Section 2.1
2.1 Classifying Matter
1 FOCUS
Objectives
2.1.1
2.1.2
2.1.3
2.1.4
2.1.5
2.1.6
Classify pure substances as
elements or compounds.
Describe the characteristics of
an element and the symbols
used to identify elements.
Describe the characteristics of
a compound.
Distinguish pure substances
from mixtures.
Classify mixtures as heterogeneous or homogeneous.
Classify mixtures as solutions,
suspensions, or colloids.
Key Concepts
Why are elements and
compounds classified as
pure substances?
How do mixtures differ
from pure substances?
What is the main
difference among
solutions, suspensions,
and colloids?
Vocabulary
◆
◆
◆
◆
◆
◆
◆
◆
◆
pure substance
element
atom
compound
heterogeneous
mixture
homogeneous
mixture
solution
suspension
colloid
Reading Strategy
Summarizing Copy the diagram below. As
you read, complete the classification of matter.
Matter
a. ?
Element
Mixture
b. ?
c. ?
d. ?
E
ach piece of clothing sold has a care label, which lists recommended
cleaning methods for the clothing. For a sweater, the instructions
might say to machine wash the sweater using a gentle cycle, and then
tumble dry at a low temperature. They might say to hand wash the
sweater in cold water and lay the sweater flat to dry. The label might
even say, “Dry clean only.”
Why is it necessary to put care instructions on a label? The same
cleaning method will not work for all materials. For example, a shirt
made from 100 percent cotton may need to be ironed after washing.
But a shirt made from a cotton and polyester blend may come out of
the dryer wrinkle free. A wool jacket often needs to be dry cleaned
because wool can shrink when washed in water.
The tendency to wrinkle when washed is a property of cotton.
The tendency not to wrinkle when washed is a property of polyester. The tendency to shrink when washed is a property of wool.
Cotton, wool, and polyester have different properties because
they have different compositions. The word composition
comes from a Latin word meaning “a putting together,” or
the combining of parts into a whole. Based on their compositions, materials can be divided into pure substances
and mixtures.
Reading Focus
Build Vocabulary
L2
Paraphrasing To help students
understand the definitions of vocabulary terms, you may replace less familiar
words in a definition with a more familiar
word or phrase. For example, you can
replace distributed in the definition of a
homogeneous mixture with “spread
out,” or shattering in the definition of
malleability with “breaking into pieces.”
Reading Strategy
L2
a. Substance b. Compound
c. and d. Homogeneous mixture or
heterogeneous mixture
2 INSTRUCT
Figure 1 You can use the care labels on clothing to
sort laundry into batches for cleaning. The care
label shown is for a wool sweater that needs to be
dry cleaned or washed by hand.
L2
Some students may associate the term
material exclusively with solids because
they can see and hold solid materials.
They may have difficulty recognizing
that liquids and gases are also matter.
Challenge this misconception by pointing to the Materials list for the lab on
p. 60 and asking students to identify
the liquids.
Verbal
38 Chapter 2
38
Chapter 2
Section Resources
Print
• Guided Reading and Study Workbook
With Math Support, Section 2.1
• Transparencies, Chapter Pretest and
Section 2.1
Technology
• iText, Section 2.1
• Presentation Pro CD-ROM, Chapter Pretest
and Section 2.1
• Go Online, NSTA SciLinks, Mixtures
Pure Substances
Pure Substances
FYI
Matter that always has exactly the same composition is classified as a
pure substance, or simply a substance. Table salt and table sugar are
two examples of pure substances. Every pinch of salt tastes equally
salty. Every spoonful of sugar tastes equally sweet.
Every sample of
a given substance has the same properties because a substance has
a fixed, uniform composition. Substances can be classified into two
categories—elements and compounds.
Samples of pure substances almost
always contain impurities, some that
are unintentional, some intentional.
For example, table salt is not pure
sodium chloride. It contains between
0.006% and 0.01% potassium iodide.
Elements
Elements
Although there are millions of known substances, there are only about
100 elements. An element is a substance that cannot be broken down
into simpler substances. Imagine cutting a copper wire into smaller
and smaller pieces. Eventually you would end up with extremely tiny
particles called copper atoms. An atom is the smallest particle of an
element.
An element has a fixed composition because it contains
only one type of atom.
No two elements contain the same type of atom. In Chapter 4, you
will find out more about atoms, including how the atoms of one element differ from the atoms of every other element.
Figure 2 Aluminum, carbon, and
gold are elements that you can
see in common objects, such as
cans, pencils, and rings. Mixtures
containing iodine are used to
prevent and treat infections.
Analyzing Data Which of these
elements has a symbol that is not
related to its name in English?
FYI
Sometimes an atom is defined as “the
smallest particle of an element that has
the properties of the element.” However,
an atom of copper has none of the properties associated with bulk copper, such
as malleability, ductility, or density.
Build Science Skills
Examples of Elements At room temperature (20°C, or 68°F),
most elements are solids, including the elements aluminum and
carbon. You have seen aluminum foil used to wrap food. Most soft
drink cans are made from aluminum. Carbon is the main element in
the marks you make with a pencil on a piece of paper. Some elements
are gases at room temperature. The elements oxygen and nitrogen are
the main gases in the air you breathe. Only two elements are liquids at
room temperature, bromine and mercury, both of which are extremely
poisonous. Figure 2 shows four elements and their symbols.
Iodine (I)
L2
Observing Have students look at the
elements in Figure 2. Ask, What are
some characteristics of the elements
in Figure 2? (Gold is yellow and shiny.
Aluminum is gray and shiny. Carbon is dull
and black. Iodine is a dark purple solid.)
Follow up on their observations by asking
students to hypothesize about why the
iodine sample is in a closed container. (At
room temperature, iodine evaporates and
forms a purple gas, which is visible in the
container. The gas is poisonous.)
Visual
Aluminum (Al)
Gold (Au)
Carbon (C)
Properties of Matter 39
Customize for English Language Learners
Sharing Experiences
Encourage multilingual students to describe
what a particular element is called in their
native language. This exercise will be most
useful for those elements that have been
known for centuries or millennia. (Examples
include carbon, mercury, sulfur, iron, copper,
tin, zinc, silver, gold, and lead.) Use this
information as a springboard for discussing
the element names given in the text.
Answer to . . .
Figure 2 Gold
Properties of Matter 39
Section 2.1 (continued)
Integrate
Language Arts
Symbols for Elements In 1813, Jöns Berzelius, a Swedish
L2
Silicon
Have students research and explain the
origin of element symbols (other than
Au) that are not abbreviations for element names in English. Examples include
silver (Ag), lead (Pb), tin (Sn), antimony
(Sb), and mercury (Hg).
Verbal, Portfolio
Compounds
FYI
When the terms element, atom, compound, and molecule are defined in an
introductory section, the definition of
a molecule is often both too broad
and too narrow. Molecules are not the
smallest particle of all compounds,
and many elements exist in nature as
molecules. For this reason, in this text,
the formal definition of molecule does
not appear until Chapter 6, the chapter
on bonding, where it can be defined
accurately. (The term molecule is
introduced informally in Section 3.3
when water molecules are described.)
chemist, suggested that chemists use symbols to represent elements.
Many of the symbols he assigned to elements are still used. Each symbol
has either one or two letters. The first letter is always capitalized. If there
is a second letter, it is not capitalized.
It is easy to see why C and Al are used to represent carbon and aluminum. But why does gold have the symbol Au? The symbols that
Berzelius chose were based on the Latin names of the elements. The
Latin name for gold is aurum.
The symbols allow scientists who speak different languages to communicate without confusion. For example, nitrogen is known as azote
in France, as stickstoff in Germany, and as nitrógeno in Mexico. But scientists who speak English, French, German, and Spanish all agree that
the symbol for the element nitrogen is N.
Sometimes an element’s name contains a clue to its properties. For
example, the name hydrogen comes from the Greek words hydro and
genes, meaning “water” and “forming.”
Compounds
Oxygen
Figure 3 Elements have different
properties than their compounds.
Silicon is a gray solid and oxygen is
a colorless gas, which can be
stored in a metal tank. Silicon and
oxygen combine to form silicon
dioxide—a colorless, transparent
solid found in most grains of sand.
Silicon
dioxide
Water is composed of the elements hydrogen and oxygen. When electricity passes through water, bubbles of oxygen and hydrogen gas form
and rise to the surface of the water. If the gases are collected in a container and a flame is brought near the mixture, the hydrogen and
oxygen react and form water. Water is classified as a compound. A
compound is a substance that is made from two or more simpler substances and can be broken down into those simpler substances. The
simpler substances are either elements or other compounds.
The properties of a compound differ from those of the substances
from which it is made. For example, oxygen and hydrogen are gases at
room temperature, but water is a liquid. Hydrogen can fuel a fire, and
oxygen can keep a fire burning, but water does not burn or help other
substances to burn. In fact, water is one of the substances commonly
used to put out fires.
Figure 3 shows another example of how properties change when
elements join and form compounds. Silicon dioxide is a compound
found in most light-colored grains of sand. It is a colorless, transparent
solid. Yet, silicon dioxide is made from a colorless gas (oxygen) and a
gray solid (silicon). Silicon is used to make chips for computers.
A compound always contains two or more elements joined in
a fixed proportion. For example, in silicon dioxide, there are always two
oxygen atoms for each silicon atom. (Di- means “two.”) In water, there
are always two hydrogen atoms for each oxygen atom.
What happens if electricity passes through water?
40
Chapter 2
Facts and Figures
Electrolysis of Water Early chemists
were able to use heat to break down many
compounds into their constituent elements.
Because water cannot be decomposed by this
method, water was classified as an element
until chemists were able to use electric current
40 Chapter 2
to break down water into hydrogen and
oxygen. (The decomposition of water into
hydrogen and oxygen will not occur unless
ions are added to the water because there are
not enough ions in pure water to conduct
an electric current.)
Mixtures
Figure 4 The ingredients shown
are used to make one kind of
salsa, which is an example of a
heterogeneous mixture.
Salsa
oes
um tomat
• 4 or 5 pl
Serrano
sh
fre
5
• 3–
s
chili pepper
of cilantro
s
rig
sp
12
•
c clove
• large garli
ite onion
• small wh
1 teaspoons
•1 2
juice
fresh lime
•
teaspoon
salt
3
4
Figure 5 Sand is a heterogeneous mixture. The spoon
is stainless steel, which is a
homogeneous mixture.
Interpreting Photographs
Explain how viewing sand
through a hand lens helps show
that sand is a heterogeneous
mixture.
L1
Compare and Contrast Refer to
page 226D in Chapter 8, which provides the guidelines for comparing
and contrasting.
Have students read pp. 41–44 and gather
information on different classifications of
mixtures. Then, have students create a
chart that compares and contrasts each
type of mixture.
Visual
Integrating
Language Arts
Mixtures
Suppose you are making salsa using the ingredients shown in Figure 4.
You have a choice. You can use exactly the amounts listed in the recipe,
or you can adjust the ingredients according to your own taste. You
might have to prepare the recipe a few times before deciding if you
have just the right amount of each ingredient.
Mixtures tend to retain some of the properties of their individual
substances. But the properties of a mixture are less constant than the
properties of a substance.
The properties of a mixture can vary
because the composition of a mixture is not fixed. The type of pepper
and the quantity of pepper used in a salsa recipe determine the “hotness” of a batch of salsa. Chili peppers contain a compound called
capsaicin (kap SAY uh sin) that can cause a burning sensation in your
mouth. The amount of capsaicin varies among types of peppers.
Cayenne peppers, for example, contain more capsaicin than do
jalapeño peppers.
No matter how well you stir a batch of salsa, the ingredients
will not be evenly distributed. There may, for example, be
more onion in one portion of the salsa than another.
Mixtures can be classified by how well the parts of the mixture are distributed throughout the mixture.
Build Reading Literacy
L2
Have students consider the difference
between hot food (as in warm versus
cold) and hot food (as in spicy versus
mild). Encourage students to suggest
examples of dishes other than salsa
that are hot in the second, spicy sense.
Some students may want to record a
family recipe for a “hot” dish. Have
them identify the ingredient(s) that
can be varied to control the “hotness”
of the mixture.
Logical
Build Science Skills
L2
Observing Have students look at
samples of sand with a hand lens. Explain
that the composition of sand can vary
from beach to beach because the rocks
and shells from which sand forms have
different compositions. Ask, How can
you tell that sand is a heterogeneous
mixture? (The grains of sand vary in color
and size.) (A sample of sand that contains
only ground-up shells would probably be
classified as homogeneous.)
Visual
Heterogeneous Mixtures If you look at a handful
of sand from a beach, the sand appears to be all the same
material. However, if you use a hand lens, you will notice that the
sample of sand is not the same throughout. Figure 5 shows that grains
of sand vary in size. Also, some grains are light in color and some are
dark. Sand is an example of a heterogeneous mixture. Heterogeneous
(het uh roh GEE nee us) comes from the Greek words hetero and genus,
meaning “different” and “kind.” In a heterogeneous mixture, the parts
of the mixture are noticeably different from one another.
Properties of Matter 41
Facts and Figures
Capsaicinoid Content Capsaicin (8-methylN-vanillyl-6-nonenamide) is the most abundant
of a group of compounds called capsaicinoids.
These compounds are found in the seeds and
membranes of chili peppers. When they are
ingested, they affect pain receptors in the
mouth and throat. Because capsaicin is an oil,
and oil and water do not mix, drinking water
spreads the oil to more parts of the mouth
and increases the burning sensation.
The capsaicinoid content of a pepper is
measured in Scoville units. Wilbur Scoville
developed the method for measuring the
“hotness” of chili peppers in 1912. He mixed
ground chilies with a sugar and water solution
and diluted the mixture until tasters no longer
reported a burning sensation. The greater the
dilution needed, the higher the assigned
number of Scoville units. Fifteen Scoville units
is equivalent to one part per million.
Answer to . . .
Figure 5 More details are visible
in the magnified sand, making it
easier to observe the different parts
of the mixture.
Bubbles of oxygen and
hydrogen form and rise
to the surface of the water.
Properties of Matter 41
Section 2.1 (continued)
Do the Contents of Two
Cans of Mixed Nuts
Meet FDA Regulations?
Contents of Two Cans of Mixed Nuts
Do the Contents of Two Cans
of Mixed Nuts Meet FDA
Regulations?
L2
Answers
1. Both brands contain the same six
types of nuts, but the amount of each
type of nut varies.
2. There are 344.79 g in Brand A and
350.32 g in Brand B. The percents by
mass in Brand A are: 44.2% peanuts,
13.64% almonds, 16.79% Brazil nuts,
13.4% cashews, 5.77% hazelnuts,
and 6.21% pecans. The percents by
mass in Brand B are: 54.8% peanuts,
8.90% almonds, 5.59% Brazil nuts,
21.06% cashews, 4.82% hazelnuts, and
4.82% pecans.
3. Yes. Both brands contain more than
four types of nuts other than peanuts.
The percent of each nut by mass is within
the 2% to 80% range.
4. The ingredients are listed in order by
total mass. The ingredient with the
largest total mass is listed first.
For Extra Help
The Food and Drug Administration (FDA) has two
main areas of concern about food. First, and most
important, the FDA ensures that food sold in the
United States is safe to eat. Second, the FDA
ensures that the information on a food label
accurately describes a food product.
What can you assume when you see the label
“mixed nuts” on a can of nuts? According to the
FDA regulations, a can labeled mixed nuts must
contain at least four types of shelled nuts other
than peanuts. The mass of each type of nut must
be not less than 2 percent of the total mass and
not more than 80 percent of the total mass.
Mass in
Brand A
Mass in
Brand B
Peanut
152.39 g
191.96 g
Almond
47.02 g
31.18 g
Brazil nut
57.88 g
19.60 g
Cashew
46.20 g
73.78 g
Hazelnut
19.90 g
16.90 g
Pecan
21.40 g
16.90 g
1. Comparing and Contrasting How are
the two brands of mixed nuts alike? How
are they different?
2. Calculating What is the percent by mass of
each type of nut in each can?
3. Drawing Conclusions Do the contents of
each can meet the FDA regulations? Explain.
4. Inferring On the Brand A label, the nuts
are listed in this order: peanuts, Brazil nuts,
almonds, cashews, pecans, and hazelnuts.
What do you think determines the order?
Homogeneous Mixtures If you collect water from both the
shallow end and the deep end of a swimming pool, the water samples
will appear the same. The water in a swimming pool is a homogeneous
(hoh moh GEE nee us) mixture of water and substances that dissolve in
water. In a homogeneous mixture, the substances are so evenly distributed that it is difficult to distinguish one substance in the mixture
from another. A homogeneous mixture appears to contain only one
substance. The serving spoon in Figure 5 is made of stainless steel—a
homogeneous mixture of iron, chromium, and nickel.
L1
Have students answer Question 3 by calculating 2% and 80% of each total mass
and checking to see if any of the masses
fall outside that range.
Logical
Solutions, Suspensions, and Colloids
It isn’t always easy to tell a homogeneous mixture from a heterogeneous
mixture. You may need to observe the properties of a mixture before you
decide. The size of the particles in a mixture has an effect on the properties of the mixture.
Based on the size of its largest particles, a
mixture can be classified as a solution, a suspension, or a colloid.
Solutions, Suspensions,
and Colloids
FYI
Many alloys are not true solutions.
Sterling silver, a mixture of silver and
copper, is an example. Silver and copper
are completely soluble in all proportions
when molten. However, solid sterling
silver is a two-phase alloy with pockets
of almost pure silver and pockets of a
71.9% and 28.1% copper mixture.
Type of Nut
For: Links on mixtures
Visit: www.SciLinks.org
Web Code: ccn-1021
Solutions If you place a spoonful of sugar in a glass of hot water
and stir, the sugar dissolves in the water. The result is a homogeneous
mixture of sugar and water. When substances dissolve and form a
homogeneous mixture, the mixture that forms is called a solution.
The windshield wiper fluid in Figure 6 is a solution. So is tap water.
42 Chapter 2
Facts and Figures
Download a worksheet on
mixtures for students to complete,
and find additional teacher support
from NSTA SciLinks.
42 Chapter 2
Regulatory Agencies Responsibility for
protecting the food supply is shared among
the FDA, the Department of Agriculture, and
the EPA, which regulates pesticides. Food
that is adulterated or mislabeled may be
voluntarily destroyed or recalled, or seized
by court order. The FDA is responsible for
establishing standards for identity, quality,
and fill of container. If standards have been
set for a product, such as mixed nuts, the
product must comply with those standards.
Food labels must include a statement of
identity (usual or common name), the net
quantity of the contents, the name and
place of business of the supplier, and a
list of ingredients in descending order by
mass. The goal is to have honest and
informative labels.
A
Figure 6 The liquids shown represent
three categories of mixtures. A Windshield
wiper fluid is a solution. B Muddy water
collected from a swamp is a suspension.
C Milk is a colloid.
Comparing and Contrasting Based on
appearance, how are a solution and a
colloid similar?
Transmission Versus
Scattering
L2
Purpose Students observe light pass
through different mixtures.
B
C
Materials 2 beakers, water, iodine
solution, table salt, stirring rods, milk,
fish tank, flashlight, white paper
Procedure Demonstrate that a
solution can have color and still transmit
light. Fill two beakers halfway with
water. Add a small amount of iodine
solution to one beaker and stir. Add
table salt to the second beaker. Ask
students to describe the color of each
mixture and state whether it is clear.
Demonstrate transmission of light versus
scattering. Fill the tank with water. Turn
off the lights. Shine a flashlight through
the tank so that it lights up the white
paper placed behind the tank. Add
some milk to the water and stir. Shine
the light through the tank again. (These
behaviors of light are discussed in detail
in Section 18.3.)
Liquid solutions are easy to recognize. They do not separate into
distinct layers over time. If you pour a liquid solution through a filter,
none of the substances in the solution are trapped in the filter. You can
see through solutions that are liquids because light passes through
them without being scattered in all directions. These three properties
of liquid solutions can be traced to the size of the particles in a solution. The particles in a solution are too small to settle out of the
solution, be trapped by a filter, or scatter light.
Suspensions Have you ever seen the instruction “Shake well
before using” on a bottle? This instruction is a clue that the material in
the bottle is a suspension. A suspension is a heterogeneous mixture
that separates into layers over time. For example, if you shake up a container of sand and water, the sand mixes with the water and forms a
suspension. Over time, the suspended particles of sand settle to the
bottom of the container.
You could use a filter to separate the sand from the water. The water
would pass through the filter, but the sand would remain in the filter
paper. Suspended particles settle out of a mixture or are trapped by a
filter because they are larger than the particles in a solution. The
worker in Figure 7 is using a mask to filter out particles of plastic foam
that are suspended in air. Because larger particles can scatter light in all
directions, suspensions are cloudy.
Expected Outcome Although the
salt solution is colorless and the iodine
solution is colored, both transmit light.
Light passes through the water in the
tank and makes a bright spot on the
paper. With milk added, the light is
scattered so that the spot is much
less distinct.
Visual
What happens to suspended particles over time?
Figure 7 When a surfboard is
sanded, particles of plastic
become suspended in air. The
worker wears a mask to keep
from breathing in the particles.
Properties of Matter 43
L1
Use Visuals
Figure 7 To emphasize that suspended
particles settle out over time, ask, What
will happen to the particles of plastic
suspended in the air? (The plastic particles will eventually settle out.) Discuss
with students the dangers of inhaling
suspended particles. Ask, How does a
mask prevent the worker from inhaling particles of plastic? (The particles in
suspensions can be separated by filtration.
The mask is a filter.)
Visual
Answer to . . .
Figure 6 The solution and the colloid
both appear homogeneous.
Suspended particles
settle out of a mixture.
Properties of Matter 43
Section 2.1 (continued)
Build Science Skills
L3
High beam
Classifying Have interested students
research categories of colloids such as
gels, foams, aerosols, and emulsions.
Have students find out how scientists
distinguish different types of colloids.
Have them identify household examples
of each type.
Visual, Portfolio
3 ASSESS
Evaluate
Understanding
L2
Have students make a game of concentration using the terms in the chapter
and their definitions. Have groups of
students write each term on separate
index cards and the definition of each
term on a second set of index cards. To
play the game, students should shuffle
all the cards together and then lay them
face down in a grid. Each student takes
turns flipping over two index cards. If
the cards match, the student can remove
the cards from the grid. If the cards do
not match, the student places the cards
face down. After all of the cards are
gone, the student who has removed
the most cards wins the match.
Reteach
Low beam
Colloids Milk is a mixture of substances including water, sugar, pro-
Figure 8 The photograph shows
how water droplets in fog scatter
the light from high beams. The
drawing compares the areas lit by
high beams and low beams.
Interpreting Diagrams Which
beams normally make a larger
area of a road visible?
teins, and fats. When fresh cow’s milk is allowed to stand, a layer of
cream rises to the top. This layer contains much of the fat in the milk.
In the milk you buy at the store, the cream does not form a separate layer.
The milk has been processed so that the fat remains dispersed throughout the milk. The result is homogenized milk, which is a colloid.
A colloid contains some particles that are intermediate in size
between the small particles in a solution and the larger particles in a
suspension. Like solutions, colloids do not separate into layers. You
cannot use a filter to separate the parts of a colloid.
Fog is a colloid of water droplets in air. Figure 8 shows how fog
affects which headlights a driver uses. Automobiles have headlights
with low beams for normal driving conditions and high beams for
roads that are poorly lit. With the high beams, a driver can see a bend
in the road or an obstacle sooner. But the high beams are not useful on
a foggy night because the water droplets scatter light back toward the
driver and reduce visibility. With the low beams, much less light is scattered. The scattering of light is a property that can be used to
distinguish colloids and suspensions from solutions.
Section 2.1 Assessment
Reviewing Concepts
L1
1.
Use Figure 6 as a visual aid to summarize
the key differences among different
types of mixtures.
2.
3.
4.
5.
Students should specify which
ingredients are required for the cereal to
qualify for a particular label and suggest
a range for ingredients such as dried
fruit or nuts. (Students could choose
another edible mixture, such as canned
vegetable soup.)
Why does every sample of a given
substance have the same properties?
Explain why the composition of an
element is fixed.
Describe the composition of a compound.
Why can the properties of a mixture vary?
On what basis can mixtures be classified
as solutions, suspensions, or colloids?
Critical Thinking
6. Predicting If you added salt instead of sugar
to a pitcher of lemonade, how would this
change the properties of the lemonade?
44
7. Interpreting Visuals Explain why silicon
dioxide cannot be the only compound in the
sample of sand shown in Figure 5.
8. Inferring Fresh milk is a suspension. After
fresh milk is homogenized, it is a colloid. What
happens to the size of the drops of fat in milk
when milk is homogenized?
Writing Instructions Pick a cereal that is
an obvious mixture. Write rules that could be
used to control the cereal’s composition. Use
the FDA rules for mixed nuts as a model.
Chapter 2
If your class subscribes to
iText, use it to review key concepts in
Section 2.1.
Section 2.1
Answer to . . .
Figure 8 High beams
44 Chapter 2
Assessment
1. A pure substance has a fixed composition.
2. An element contains only one kind of atom.
3. Compounds contain two or more elements
joined in a fixed proportion.
4. Because the composition of a mixture is
not fixed
5. Mixtures can be classified as solutions,
suspensions, or colloids based on the size
of their largest particles.
6. The lemonade would taste salty instead
of sweet.
7. Silicon dioxide is colorless. There must be at
least one other compound in the sample to
account for the dark-colored grains.
8. Large drops are broken down into smaller
drops, which can remain dispersed
throughout the milk.
Section 2.2
2.2 Physical Properties
1 FOCUS
Objectives
Key Concepts
Vocabulary
What are some examples
of physical properties?
◆
How can knowing the
physical properties of
matter be useful?
◆
What processes are used
to separate mixtures?
When does a physical
change occur?
◆
◆
◆
◆
◆
◆
◆
physical property
viscosity
conductivity
malleability
melting point
boiling point
filtration
distillation
physical change
Reading Strategy
2.2.1
Building Vocabulary Copy the table. As
you read, write a definition for each property.
Physical Property
Definition
Viscosity
a.
?
Malleability
b.
?
Melting point
c.
?
2.2.3
2.2.4
2.2.5
I
f there are pitchers of ice water and lemonade on a picnic table, how
do you know which liquid is in each pitcher? It’s easy! The lemonade
is yellow. Lemonade also has a tart taste that is hard to miss. A yellow
color and a tart taste are two properties of lemonade.
Examples of Physical Properties
A physical property is any characteristic of a material that can be
observed or measured without changing the composition of the substances in the material.
Viscosity, conductivity, malleability,
hardness, melting point, boiling point, and density are examples
of physical properties.
Reading Focus
Build Vocabulary
Figure 9 The object in the
photograph is called a honey
dipper. Honey is an example of a
liquid with a high viscosity.
Viscosity Suppose you knock over an open bottle of vinegar and
an open jar of honey at exactly the same time. In the time it takes for
the vinegar bottle to empty, the honey will scarcely start to flow. The
tendency of a liquid to keep from flowing—its resistance to flowing—
is called its viscosity. The greater the viscosity, the slower the liquid
moves. Thick liquids, such as corn syrup and the honey in Figure 9, have
a high viscosity. Thin liquids, such as vinegar, have a low viscosity.
The viscosity of a liquid usually decreases when it is heated. For
example, a spoonful of cooking oil will spread more quickly across the
bottom of a heated frying pan than across the bottom of a cold pan.
Why is the viscosity of a liquid important? Consider the motor oil
used to keep the parts of an automobile engine from wearing away as
they move past one another. The motor oil must not be too thick in cold
weather or too thin in hot weather.
L2
LINCS Have students use the LINCS
strategy to learn and review the terms
viscosity, conductivity, and malleability. In
LINCS exercises, the students List what
they know about each term, Imagine a
picture that describes the word or phrase,
Note a reminding “sound-alike” word
(such as visible, train conductor, and
mallet), Connect the terms to the soundalike word by making up a short story,
and then perform a brief Self-test.
Reading Strategy
L2
a. The tendency of a liquid to resist
flowing b. The ability of a solid to be
hammered without shattering c. The
temperature at which a substance
changes from a solid to liquid
2 INSTRUCT
Examples of
Physical Properties
Properties of Matter 45
Section Resources
Print
• Laboratory Manual, Investigation 2B
• Guided Reading and Study Workbook
With Math Support, Section 2.2 and
Math Skill: Melting and Boiling Points
• Transparencies, Section 2.2
2.2.2
Describe physical properties of
matter.
Identify substances based on
their physical properties.
Describe how properties are
used to choose materials.
Describe methods used to
separate mixtures.
Describe evidence that
indicates a physical change is
taking place.
Technology
• iText, Section 2.2
• Presentation Pro CD-ROM, Section 2.2
• Go Online, Science News, Properties of
matter
FYI
The text mentions that lemonade can
be identified by its taste. Remind students that taste should never be used to
identify an unknown substance and that
no substances, known or unknown,
should ever be ingested in a lab.
Properties of Matter 45
Section 2.2 (continued)
Liquid crystal
thermometer
Metal rod
Wooden rod
Comparing Heat Conductors
Foam cups
Comparing Heat
Conductors
Materials
L2
2 plastic foam cups, scissors, metric ruler, metal
rod, wooden rod, 2 liquid crystal thermometers,
hot water, clock or watch with second hand
Objective
After completing this activity, students
will be able to
• distinguish a material that is a good
conductor of heat from a material that
is a poor conductor of heat.
Procedure
1. Make a data table with a column for time and a
column to record the temperature of each rod.
2. Cut 3 cm off the top of one cup. Turn the cup
upside down. Use the metal rod to make two
holes about 3 cm apart in the bottom.
Skills Focus Observing, Inferring
Prep Time 10 minutes
3. Attach a thermometer to each rod as shown.
4. Insert both rods so they will just touch the
bottom of the second cup. Lay the cup with
the rods on the table. Do not touch the rods
and thermometers during the experiment.
Advance Prep Acquire wood and
metal rods of similar length from the
metal or woodworking classroom, a
crafts shop, or a home repair shop.
Liquid crystal thermometers may be
purchased at a pet or aquarium supply
store. You may want to cut the cups and
attach the thermometers to the rods in
advance to save class time. Thermometers can be attached to the rods with
their own adhesive backing or taped on.
Heat enough water to fill each foam cup
about 3/4 full.
5. Ask your teacher to add hot water to the
intact cup until it is about three fourths full.
Class Time 20 minutes
Safety Remind students to handle the
setup carefully to prevent burns after the
hot water is added.
Teaching Tips
• You may need to provide tape to
attach thermometers to the rods.
• Construct a blank data table on the
board, an overhead transparency,
or a computer and have each group
enter its data in this table. All data
can then be pooled and averaged
for greater accuracy.
Figure 10 Because gold is both
malleable and beautiful, it is
often used to make jewelry. These
ancient gold medallions were
made to form a necklace.
6. Hold the cup with the hot water firmly as you
place the cup with the rods on top of it.
CAUTION Be careful not to overturn the cup.
7. Observe and record the temperatures every
minute for five minutes.
Analyze and Conclude
1. Comparing and Contrasting Is metal or
wood a better conductor of heat? Explain.
2. Applying Concepts Is a metal cup a good
container for keeping a drink hot for as long as
possible? Give a reason for your answer.
3. Evaluating Describe any variables, other
than the type of material, that were not
controlled in this lab.
Conductivity Which spoon should you choose for stirring a pot
of soup heating on the stove—a metal spoon or a wooden spoon? If
one end of a metal object is heated, the other end will soon feel hot. A
material’s ability to allow heat to flow is called conductivity.
Materials that have a high conductivity, such as metals, are called
conductors. If a material is a good conductor of heat, it is usually also
a good conductor of electricity. Wood is not a good conductor of heat.
You can stir hot soup with a wooden spoon without worrying about
burning your hand because the wooden spoon stays cool to the touch.
Malleability The ancient gold objects in Figure 10 were found in
a tomb in Greece. A goldsmith made the medallions by tapping gold
with a small hammer and punch. Gold can be shaped in this way
because it is malleable. Malleability (mal ee uh BIL uh tee) is the ability
of a solid to be hammered without shattering. Most metals are malleable. By contrast, an ice cube breaks into small pieces when struck
with a hammer. So does ordinary glass when hit by a fast-moving object
such as a baseball. Solids that shatter when struck are brittle.
Why would a cook use a wooden spoon to stir
hot soup?
Expected Outcome Metal will
conduct heat faster than wood.
Analyze and Conclude
1. Metal is a better conductor. Students
should cite the differences in temperature
over time as evidence.
2. Metal is not the best choice for this
purpose. Because metals are good conductors, the contents of the cup will
cool quickly as heat is transferred to
the surroundings.
3. Depending on what rods are used,
possible sources of error are different
lengths, different diameters, and
different densities of the materials.
Kinesthetic, Logical
46 Chapter 2
46
Chapter 2
Customize for Inclusion Students
Visually Impaired
Provide students who have visual impairments
with samples of two different nontoxic solids
that have approximately the same mass. By
handling the samples, students can infer their
relative densities from their volumes.
Provide samples of materials with a range
of hardness. Have students do scratch tests
to determine an order of hardness. Students
should be able to feel any indentations on the
surfaces of the softer materials.
see which of the materials can scratch the other. The blade of a typical
kitchen knife, for example, can scratch a copper sheet because stainless
steel is harder than copper. The stainless steel in a knife blade is a hard
solid that can be shaped into a sharp cutting edge. The material used
to sharpen the blade must be harder than stainless steel. Diamond is
the hardest known material. Some of the grinding wheels used to
sharpen steel contain small grains of diamond. The man in Figure 11
is carving a canoe from a soft wood—Western red cedar.
Melting and Boiling Points If you leave a tray of ice cubes
on your kitchen counter, the ice cubes will melt. The temperature at
which a substance changes from solid to liquid is its melting point.
For water, this change normally occurs at 0°C. If you heat water to cook
pasta, the water will normally start to boil at 100°C. The temperature
at which a substance boils is its boiling point. Figure 12 shows the
melting point and the boiling point for some substances.
Figure 11 This Tlingit carver is
using an adze to carve a canoe
from Western red cedar. Red
cedar is a relatively soft wood.
Melting and Boiling Points of Some Substances
Boiling Point
Hydrogen
ⴚ259.3ⴗC
ⴚ252.9ⴗC
Nitrogen
ⴚ210.0ⴗC
ⴚ195.8ⴗC
Ammonia
ⴚ77.7ⴗC
ⴚ33.3ⴗC
Octane (found in gasoline)
ⴚ56.8ⴗC
125.6ⴗC
0.0ⴗC
100.0ⴗC
16.6ⴗC
117.9ⴗC
Water
Acetic acid (found in vinegar)
Table salt
Gold
800.7ⴗC
1465ⴗC
1064.2ⴗC
2856ⴗC
L2
There are different scales for describing
hardness. The Brinell and Rockwell scales
are based on the indentation made by an
object. The Brinell hardness number is
based on indentation depth. The Rockwell
hardness number is based on indentation
area. On a scale that measures resistance
to abrasion, only two substances are rated
above 10: cubic boron nitride (cBN), 19,
and diamond, 42.5. Have students find
out about hardness scales and describe
how they are used to characterize rocks
and minerals.
Logical, Portfolio
that density is the ratio of the mass of a substance to its volume. At
room temperature, silver has a density of 10.5 g/cm3. If a coin has a
density of 9.9 g/cm3 at room temperature, either the coin is not made
from silver or the coin contains substances in addition to silver.
Density can be used to test the purity of methanol. Methanol is a
fuel burned in some racing motorcycles. The American Motorcycle
Association (AMA) requires racers to use fuel that is at least 99.65 percent pure. Race officials may collect a sample of fuel and measure its
temperature and density. Then they compare the measured density to
the expected density of methanol at that temperature. These spot
checks keep racers from adding substances to the fuel that will give
them an unfair advantage in a race.
Melting Point
Figure 10 Gold is the most malleable
metal. Ancient Greek jewelry was often
hammered to a thickness of 0.1 to
0.15 mm. Ask, What properties of
gold can you identify from Figure 10?
(Gold is a shiny, yellow solid that can be
shaped into small, detailed pieces.) The
medallions shown in Figure 10 were
found in the Lazlo region of central Italy
and were likely made between the eighth
and sixth centuries B.C. Ask, Given the
age of this jewelry, what other property could you say gold exhibits?
(Gold is durable.)
Visual
Integrate Earth Science
Density Density can be used to test the purity of a substance. Recall
Substance
L1
Use Visuals
Hardness One way to compare the hardness of two materials is to
FYI
Boiling points depend on both
temperature and pressure. In Chapter 3,
students will study the effect of pressure
on boiling points.
Figure 12 The table lists the
melting points and boiling points
for several substances.
Analyzing Data Which of these
substances are liquids at room
temperature (20oC, or 68oF)?
Properties of Matter 47
Facts and Figures
Specific Gravity The AMA race officials
described in the text are using a hygrometer
to test specific gravity. Specific gravity is the
ratio of the mass of a solid or liquid to the
mass of an equal volume of distilled water
at 4°C. Because specific gravity is a ratio of
values that have identical units, it does not
have units. (Density is discussed in greater
detail in Chapter 1.)
Answer to . . .
Figure 12 Octane, water, and
acetic acid
A wooden spoon is a
poor conductor of heat.
Properties of Matter 47
Section 2.2 (continued)
Using Physical Properties
Using Physical
Properties
People use data about physical properties to solve many different types
of problems.
Physical properties are used to identify a material, to
choose a material for a specific purpose, or to separate the substances
in a mixture.
Build Reading Literacy
L1
Outline Refer to page 156D in
Chapter 6, which provides the
guidelines for an outline.
Using Properties to Identify Materials The steps used to
identify a material are similar to the steps used to test for purity. The
first step is to decide which properties to test. The second step is to do
tests on a sample of the unknown. The final step is to compare the
results with the data reported for known materials.
The identification of a material can be a crucial step in solving a
crime. A detective collects red paint chips from the scene of a hit-andrun accident. He asks a chemist at the crime lab to use the chips to
identify the model of the missing vehicle. Because paint is a mixture of
substances, the chemist can do tests that distinguish one type of red
paint from another. The technician compares the data she collects to
an FBI database. The database contains information about the paints
used on different makes and models of cars. Once the detective knows
the make and model, he uses a database of registered owners to create
a list of possible suspects.
Have students read pp. 48–50 and
gather information on identifying,
choosing, and separating substances
based on their physical properties. Then,
have students use the headings as major
divisions in an outline. Have students
refer to their outlines when answering
the questions in the Section 2.2
Assessment.
Visual
Using Properties to Choose Materials Properties deter-
Comparing
Melting Points
L2
Purpose Students observe the
differences in melting points of two
substances.
Materials water, ethanol, foam cups,
freezer, large beaker, thermometer
Procedure Tell students that you will
demonstrate that the melting points of
two substances differ. The night before,
place a foam cup filled with water and a
second foam cup filled with ethanol in
the freezer. During class, pull both cups
out of the freezer. Have students note
that the water is frozen, but the ethanol
is not. Remove the ice from the cup and
add it to the large beaker. Add a small
amount of water and allow the ice to
begin melting. While the temperature
of the ice water is leveling off, have a
volunteer measure the temperature of
the ethanol. Compare that temperature
to the temperature of the ice water.
Expected Outcome Because most
freezers do not cool to temperatures
below the melting point of ethanol,
–114.7°C, the ethanol will remain a
liquid. After some of the ice has melted,
the temperature of the solid-liquid
system will stop decreasing and level
off. This is the melting point of water,
0°C. The temperature of the chilled
ethanol is below 0°C.
Visual
48 Chapter 2
Figure 13 Shoelaces for hiking
boots are sometimes made from
leather. So are some belts and
shoes. Making Generalizations
What properties of leather would
make it a suitable material for all
three types of objects?
48
mine which materials are chosen for which uses. For example, you
wouldn’t want shoelaces made from wood. Shoelaces must be flexible,
that is, they must be able to bend without breaking. They must also be
durable, that is, they must be able to withstand repeated use. Laces in
hiking boots like those in Figure 13 are usually nylon or leather.
People don’t consider just one property when choosing a material for
a particular application. They look at a set of properties. For example,
the How It Works box on page 49 explains how the properties of wax
are used when clay molds are made for casting metal sculptures.
Chapter 2
Facts and Figures
Identifying Substances Sometimes a single
property is not sufficient to positively identify a
substance. Iron, nickel, and cobalt, which are
often found together in nature, look quite
similar. The density of iron is 7.87 g/cm3. The
density of nickel is 8.90 g/cm3. The density of
cobalt is 8.86 g/cm3. Measurements of mass
made on the type of balance found in most
school labs would be precise enough
to distinguish iron from cobalt or nickel, but
not precise enough to distinguish cobalt
from nickel.
Making a Sculpture
Making a Sculpture
A process called lost-wax casting is used to make metal
sculptures. Different stages of the process depend on
physical properties of wax, clay, and metal. Wax can be
carved and molded. Clay becomes brittle when baked at
a high temperature. When melted, most metals form
homogeneous mixtures, which can be poured into molds.
Interpreting Diagrams Why is it important that wax
has a low melting point?
Wax model A wax model of
the sculpture is built up around
a clay core. Wax is used because it is
soft enough for carving fine details,
but hard enough to retain its shape
at room temperature.
Wax model
Preparing clay molds
This artist from Nepal in southern
Asia is preparing molds for lost-wax
casting. She is applying layers of clay
to a wax model.
Cast metal
sculpture
Molten metal
poured into
mold
Clay core
Clay mold
Clay is applied to
the wax model in layers
of increasing coarseness,
and left to dry. The inner,
finer layers capture every
detail of the sculpture in
a smooth mold. The
outer, coarser layers
(clay mixed with sand)
provide strength.
There are a number of variations to
the method described in the text. For
example, sometimes there is no clay
core. The lost-wax method of casting
can also be used to make replicas of
existing sculptures.
Many other molding and casting
techniques also take advantage of
the physical properties of different
substances to maximize the quality
of the final product. For example, the
properties of some types of rubber make
them ideal materials for molds. Rubber
molds are flexible enough that the cast
can be pulled out without breaking the
mold, yet strong enough to preserve
fine details in the final product. Because
of their durability, rubber molds can be
reused many times.
Interpreting Diagrams The wax
must melt away when the model is
heated in a kiln.
Logical
Layers of clay
applied to the
wax model
Wax model
For Enrichment
Melting
wax
Melting wax
The clay-covered
wax model is then
baked in a kiln. Because
wax has a low melting
point, the wax model
melts away inside the
clay, leaving a hardened
shell mold. This clay
mold is then used to
make the final sculpture.
Molten metal
Molten (liquid)
metal is poured into the
clay mold and left to
cool and harden. For this
sculpture of an African
head, a mixture of
copper, zinc, and lead
was used.
L2
Broken clay
Metal sculpture
When the metal
has cooled, the clay
shell is broken open to
reveal the finished
metal sculpture.
Properties of Matter 49
L3
Because an imprint made in wet sand
will hold its shape, filling the imprint
with melted wax or wet plaster will
produce a cast of the object pressed into
the sand. This sculpting technique is
called a sand mold. Have students find
out about sand molds and use them to
make candles or plaster casts of their
footprints or handprints.
Visual, Portfolio
Use Community
Resources
L2
Arrange for a sculptor or jewelry maker
to visit the class. Have the artist describe
the molding and casting techniques
he or she uses. Before the visit, have
students prepare questions about how
the artist chooses materials based on
their physical properties.
Interpersonal
Answer to . . .
Figure 13 Flexibility and durability
Properties of Matter 49
Section 2.2 (continued)
Using Properties to
Separate Mixtures
Build Science Skills
L2
Applying Concepts
Purpose In this
activity, students use
properties to separate
the components of a mixture.
Figure 14 These Americorps
students are looking for artifacts
at the San Diego Presidio—a fort
that was built in 1769. As the
students sift dirt through a
screen, small objects buried in the
dirt collect on the screen.
Applying Concepts How could
changing the size of the holes in
a screen change the number of
objects found?
Materials a mixture of table salt, sand,
and iron filings; beaker; magnet; plastic
bag; water; funnel; filter paper
Using Properties to Separate Mixtures
Some properties can be used to separate mixtures.
distillation are two common separation methods.
Class Time 20 minutes
Procedure Encourage students to
consider properties that can be used to
separate each material from the other
two materials in the mixture. Then, have
students design a procedure to
complete the separation.
Filtration One way to make a pot of tea is to pour hot water over
loose tea leaves. Some compounds in the tea leaves, such as caffeine, dissolve in the water. You can separate the hot tea from the loose leaves by
pouring the mixture through a strainer. Using a strainer is a type of filtration. Filtration is a process that separates materials based on the size
of their particles. Particles of the compounds that dissolve are small
enough to pass through the strainer, but the tea leaves themselves are
too large to pass through the strainer. The drip method of brewing coffee
also uses a filter to separate the brewed coffee from the coffee grounds.
The students in Figure 14 are using a wire screen to locate small
objects buried in the sand at an archaeological site. Particles of dirt are
small enough to pass through the holes in the screen, but objects such
as broken bits of pottery are too large to pass through the screen.
Expected Outcome Students can
collect the iron filings using a magnet
covered with a plastic bag. They can add
water to the mixture to dissolve the salt.
They can use a filter to collect the sand.
Students can collect the salt by letting
the water evaporate for a few days.
Visual, Portfolio
L2
Students may think that all the particles
in mixtures are similar in size. This is true
for solutions and colloids, but not for
suspensions. Challenge this misconception by displaying common devices
used to filter mixtures (such as a sieve,
a colander, and a coffee filter) and
discussing the mixtures these devices
are used to separate. The size of the
holes in a filter determines whether
filtration can be used to separate a
suspension. Hole size also determines
whether all the particles in a colloid
pass through the filter or all the particles
are trapped in the filter. Either way, the
end result is that the colloid is not
separated by filtration.
Verbal
Science News provides students
with current information on
properties of matter.
50 Chapter 2
Filtration and
For: Articles on properties
of matter
Visit: PHSchool.com
Web Code: cce-1022
50
Distillation How can you separate the parts of a solution when all
the particles in a solution are small enough to pass through a filter?
Sometimes distillation can work. Distillation is a process that separates the substances in a solution based on their boiling points.
One practical use of distillation is to provide fresh water for submarines. Most submarines can store only enough fresh water to last about
ten days. Each submarine has equipment that can convert seawater into
fresh water. The water is heated until it changes from a liquid to a gas. The
gas is cooled until it changes back to a liquid, which is collected in a separate container. Boiling can separate fresh water from seawater because
water has a much lower boiling point than the compounds dissolved in
seawater. These compounds are left behind in the original container.
How can loose tea leaves be removed from a pot of
brewed tea?
Chapter 2
Facts and Figures
Tea Tea contains compounds called
polyphenols, which are often referred to as
tannins. There are health claims made for both
black and green tea. The health claims made
for green tea are related to the concentration
of polyphenols. During the processing of black
tea, most of the polyphenols are oxidized.
Oxidation of polyphenols is limited during
the processing of green tea. (The tea dumped
into Boston harbor on December 16, 1773,
was green tea, which outsold black tea in
the Colonies.)
Recognizing
Physical Changes
Recognizing Physical Changes
The change of water from a liquid to a gas during boiling is
a physical change. A physical change occurs when some of
the properties of a material change, but the substances in
the material remain the same. For example, if you slowly
heat butter in a pan, it changes from a solid to a liquid, but
the substances in the butter do not change. Two other examples of physical changes are crumpling a piece of paper and
slicing a tomato. Crumpling and slicing are actions that
change the size and shape of a material, but
not its composition.
Some physical changes can be reversed.
You can freeze water, melt the ice that forms,
and then freeze the water again. You can use
an iron to remove the wrinkles from a cotton
shirt. You can braid hair, unbraid the hair,
and then braid it again. Some physical
changes cannot be reversed. You would not
expect to reconstruct a whole tomato from
tomato slices or to replace the peel on a
peeled orange. Figure 15 shows one physical
change that can be reversed and one that
cannot be reversed.
FYI
If butter heated in a pan begins to
brown, this is a sign that a chemical
change is starting to occur. Students are
asked to compare the possible changes
to heated butter in Question 5 of the
Section 2.3 Assessment.
3 ASSESS
Figure 15 Braiding hair and
cutting hair are examples of
physical changes. Braiding is a
reversible change. Cutting cannot
be reversed.
1.
2.
3.
List seven examples of physical properties.
Describe three uses of physical properties.
Name two processes that are used to
separate mixtures.
4. When you describe a liquid as thick, are you
saying that it has a high or a low viscosity?
5. Explain why sharpening a pencil is an example
of a physical change.
6. What allows a mixture to be separated
by distillation?
Critical Thinking
7. Designing Experiments How could you
find out whether copper is harder or softer
than the plastic used in a plastic cup?
L2
Tell students that a layer of fat rises to
the top in a pot of chicken soup. Ask,
How can the cook remove the fat?
(Skim the fat from the surface or freeze
the soup and remove the solid fat layer.)
L1
Reteach
Use the How It Works feature on p. 49
to review with students the importance
of examining physical properties when
choosing a material. Discuss why the
physical properties of wax, clay, and
metal determine what roles they play in
the making of a sculpture.
Section 2.2 Assessment
Reviewing Concepts
Evaluate
Understanding
8. Inferring Why would you expect the
materials used to make pot holders to be
poor conductors of heat?
9. Applying Concepts Silicon dioxide is a
solid at room temperature and methanol
is a liquid. Which substance has the higher
melting point?
Organizing Data In what order are the
substances arranged in Figure 12? Use
what you studied about organizing data in
Section 1.4 to explain why this order is
useful. Explain why you might choose a
different order if you had similar data for
500 substances.
The substances are ordered from lowest
to highest melting point, which groups
them into gases, liquids, and solids at
room temperature. With a larger
database, alphabetical order would be
more useful for retrieving the data.
If your class subscribes to iText, use it to
review key concepts in Section 2.2.
Properties of Matter 51
Section 2.2
Assessment
1. Students may list hardness, viscosity,
conductivity, density, malleability, melting
point, and boiling point. Students may also
list color, taste, flexibility, and durability.
2. Identify materials, choose a material for a
specific purpose, or separate the substances
in a mixture
3. Filtration and distillation
4. A thick liquid has a high viscosity.
5. The shape and size of the pencil change,
but the composition of the pencil remains
the same.
6. A difference in boiling points allows
mixtures to be separated by distillation.
7. By scratching the cup with an object made
of copper
8. Pot holders are designed to prevent the
transfer of heat from a cooking utensil.
9. Silicon dioxide
Answer to . . .
Figure 14 With smaller holes, more
objects would collect on the screen.
Loose tea leaves can be
removed by filtration.
Properties of Matter 51
Getting a
Fresh Start
Getting a Fresh Start
L2
Background
Water found in nature is never 100 percent pure. There
are always substances dissolved in the water. Some of
these substances, as well as bacteria and particles of
dirt, must be removed before the water is fit to drink.
Aeration is of great importance during
waste-water treatment because of the
organic compounds in sewage. Aeration
is also important when the water source
is groundwater because of the likely
concentration of dissolved carbonates.
Water that contains dissolved calcium
and magnesium compounds is called
hard water because deposits of these
salts can accumulate in water and lessen
the effectiveness of soap. Water softeners
replace calcium and magnesium compounds with sodium compounds, which
do not cause the same problems.
Build Science Skills
1 Coarse filter A screen
■
L2
Coarse
filter
screen
Observing
Purpose Students
observe that water
can taste different
depending on its
source and on its purity.
Procedure Have students taste
samples of tap water, bottled water, and
distilled water. Have them describe any
differences or similarities they taste.
Layer of
lumps
Cleaned water
spills over into
a trough.
Mixing tank
3 Forming a colloid Alum
■
Safety Use only water that is intended
for consumption.
52 Chapter 2
2 Aeration During aeration, air
■
Colloid forms.
Alum
(aluminum
sulfate)
added
Class Time 10 minutes
Reservoir
Aeration tank
may be bubbled into the water or
water may be sprayed into the air.
Aeration removes substances from
water, such as iron compounds, that
give water an unpleasant taste.
Outlet
tower
Materials tap water, bottled water,
distilled water
Expected Outcome Students will be
able to observe that the taste that they
associate with water is due to substances
dissolved in the water, and not to the
water itself.
Kinesthetic, Visual
prevents large items such
as leaves from entering the
water treatment plant.
is added to the mixing tank.
Alum causes small particles in
the water to form a type of
colloid called a gel. Most of
the bacteria in the water are
trapped in the gel.
52
Chapter 2
4 Sedimentation In
■
the sedimentation tank,
large lumps slowly settle
to the bottom of the
tank from where they
can be removed.
Lumps
drained
off
Sedimentation tank
Going Further
Water from the ground
About half of the drinking
water in the United States
comes from natural underground sources. Although
this groundwater is filtered
as it passes through rocks
and sand, it sometimes
contains high levels of
dissolved minerals or
chemical pollutants. So
groundwater is purified
using a modified version of
surface water filtration.
6 Carbon filter The water is
■
5 Sand and gravel filter
■
Next, the water trickles
through sand and gravel
filter beds, which trap the
remaining suspended particles.
Because the filter beds can
become clogged, they are
washed every 24 hours.
sometimes passed through a
carbon filter. This filter removes
tiny amounts of dissolved
impurities, and improves the
water’s taste and color.
Water
storage
tank
Water
Fluorine softener
added
compound
added
Chlorine
added
Carbon
filter
7 Additives
■
The fluorine compound
prevents tooth decay and
the chlorine kills bacteria.
The water softener
removes some magnesium
and calcium compounds.
8 Storage Finally,
■
the water is held in
storage tanks before
passing into the
public water supply.
Most home water purification systems
use activated charcoal (AC) filters or
reverse osmosis (RO). Neither system
removes all contaminants. Activated
charcoal is an extremely porous solid
with a large surface area on which
substances are absorbed. Activated
charcoal is effective for removing volatile
organic compounds, pesticides, some
metals, and chlorine. Sometimes
bacteria grow on the filter. The surface
of the activated charcoal may become
saturated and ineffective before the
consumer replaces the filter.
During reverse osmosis, normal
household water pressure forces water
through a semipermeable membrane.
Reverse osmosis is useful for removing
lead and other transition metals,
asbestos, and many dissolved organic
compounds. Reverse osmosis is a slow,
wasteful process that uses three to nine
gallons per gallon of purified water.
(Some people use RO systems in their
fish tanks.)
In parts of the world without
municipal treatment plants, UV light is
used to kill waterborne pathogens.
Verbal
Going Further
Gravel layer
■
Some people use a system to purify water at
home. Research and write about one of these
systems. What is the system
designed to do? Compare the
method used to the processes
that occur at a water
purification plant.
■
Take a Discovery Channel Video
Field Trip by watching
“Fresh-Squeezed Water.”
Filtered water
Sand layer
Video Field Trip
Properties of Matter 53
Video Field Trip
Fresh-Squeezed Water
After students have viewed the Video Field Trip,
ask them the following questions: Why did the
people on Catalina Island need to convert
seawater to fresh water? (They were running out
of drinkable water.) What is a semipermeable
membrane? (A semipermeable membrane is a
material that has microscopic holes to allow water to
pass through while blocking salts and viruses.) What
is reverse osmosis? (During reverse osmosis, water
under high pressure passes through a semipermeable
membrane, which removes dissolved salts and other
unwanted substances.) Why is NASA also
interested in desalination methods? (Being able
to recycle the water on board a spacecraft reduces
the amount and the weight of water that must
accompany the astronauts on their voyages.)
Properties of Matter 53
Section 2.3
2.3 Chemical Properties
1 FOCUS
Objectives
2.3.1
2.3.2
2.3.3
Describe chemical properties
of matter.
Describe clues that indicate
that a chemical change is
taking place.
Distinguish chemical changes
from physical changes.
Key Concepts
Vocabulary
When can chemical
properties be observed?
◆
What observations might
indicate that a chemical
change has occurred?
◆
◆
◆
◆
chemical property
flammability
reactivity
chemical change
precipitate
What is the difference
between chemical and
physical changes?
Reading Strategy
Relating Text and Visuals Copy the table.
Find examples of the clues for recognizing
chemical changes in Figures 19 and 20.
Clue
Example
Change in color
a.
?
Production of gas
b.
?
Formation of precipitate
c.
?
Reading Focus
Build Vocabulary
L2
H
Word-Part Analysis Have students
look up the words flammable, inflammable, and nonflammable. Have them find
two meanings of the prefix in- to explain
why the terms are confusing. Ask them to
consider why it is very important to know
what each term means. (Inflammable and
flammable are synonyms. The prefix in- can
mean “not,” or “into” as in “burst into
flames.” It is important to use the correct
meanings when writing or interpreting fire
safety warnings.)
Reading Strategy
ow would you describe candles like the ones in Figure 16? You
might describe their color or their hardness. Or, you might observe
that the candles float on water, and conclude that the density of candle
wax is less than that of water. Color, hardness, and density are physical properties. But there is something else about the candles that may
seem even more obvious to you: the fact that the candles are burning.
The ability to burn is not a physical property because you cannot
observe burning without changing the composition of the material
that is burning. As a candle burns, new substances form.
Observing Chemical Properties
L2
a. Copper roof changing color from red
to green when exposed to moist air
b. Formation of carbon dioxide gas
when vinegar is added to baking soda
c. Formation of cottage cheese curds
when acid is added to milk
Figure 16 When candles burn,
new substances form. The ability
to burn is a chemical property.
2 INSTRUCT
Flammability Materials that burn can be used as fuel. Sometimes,
people use burning newspapers to start a fire in a fireplace. Gasoline is
the fuel burned in most automobiles. The chemical property that paper
and gasoline share is their flammability. Flammability is a material’s
ability to burn in the presence of oxygen.
Observing Chemical
Properties
Build Reading Literacy
L1
Preview Refer to page 36D in this
chapter, which provides the guidelines
for previewing.
Before they read the section, have
students skim the headings, visuals, and
boldfaced material to preview how the
text is organized.
Visual
FYI
If the combustion of paraffin is not
complete, carbon monoxide will form.
Combustion as a type of reaction is
addressed in Chapter 7. Combustion
of fossil fuels is discussed in Chapter 9.
54 Chapter 2
Most candles are made from paraffin, which is a mixture of compounds containing carbon and hydrogen. As a candle burns, the
compounds combine with oxygen in the air to form water and carbon
dioxide. (Carbon dioxide is the gas that gives a carbonated beverage its
fizz.) The ability to burn is a chemical property. A chemical property
is any ability to produce a change in the composition of matter.
Chemical properties can be observed only when the substances
in a sample of matter are changing into different substances.
Flammability and reactivity are two examples of chemical properties.
54
Chapter 2
Section Resources
Print
• Laboratory Manual, Investigation 2A
• Guided Reading and Study Workbook
With Math Support, Section 2.3
• Transparencies, Section 2.3
Technology
• iText, Section 2.3
• Presentation Pro CD-ROM, Section 2.3
• Go Online, NSTA SciLinks, Chemical and
physical changes
Sometimes flammability is not a desirable property. For example,
there are laws that regulate the flammability of fabrics. The fabrics used
in children’s sleepwear must have a low flammability. These fabrics are
described as flame-resistant because they are difficult to ignite. If they
do ignite, they burn slowly.
Reactivity The property that describes how readily a substance
combines chemically with other substances is reactivity. Nitrogen and
oxygen are the main gases in air. Oxygen is a highly reactive element.
Nitrogen has an extremely low reactivity.
Oxygen reacts easily with most other elements. Figure 17 shows
the rust that forms when oxygen reacts with iron and water. Rust is a
brittle, reddish-brown compound. A rusty chain or bolt is more likely
to break than a new chain or bolt because rust is weaker than iron.
Because iron is highly reactive, you would not choose iron to make
decorative objects, such as jewelry or coins.
Many uses of nitrogen depend on its low reactivity. For example,
seawater is often stored in steel tanks located below the lowest deck of
a ship. The seawater helps to keep the ship stable in the water. Over
time, rust forms in the tanks because iron in the steel reacts with
oxygen dissolved in the water. Researchers in Japan have developed a
way to reduce the amount of rust produced. They pump nitrogen gas
into the tanks, and the nitrogen displaces the dissolved oxygen.
Which element is more reactive—oxygen or nitrogen?
Oxygen Is Needed
For: Links on chemical and
physical changes
Visit: www.SciLinks.org
Web Code: ccn-1023
L2
Purpose Students observe that air is
needed for a candle to burn.
Materials 2 small candles, matches,
large beaker
Procedure Tell students that the
flammability of a material is tested in air.
Light two candles with a match. Carefully place a large beaker over one of the
candles and have students observe what
happens. Remove the beaker and relight
the candle to show that it can still burn.
Discuss how a scientist might test the
hypothesis that oxygen is the gas in air
that supports burning.
Figure 17 This automobile must
have been exposed to air and
water for many years.
Drawing Conclusions What
evidence is there that parts of the
automobile contained iron?
Expected Outcome After the beaker
is placed over the candle, the flame dies
out. The other candle continues to burn.
To demonstrate that oxygen is the gas
that supports burning, the scientist
could try burning the candle in pure
samples of the gases in air.
Visual, Logical
Build Science Skills
L2
Designing Experiments Challenge
students to describe a material that
they could test for flammability without
changing its composition. (The material
would have to be nonflammable.) Help
students by asking them how they
would test the material for flammability
and what the results of the test would
be. Explain that the absence of an
observed event is useful data.
Verbal
Properties of Matter 55
Customize for English Language Learners
Paired Brainstorming
Have students work in pairs to think of other
items—besides cars, chains, or bolts—that rust.
Examples include bicycle frames, door and
gate hinges, and old nails. Strengthen discussion skills by having students share their
examples with the class. Encourage them to
comment on what these items have in
common. Although many items made from
iron are coated with paint to prevent rusting,
paint does chip and items containing iron
will rust if left outdoors unprotected from
the elements.
Download a worksheet on
chemical and physical changes for
students to complete, and find
additional teacher support from
NSTA SciLinks.
Answer to . . .
Figure 17 The amount of rust is
evidence that much of the automobile
was made of iron.
Oxygen
Properties of Matter 55
Section 2.3 (continued)
Recognizing Chemical
Changes
Identifying a Chemical Change
Materials
4. Add 5 mL of calcium chloride solution to test
tube A. Add 5 mL of sodium chloride solution
to test tube B. Add 5 mL of copper sulfate
solution to test tube C.
3 test tubes; test-tube rack; glass-marking pencil;
3 10-mL graduated cylinders; solutions of copper
sulfate, calcium chloride, and sodium chloride
Identifying a
Chemical Change
5. Examine the test tubes for evidence of a
chemical change. Record your observations.
Procedure
L2
1. Construct a data table with columns labeled
Test Tube, Contents, and Observations.
Objective
After completing this activity, students
will be able to
• recognize evidence of a chemical
change.
2. Label the test tubes A, B, and C.
3. Pour 5 mL of copper sulfate solution into test
tube A. Pour 5 mL of calcium chloride solution
into test tube B. Pour 5 mL of sodium chloride
solution into test tube C. CAUTION Do not
allow the solutions to touch your skin. They may
cause irritation.
Skills Focus Observing, Drawing
Conclusions
Analyze and Conclude
1. Inferring In which test tube(s) did a
chemical change occur? Explain your answer.
2. Evaluating Can you be sure that a chemical
change occurred? Explain your answer.
Prep Time 20 minutes
Advance Prep To prepare 1-M
solutions of calcium chloride, sodium
chloride, and copper sulfate, dissolve
1 mole of each salt (111.0 g CaCl2;
58.5 g NaCl; or 249.69 g CuSO4•5H2O)
in approximately 800 mL of distilled or
deionized water in a 1-L volumetric
flask. Once a salt has dissolved, add
enough water to make a 1000-mL
solution. Stir the solution. Provide each
group with 25 mL of each solution in a
wash bottle, which is the easiest container for students to handle. Be sure to
label each container with its contents.
6. Pour the contents of the test tubes into the
sink. Rinse out the test tubes and flush the
contents down the drain. CAUTION Wash
your hands thoroughly with soap or detergent
before leaving the laboratory.
Recognizing Chemical Changes
Figure 18 As a banana ripens,
chemical changes cause the peel
to change color from green to
yellow. In a banana that is overly
ripe, different chemical changes
cause the peel to turn brown.
Observing Based on your
experience, what other
properties of a banana change
as it ripens?
Figure 18 shows what happens to banana peels as bananas ripen. The
color change in a banana peel is caused by chemical changes that are
taking place in the cells of the banana. A chemical change occurs when
a substance reacts and forms one or more new substances. Chemical
changes occur when a cake bakes in an oven, leaves on trees change
color, and food is digested in your stomach.
How can you recognize a chemical change? You have to look for
clues. For example, when food spoils, it often gives off an unpleasant
odor.
Three common types of evidence for a chemical change
are a change in color, the production of a gas, and the formation of
a precipitate.
Class Time 20 minutes
Safety Remind students to wash their
hands thoroughly at the end of the lab, to
be careful when handling glassware, and
to dispose properly of chemical wastes.
Teaching Tips
• Review how to pour a liquid from a
graduated cylinder and accurately
read the volume.
Expected Outcome A precipitate of
calcium sulfate will form in test tube A.
The other two combinations will show
no evidence of a chemical change.
Analyze and Conclude
1. Formation of a precipitate indicated
that a chemical change occurred in test
tube A.
2. No, formation of a precipitate is
evidence for a chemical change, but
it is not conclusive.
Visual, Logical
56 Chapter 2
56
Chapter 2
Facts and Figures
Banana Science There are four stages of
banana development: growth, maturation,
ripening, and senescence. During ripening,
bananas produce increased amounts of ethylene
gas, which triggers chemical changes. The peel
changes color and becomes more permeable,
the pulp softens, starches break down into
sugar, and compounds responsible for flavor
and aroma are produced. Once ripening begins,
the process cannot be stopped. Ripening occurs
whether the banana is attached or detached
from the parent plant.
L1
Use Visuals
A Change in Color Over time, a shiny silver bracelet that is
exposed to air will darken. As a match burns, it shrivels up and turns
black. The new copper roof and the old copper roof in Figure 19 have
different colors. In each of these examples, a change in color is a clue
that a chemical change has produced at least one new substance.
Production of a Gas Figure 20A shows what happens when
you mix vinegar with baking soda. Bubbles of carbon dioxide form
immediately. A similar chemical change happens when you use baking
powder as an ingredient in a cake recipe. Baking powder is a mixture
of baking soda and one or more acids that react when wet. As the cake
bakes, the bubbles of carbon dioxide expand and cause the cake to rise.
Figure 19 When copper is
exposed to moist air, it forms a
thin coating called a patina.
A new copper roof has a reddish
color. The green patina on an old
copper roof is a mixture of
copper compounds.
Predicting Would a patina form
faster in a rainy climate or in a
dry climate?
Figure 20 Emphasize that the best
way to determine if a chemical change
is taking place is to compare materials
before and after the reaction. Ask,
Describe baking soda and vinegar
before they are mixed. (Baking soda is a
white solid, and vinegar is a clear solution.)
What clue indicates that a chemical
change is taking place? (There is
production of a gas.) When you see no
obvious clues to a chemical change,
can you be certain that a chemical
change has not occurred? (No)
Visual
Formation of a Precipitate Another chemical change you
can observe in the kitchen is the curdling of milk. If you add lemon juice
or vinegar to milk, small bits of white solid will separate from the liquid.
Any solid that forms and separates from a liquid mixture is called a
precipitate. When an acid is added to milk, proteins in the milk undergo
a chemical change that alters their structure, causing them to stick
together in clumps. They form the precipitate shown in Figure 20B.
What happens when you add vinegar to
baking soda?
A
Figure 20 The formation of a gas or
a precipitate can be a clue to chemical
change. A Carbon dioxide gas forms
when vinegar is mixed with baking
soda. B The curds in cottage cheese
form when an acid is added to milk.
B
Properties of Matter 57
Facts and Figures
Acids in Action When acid is added to milk,
one of the proteins in milk (casein) coagulates.
The milk may thicken (as in buttermilk or
yogurt) or separate into solid curds and liquid
whey (as in cottage cheese). This process is
called curdling. Acids may be added directly to
the milk or produced by bacteria. Adding rennin
(a coagulating enzyme) produces larger curds.
Single-action baking powder contains three
dry ingredients: an acid (e.g., cream of tartar),
a base (e.g., baking soda), and filler (e.g.,
cornstarch). When water is added, the acid
and base react. Double-action baking powders
contain two acids, one that reacts faster than
the other. Recipes that use baking soda have
another ingredient that provides the acid.
Answer to . . .
Figure 18 Students may say that the
banana becomes softer and that its
odor increases.
Figure 19 In a rainy climate
Bubbles of carbon
dioxide form.
Properties of Matter 57
Section 2.3 (continued)
Figure 21 A blacksmith uses a
hammer to shape a horseshoe
that has been heated. Although
the color of the iron horseshoe
changes, no chemical change is
occurring. Inferring Other than
color, what physical property of
iron is affected by heating?
Is a Change Chemical
or Physical?
L2
Students often have trouble distinguishing chemical from physical changes.
Explain that the composition of some
substances must change during a chemical change, but the composition of all
substances must remain the same
during a physical change.
Verbal
Is a Change Chemical or Physical?
It is not always easy to distinguish a chemical change from a physical
change. Even if you observe a color change, a gas, or a precipitate, you
cannot be sure that a chemical change has taken place. When the iron
horseshoe in Figure 21 is heated, its color changes from gray to red.
Despite this change in color, the iron is still iron. When water boils on
a stove, the bubbles of gas that rise to the surface are still water.
Before you decide whether or not a chemical change has occurred,
ask yourself this question: Are different substances present after the
change takes place? If not, then the change is physical, not chemical.
When matter undergoes a chemical change, the composition of
the matter changes. When matter undergoes a physical change, the
composition of the matter remains the same.
FYI
The release of heat or light is sometimes
listed as a clue for a chemical change, but
energy changes occur with both physical
and chemical changes. Exothermic and
endothermic changes are discussed in
Sections 3.3 (Phase Changes) and 7.3
(Energy Changes in Reactions).
3 ASSESS
Evaluate
Understanding
Section 2.3 Assessment
L2
Reviewing Concepts
Have students list three clues that indicate that a chemical change is taking
place and give an example of each. Then,
have them exchange their work with a
partner and discuss examples of physical
changes that also exhibit these clues.
Reteach
1.
2.
3.
4.
L1
5.
Use Figures 18, 19, and 20 to review
the clues that indicate that a chemical
change is taking place.
Under what conditions can chemical
properties be observed?
List three common types of evidence for a
chemical change.
How do chemical changes differ from
physical changes?
Explain why the rusting of an iron bar
decreases the strength of the bar.
A pat of butter melts and then burns in a hot
frying pan. Which of these changes is physical
and which is chemical?
Critical Thinking
6. Comparing and Contrasting Compare
the properties of a raw egg to those of a
hard-boiled egg.
Students might argue that observation
and experimentation are the key steps
in a scientific method for determining
whether a change is physical or chemical.
If your class subscribes to
iText, use it to review key concepts in
Section 2.3.
Answer to . . .
Figure 21 Malleability increases.
58 Chapter 2
58
7. Classifying If you spill household bleach on
denim jeans, you will observe that the area of
the spill no longer has a blue color. Is this
change chemical or physical? Give a reason for
your answer.
8. Inferring Gold and platinum are often used
to make jewelry. What can you infer about the
reactivity of these elements?
Scientific Methods Section 1.2 listed
typical steps scientists use. Which steps
might you use to decide whether a change
is physical or chemical? Explain.
Chapter 2
Section 2.3
Assessment
1. When the substances in a sample of matter
are changing into different substances
2. A change in color, the production of a gas,
or the formation of a precipitate
3. A chemical change produces new
substances. A physical change produces no
new substances.
4. When iron rusts, the compound that forms
is brittle.
5. Melting is a physical change. Burning is a
chemical change.
6. The raw egg is a viscous liquid. The egg
white is cloudy and the yolk is orange. The
hard-boiled egg is a soft solid. The egg white
is opaque and the yolk is yellow.
7. Because the bleach has caused the denim
to change color, the change is likely to be a
chemical change.
8. Because jewelry is designed to last a long
time, the reactivity of gold and platinum must
be relatively low.
What Should Be Done With
Arsenic-Treated Wood?
Termites are among the organisms that attack untreated wood. In 1950,
United States suppliers of lumber began to treat wood with a mixture of
copper, chromium, and arsenic (CCA). The mixture slows the damage to
wood by poisoning the attacking organisms. Outdoor structures such as
decks and porches were made from CCA-treated wood. By 2002, more than
95 percent of treated lumber sold for use outdoors contained CCA.
Arsenic is a poison that has been linked with certain types of cancer.
Arsenic can be absorbed through the skin or ingested in water or food.
Consumers were especially concerned about children touching CCA-treated
wood and then placing their unwashed fingers in their mouths. Some
consumers asked the Environmental Protection Agency (EPA) to ban the use
of CCA. In 2002, the chemical and home-improvement industries agreed to
stop producing CCA-treated wood for home use.
The Viewpoints
Old CCA-Treated Wood Does
Not Need to Be Removed
Old CCA-Treated Wood
Needs to Be Removed
The EPA did not recommend tearing down existing
structures made from CCA-treated wood. A panel
of Florida doctors reported that they found no
studies linking cancer in children and exposure to
CCA-treated wood. They concluded that the
amount of arsenic that children could absorb from
treated wood is small compared to the amount of
arsenic that occurs naturally in soil.
A report produced by one state’s Department of
Environmental Protection concluded that there is a
serious risk for children exposed to arsenic from
treated wood. The level of arsenic remains high for
20 years in CCA-treated wood. The useful life of
most treated wood products is about 20 years.
An area of CCA-treated wood the size of a
four-year-old’s hand contains about 120 times the
amount of arsenic allowed in a 6-ounce glass of
water. (The EPA limit for arsenic in drinking water is
10 parts per billion.) Rainwater penetrates wood
and dissolves arsenic. The arsenic ends up on the
surface of the wood or in the soil near the wood.
There are risks associated with disposing of
treated wood. Burning arsenic-treated wood
produces ash with high levels of arsenic. The ash
would poison a person who inhaled, ingested, or
touched it. The only acceptable method of disposal
is in landfills, which are rapidly filling. Also, arsenic
from landfills can end up in groundwater.
What Should Be Done With
L2
Arsenic-Treated Wood?
Background
Woods that are naturally resistant to
attack, such as cedar and redwood,
tend to be more expensive than timber
treated with CCA. Alternatives to
waterborne preservatives such as CCA
included creosote and pentachlorophenol, or penta. Creosote is a smelly
mixture of chemicals distilled from coal
tar. Railroads began to treat railroad ties
with creosote in 1889. Penta was
generally applied in a 5% solution of
petroleum solvents. Its use became
limited after the price of oil rose in the
1970s. Because there are health risks
associated with both penta and
creosote, their use has been restricted
since 1986.
After students answer Question 3, ask,
What evidence did the opponents and
supporters of CCA removal have that
you do not have? Explain how that
evidence might have influenced your
opinion. (The viewpoints as presented
were based on opposing interpretations of
scientific studies. Being able to see the actual
data might have influenced their opinions.)
Research and Decide
1. Defining the Issue In your own words,
describe the issue that needs to be resolved about
existing structures made from CCA-treated wood.
3. Forming Your Opinion Should existing structures built from CCA-treated wood be removed?
Which argument did you find most convincing?
2. Analyzing the Viewpoints List three
arguments of those who don’t think that existing
structures made from CCA-treated wood need to
be removed. List three arguments of those who
want to remove existing structures made from
CCA-treated wood.
Have students further research the
issues related to this topic.
For: More on this issue
Visit: PHSchool.com
Web Code: cch-1020
Properties of Matter 59
Answers
1. Are structures built from CCA-treated wood
enough of a health hazard for children that the
structures should be removed?
2. Old CCA-Treated Wood Does Not Need to
Be Removed: The EPA has not recommended
removal of the structures. No studies link cancer
in children and exposure to CCA-treated wood.
There are serious risks associated with disposal of
the wood.
Old CCA-Treated Wood Needs to Be Removed:
The level of arsenic remains high over the
lifetime of the wood. The level of arsenic in the
wood is much higher than the level allowed in
water. Rain causes arsenic to collect on the
surface of the wood or in soil.
3. Students should provide a reason for their
decision.
Properties of Matter 59