter is used, it is lowercase.
Lead
Salt
Zinc
Gravel
Tin
Clay
Alchemy Symbols
Carbon
Gold
Oxygen
Dalton‘s Symbols
Zinc
with ChemASAP
Less Proficient Readers/
English Learners
L1
Have students make flash cards to help learn
the names and symbols of at least 30 elements. If an element has a different common
name in the student’s native country, have
the student include that information on the
flash card.
L2
Classify the following materials as
an element, compound, or mixture.
Give reasons for your answers.
a. table salt (NaCl) (compound; its formula shows that it is composed of at
least two elements)
b. salt water (mixture; its name suggests that it is composed of at least
two substances)
c. sodium (Na) (element; its symbol
shows that it is composed of only one
kind of matter)
Symbols and Formulas
L2
Discuss
Figure 2.12 The symbols used
to represent elements have
changed over time. Alchemists
and the English chemist John
Dalton (1766–1844) both
used drawings to represent
chemical elements. Today,
elements are represented by
one- or two-letter symbols.
Section 2.3 Elements and Compounds 51
Differentiated Instruction
Practice Problems Plus
Point out that the use of chemical symbols is an example of the “international
language of chemistry.” Discuss why
people all over the world use the same
set of chemical symbols. Show how
symbols are used in chemical formulas.
Emphasize that a compound is always
made up of the same elements in the
same proportions.
Activity
CLASS
L2
To help students explore the history of
science, have the class work as a group
to make a timeline for the discovery of
elements. Refer them to the data on
dates of discovery in the Elements
Handbook. Students could use the
timeline to detect shifts in naming
conventions.
Timeline of Discovery
Answers to...
Figure 2.11 The composition of a
substance is fixed; the composition of
a solution may vary.
Matter and Change
51
Section 2.3 (continued)
Table 2.2
Symbols and Latin Names for Some Elements
Name
Download a worksheet on Element
Names for students to complete,
and find additional teacher support
from NSTA SciLinks.
3
For: Links on Element
L2
Names
Visit: www.SciLinks.org
Web Code: cdn-1023
Ask students to explain in their own
words the difference between an
element and a compound.
Reteach
L1
Set up a display of elements in the
classroom to help students relate
abstract chemical symbols to actual
samples. Have students present oral
reports about the physical properties
of elements and refer to the display.
[icon] Writing Activity
Elements and compounds are alike
in that they both are substances of
fixed composition. They are different
in that elements cannot be separated into simpler substances
through chemical changes.
Latin name
natrium
kalium
stibium
cuprum
aurum
argentum
ferrum
plumbum
stannum
2.3 Section Assessment
20.
Key Concept How is a compound different
from an element?
21.
Key Concept How can you distinguish a
substance from a mixture?
22.
Key Concept What are chemical symbols
and chemical formulas used for?
27. What elements make up the pain reliever
acetaminophen, chemical formula C8H9O2N?
Which element is present in the greatest
proportion by number of particles?
23. Name two methods that can be used to break
down compounds into simpler substances.
24. Classify each of these samples of matter as an
element, a compound, or a mixture.
b. tap water
d. nitrogen
a. table sugar
c. cough syrup
Compare and Contrast Paragraph Compare and
contrast elements and compounds. Compare them
by saying how they are alike. Contrast them by
describing how they are different.
25. Write the chemical symbol for each element.
a. hydrogen
b. oxygen
c. silver
d. sodium
e. hydrogen
f. aluminum
26. Name the chemical elements represented by the
following symbols.
a. C
b. Ca
c. K
If your class subscribes to the
Interactive Textbook, use it to
review key concepts in Section 2.3.
Na
K
Sb
Cu
Au
Ag
Fe
Pb
Sn
If the English name and the Latin name of an element are similar, the
symbol will appear to have been derived from the English name. Examples
include Ca for calcium, N for nitrogen, and S for sulfur. Table 2.2 shows
examples of elements where the symbols do not match the English names.
Chemical symbols provide a shorthand way to write the chemical formulas of compounds. The symbols for hydrogen, oxygen, and carbon are
H, O, and C. The formula for water is H2O. The formula for sucrose, or table
sugar, is C12H22O11. Subscripts in chemical formulas are used to indicate the
relative proportions of the elements in the compound. For example, the
subscript 2 in H2O indicates that there are always two parts of hydrogen for
each part of oxygen in water. Because a compound has a fixed composition, the formula for a compound is always the same.
ASSESS
Evaluate Understanding
Symbol
Sodium
Potassium
Antimony
Copper
Gold
Silver
Iron
Lead
Tin
d. Au
e. Fe
f. Cu
Assessment 2.3 Test yourself
on the concepts in Section 2.3.
with ChemASAP
52 Chapter 2
with ChemASAP
Section 2.3 Assessment
20. Compounds can be broken down into
simpler substances by chemical means,
but elements cannot.
21. A substance has a fixed composition. The
composition of a mixture may vary.
22. Chemical symbols are used to represent
elements. Chemical formulas are used to
represent compounds.
23. heating or an electric current
52 Chapter 2
24. a. compound b. mixture
c. mixture d. element
25. a. H b. O c. Ag d. Na e. H f. Al
26. a. carbon b. calcium c. potassium
d. gold e. iron f. copper
27. Carbon, hydrogen, oxygen, and nitrogen;
hydrogen is present in the greatest proportion by number of atoms.
2.4
2.4
Chemical Reactions
1
Connecting to Your World
Guide for Reading
Iron is an element with many
desirable properties. It is abundant, easy to shape when heated,
and relatively strong, especially when mixed with carbon in steel.
Iron has one main disadvantage. Over time,
objects made of iron will rust if they are
left exposed to air. The brittle layer of rust
that forms on the surface of the object
flakes off, exposing more iron to the air.
In this section, you will learn to recognize
chemical changes and to distinguish them
from physical changes.
Key Concepts
• What always happens during a
chemical change?
• What are four possible clues
that a chemical change has
taken place?
• How are the mass of the
reactants and the mass of the
products of a chemical reaction
related?
Vocabulary
chemical property
chemical reaction
reactant
product
precipitate
law of conservation of mass
Chemical Changes
The compound formed when iron rusts is iron oxide (Fe2O3). Words such as
burn, rot, rust, decompose, ferment, explode, and corrode usually signify a
chemical change. The ability of a substance to undergo a specific chemical
change is called a chemical property. Iron is able to combine with oxygen to
form rust. So the ability to rust is a chemical property of iron. Chemical
properties can be used to identify a substance. But chemical properties can
be observed only when a substance undergoes a chemical change.
Figure 2.13 compares a physical change and a chemical change that
can occur in a mixture of iron and sulfur. When a magnet is used to separate iron from sulfur, the change is a physical change. The substances
present before the change are the same substances present after the
change, although they are no longer physically blended. Recall that during
a physical change, the composition of matter never changes.
During a
chemical change, the composition of matter always changes. When the mixture of iron and sulfur is heated, a chemical change occurs. The sulfur and
iron react and form iron sulfide (FeS).
A chemical change is also called a chemical reaction. One or more substances change into one or more new substances during a chemical reaction.
A substance present at the start of the reaction is a reactant. A substance
produced in the reaction is a product. In the reaction of iron and sulfur,
iron and sulfur are reactants and iron sulfide is a product.
Reading Strategy
Predicting Before you read,
predict what will happen to the
mass of a sample of matter that
burns. After you read, check the
accuracy of your prediction and
correct any misconceptions.
a
FOCUS
Objectives
2.4.1 Describe what happens during
a chemical change.
2.4.2 Identify four possible clues
that a chemical change has
taken place.
2.4.3 Apply the law of conservation
of mass to chemical reactions.
Guide for Reading
Build Vocabulary
L2
Compare and Contrast Table Have
students make a table to compare
physical and chemical changes.
Reading Strategy
L2
Predict Before students read the section, have them predict the meanings of
reactant and product. Ask students what
they are basing their predictions on.
2
INSTRUCT
What evidence do you see in the
photo that a chemical reaction has
occurred? (The metal has changed color.)
Chemical Changes
Use Visuals
Figure 2.13 A mixture of iron filings and sulfur
can be changed. a A magnet separates the iron
from the sulfur. b Heat combines iron and sulfur
in a compound. Classifying Which change is a
chemical change? Explain.
b
Section 2.4 Chemical Reactions 53
Section Resources
Print
• Guided Reading and Study Workbook,
Section 2.4
• Core Teaching Resources,
Section 2.4 Review
• Transparencies, T18–T19
• Laboratory Manual, Labs 2–3
• Laboratory Practicals, 2-1
• Small-Scale Chemistry Laboratory
Manual, Lab 2
Technology
• Interactive Textbook with ChemASAP,
Assessment 2.4
• Go Online, Section 2.4
L1
Figure 2.13 Discuss the difference
between physical and chemical
changes. Ask, What substances are
present before and after the change
in photo a? (iron and sulfur) What substances are present before and after
the change in photo b? (iron and sulfur before, iron sulfide after )
FYI
The Roman numerals were omitted
from iron(III) oxide and iron(II) sulfide
to avoid having to explain the Stock
system, which is explained on p. 254.
Answers to...
Figure 2.13 b; A new substance is
formed.
Matter and Change
53
Section 2.4 (continued)
Recognizing Chemical Changes
Recognizing Chemical
Changes
For: Links on Chemical
TEACHER
Demo
and Physical
Changes
Visit: www.SciLinks.org
Web Code: cdn-1024
Identifying a Chemical Change L2
Purpose Students will practice
identifying chemical changes.
Materials Bunsen burner, match,
tongs, magnesium ribbon, 4 test tubes,
solutions of 0.1M AgNO3, 0.1M NaCl,
0.1M K2CrO4, and 3M H2SO4, mossy
zinc, marble chip, spatulas, cobalt blue
glass filters
Safety For Step 3, wear gloves to avoid
stains on your skin from silver nitrate.
CAUTION Students should not look at
burning magnesium without the cobalt
blue glass filters.
Procedure As you do each step, have
students identify the clue for chemical
change. Emphasize that the clues point
to a chemical change but do not
confirm that a change has taken place.
a. Light a Bunsen burner. (heat and
light produced)
b. Using tongs, hold a piece of magnesium ribbon in a burner flame until it
ignites. Remove from heat and
observe. (The product is a white powder; heat and light are produced.)
c. Put 5 mL of silver nitrate solution in
each of two test tubes. Add a small
amount of sodium chloride solution
to one tube and potassium chromate solution to the other. (color
change, formation of a precipitate)
d. Put 5 mL of the sulfuric acid in each
of two test tubes. Add a piece of
mossy zinc to one tube and a marble
chip (CaCO3) to the other. (formation
of a gas)
Figure 2.14 Clues to chemical
change often have practical
applications. a Bubbles of
carbon dioxide gas form when a
geologist puts acid on a rock
that contains compounds called
carbonates. b When a test strip
is dipped in urine, the color
change is used to estimate the
level of the sugar glucose in
urine. c One step in the production of cheese is a reaction
that causes milk to separate into
solid curds and liquid whey.
How can you tell whether a chemical change has taken place? There are
four clues that can serve as a guide.
Possible clues to chemical change
include a transfer of energy, a change in color, the production of a gas, or
the formation of a precipitate.
Every chemical change involves a transfer of energy. For example,
energy stored in natural gas is used to cook food. When the methane in natural gas combines with oxygen in the air, energy is given off in the form of
heat and light. Some of this energy is transferred to and absorbed by food
that is cooking over a lit gas burner. The energy causes chemical changes to
take place in the food. The food may brown as it cooks, which is another
clue that chemical changes are occurring.
You can observe two other clues to chemical change while cleaning a
bathtub. The ring of soap scum that can form in a bathtub is an example of
a precipitate. A precipitate is a solid that forms and settles out of a liquid
mixture. Some bathroom cleaners that you can use to remove soap scum
start to bubble when you spray them on the scum. The bubbles are a product of a chemical change that is taking place in the cleaner.
If you observe a clue to chemical change, you cannot be certain that a
chemical change has taken place. The clue may be the result of a physical
change. For example, energy is always transferred when matter changes
from one state to another. Bubbles form when you boil water or open a
carbonated drink. The only way to be sure that a chemical change has
occurred is to test the composition of a sample before and after the change.
Figure 2.14 shows examples of practical situations in which different clues
to chemical change are visible.
Checkpoint What energy transfer takes place when food cooks?
b
c
a
54 Chapter 2
Facts and Figures
Urinalysis Test Strips
Download a worksheet on Chemical and Physical Changes for students to complete, and find
additional teacher support from
NSTA SciLinks.
54 Chapter 2
A test-strip urinalysis is semi-quantitative,
meaning that the test provides information
about the level of a material present in the
urine, but not a specific quantity. The strips
can also be used to test for ketones, protein,
blood, nitrite, bilirubin, urobilinogen, pH,
white blood cells, and specific gravity. All the
tests involve a color change.
In one glucose test, the hydrogen peroxide
produced when glucose is oxidized reacts
with potassium iodide. The oxygen produced
in the second reaction binds with a dye to
produce colors that range from blue to
dark brown. You may want to relate what
happens with test strips to what happens in
the Small-Scale lab on p. 56.
a
b
Conservation of Mass
L1
Use Visuals
Figure 2.15 When the liquids in
photograph A are mixed, they
react. None of the products are
gases. Analyzing Data How do
you know that a reaction took
place and that mass was conserved during the reaction?
Conservation of Mass
3
When wood burns, substances in the wood combine with oxygen from the
air. As the wood burns, a sizable amount of matter is reduced to a small pile
of ashes. The reaction seems to involve a reduction in the amount of matter. But appearances can be deceiving.
During any chemical reaction,
the mass of the products is always equal to the mass of the reactants. Two
of the products of burning wood—carbon dioxide gas and water vapor—
are released into the air. When the mass of these gases is considered, the
amount of matter is unchanged. Careful measurements show that the total
mass of the reactants (wood and the oxygen consumed) equals the total
mass of the products (carbon dioxide, water vapor, and ash).
Mass also holds constant during physical changes. For example, when
10 grams of ice melt, 10 grams of liquid water are produced. Similar observations have been recorded for all chemical and physical changes studied.
The scientific law that reflects these observations is the law of conservation
of mass. The law of conservation of mass states that in any physical change
or chemical reaction, mass is conserved. Mass is neither created nor
destroyed. The conservation of mass is more easily observed when a
change occurs in a closed container, as in Figure 2.15.
Key Concept How does a chemical change
affect the composition of matter?
29.
Key Concept Name four possible clues that
a chemical change has taken place.
30.
Key Concept In a chemical reaction, how
does the mass of the reactants compare with the
mass of the products?
31. What is the main difference between physical
changes and chemical changes?
ASSESS
Evaluate Understanding
L2
Write this word equation on the board.
methane + oxygen →
carbon dioxide + water + energy
Have students identify the reactants
and products and one possible clue for
a chemical change.
L1
Reteach
Write a word equation on the board for
the reaction of magnesium and oxygen
to produce magnesium oxide. Ask students to explain how mass is conserved
in this reaction. (The difference between
the mass of the magnesium and the mass
of the magnesium oxide is the mass of the
oxygen with which magnesium combines.)
2.4 Section Assessment
28.
Figure 2.15 Explain that the photos are
before and after views of a reaction. Ask,
Why are the containers covered? (The
covers prevent evaporation of the solutions and loss of mass.)
34. Hydrogen and oxygen react chemically to form
water. How much water would form if 4.8 grams
of hydrogen reacted with 38.4 grams of oxygen?
The Scientific Method Lavoisier proposed the law
of conservation of mass in 1789. Write a paragraph
describing, in general, what Lavoisier must have
done before he proposed this law. Use what you
learned about the scientific method in Section 1.3.
Connecting
Concepts
Lavoisier would have done a series of
experiments in which he measured
the masses of reactants and products
before he proposed the law of conservation of mass.
32. Classify the following changes as physical or
chemical changes.
a. Water boils.
c. Milk turns sour.
b. Salt dissolves in water.
d. A metal rusts.
33. According to the law of conservation of mass,
when is mass conserved?
Assessment 2.4 Test yourself
on the concepts in Section 2.4.
with ChemASAP
Section 2.4 Chemical Reactions 55
If your class subscribes to the
interactive Textbook, use it to
review key concepts in Section 2.4.
with ChemASAP
Section 2.4 Assessment
28. The composition of matter always
changes during a chemical change.
29. a transfer of energy, a change in color, the
production of a gas, the formation of a
precipitate
30. The mass of the products is always equal
to the mass of the reactants.
31. In a physical change, the chemical composition of a substance does not change.
In a chemical change, the chemical composition of the reactants changes as one
or more products form.
32. a. physical
b. physical
c. chemical
d. chemical
33. Mass is conserved in every physical
change or chemical reaction.
34. 43.2 g
Answers to...
Figure 2.15 change of color and
formation of a precipitate; The balance reading did not change.
Checkpoint
The burning of
methane produces heat that is
transferred to the food.
Matter and Change
55
Small-Scale
LAB
Small-Scale
LAB
1 2 3 Black!
L2
Objective In this activity, students will
begin to:
• familiarize themselves with smallscale equipment and methodology.
• observe and analyze some chemical
reactions.
Skills Focus Observing, Classifying
Purpose
Prep Time 1 hour
Materials Paper, metric ruler, reaction
surface, pipette, dropper, spatulas, KI,
liquid starch, cereal, NaClO, H2O2,
CuSO4, foods, iodized and non-iodized
salt, antacid tablets, color marker pens
Advance Prep
Procedure
1 + 2 + 3 = Black!
Solution
0.1M KI
Preparation
4.2 g KI in 250 mL water
To make macroscopic observations of chemical
reactions and use them to solve problems.
Materials
• paper
• metric ruler
• reaction surface
• materials shown in grid
• pipette, medicine droppers, and spatulas
1. Draw two copies of the grid on separate sheets
of paper. Make each square in the grid 2 cm on
each side.
2. Place a reaction surface over one of the grids.
Use the second grid as a data table to record
your observations.
3. Use the column and row labels to determine which
materials belong in each square. Depending on the
material, add one drop, one piece, or a few grains.
4. Stir each mixture by forcing air from an empty
pipette as directed by your teacher.
0.2M CuSO4 12.5 g CuSO4•5H2O in
250 mL water
1% NaClO
3% H2O2
NaClO
H2O2
CuSO4
Analyze and Conclude
Using your experimental data, record the answers to the
following questions below your data table.
1. What color is a mixture of sodium hypochlorite (NaClO)
and potassium iodide (KI)?
2. What happens when you mix NaClO, KI, and starch?
3. What do NaClO, H2O2, and CuSO4 have in common?
4. What substance is found in both paper and cereal?
How do you know?
5. If you used NaClO instead of CuSO4 in reactions other
than the reaction with KI and starch, would you expect
the results to always be identical? Explain your answer.
You’re The Chemist
50 mL household bleach
in 200 mL water
Use undiluted household hydrogen peroxide
20% starch 50 mL liquid starch in
200 mL water
KI
KI ⴙ
Starch
KI ⴙ
Paper
Class Time 40 minutes
Teaching Tips
• Demonstrate how to use a pipette as a
stirrer. This information, as well as a discussion of reaction surfaces, can be
found in the Small-Scale Chemistry
Laboratory Manual.
• Explain that using a mixture of KI and
NaClO to test for starch is an example
of qualitative analysis.
KI ⴙ
Cereal
The following small-scale activities allow you to develop
your own procedures and analyze the results.
1. Design It! Design and carry out an experiment to see
which foods contain starch.
2. Design It! Read the label on a package of iodized salt.
How much KI does iodized salt contain? Design an
experiment to demonstrate the presence of KI in
iodized salt and its absence in salt that is not iodized.
3. Design It! Antacid tablets often contain starch as a
binder to hold the ingredients in the tablet together.
Design and carry out an experiment to explore various
antacid tablets to see if they contain starch.
4. Analyze It! NaClO is a bleaching agent. Such agents
are used to whiten clothes and remove stains. Use
different color marker pens to draw several lines on a
piece of white paper. Add one drop of NaClO to each
line. What happens? Try inventing a technique that you
can use to make “bleach art.”
56 Chapter 2
Expected Outcome
NaClO
KI
H2O2
CuSO4
yellow yellow brown ppt
KI + starch black
black
black
KI + paper black
black
black
KI + cereal black
black
black
For Enrichment
L3
Have students design and carry out an
experiment to quantify the amount of KI
in iodized salt.
56 Chapter 2
Analyze and Conclude
You’re The Chemist
1. yellow
2. The mixture turns a blue-black color.
3. They all turn a mixture of KI and starch black.
4. Starch; both turn blue-black, which suggests
the presence of starch.
5. The results may be the same in reactions that
are similar to the one with KI and starch, but
different in other reactions.
1. Add KI + NaClO to various foods. A black
color indicates the presence of starch.
2. Most table salt contains 0.01% KI. Wet only a
portion of a small pile of salt with starch. Add
CuSO4 or H2O2. A black color indicates the
presence of KI.
3. If an antacid tablet contains starch, it will
turn black when treated with KI + NaClO.
4. The color fades. A picture can be drawn with
colored ink. Areas can be treated with NaClO
to bleach parts of the picture.