2.2 Physical Properties Section 2 - Physical Science

If 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 PropertiesA physical property is any characteristic of a material that can be

observed or measured without changing the composition of the sub-

stances in the material. Viscosity, conductivity, malleability,hardness, melting point, boiling point, and density are examplesof physical properties.

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.

2.2 Physical Properties

Reading StrategyBuilding Vocabulary Copy the table. Asyou read, write a definition for each property.

Key ConceptsWhat are some examplesof physical properties?

How can knowing thephysical properties ofmatter be useful?

What processes are usedto separate mixtures?

Vocabulary� physical property� viscosity� conductivity� malleability� melting point� boiling point� filtration� distillation� physical change

Viscosity

Malleability

Melting point

Physical Property Definition

a. ?

b. ?

c. ?

Properties of Matter 45

Figure 9 The object in thephotograph is called a honeydipper. Honey is an example of aliquid with a high viscosity.

FOCUS

Objectives2.2.1 Describe physical properties of

matter.2.2.2 Identify substances based on

their physical properties.2.2.3 Describe how properties are

used to choose materials.2.2.4 Describe methods used to

separate mixtures.2.2.5 Describe evidence that

indicates a physical change istaking place.

Build VocabularyLINCS Have students use the LINCSstrategy to learn and review the termsviscosity, conductivity, and malleability. InLINCS exercises, the students List whatthey know about each term, Imagine apicture that describes the word or phrase,Note a reminding “sound-alike” word(such as visible, train conductor, andmallet), Connect the terms to the sound-alike word by making up a short story,and then perform a brief Self-test.

Reading Strategya. The tendency of a liquid to resistflowing b. The ability of a solid to behammered without shattering c. Thetemperature at which a substancechanges from a solid to liquid

INSTRUCT

Examples of Physical PropertiesFYIThe text mentions that lemonade can be identified by its taste. Remind stu-dents that taste should never be used toidentify an unknown substance and thatno substances, known or unknown,should ever be ingested in a lab.

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Reading Focus

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Print• Laboratory Manual, Investigation 2B• Reading and Study Workbook With

Math Support, Section 2.2 and Math Skill: Melting and Boiling Points

• Transparencies, Section 2.2

Technology• Interactive Textbook, Section 2.2• Presentation Pro CD-ROM, Section 2.2• Go Online, Science News, Properties of

matter

Section Resources

Section 2.2

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 mal-

leable. 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 stirhot soup?

Comparing Heat Conductors

Materials2 plastic foam cups, scissors, metric ruler, metalrod, wooden rod, 2 liquid crystal thermometers,hot water, clock or watch with second hand

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 cupupside down. Use the metal rod to make twoholes about 3 cm apart in the bottom.

3. Attach a thermometer to each rod as shown.

4. Insert both rods so they will just touch thebottom of the second cup. Lay the cup withthe rods on the table. Do not touch the rodsand thermometers during the experiment.

5. Ask your teacher to add hot water to theintact cup until it is about three fourths full.

6. Hold the cup with the hot water firmly as youplace the cup with the rods on top of it.CAUTION Be careful not to overturn the cup.

7. Observe and record the temperatures everyminute for five minutes.

Analyze and Conclude1. Comparing and Contrasting Is metal or

wood a better conductor of heat? Explain.

2. Applying Concepts Is a metal cup a goodcontainer for keeping a drink hot for as long aspossible? Give a reason for your answer.

3. Evaluating Describe any variables, otherthan the type of material, that were notcontrolled in this lab.

Liquid crystalthermometer

Metal rod

Wooden rod

Foam cups

46 Chapter 2

Figure 10 Because gold is bothmalleable and beautiful, it isoften used to make jewelry. Theseancient gold medallions weremade to form a necklace.

46 Chapter 2

Comparing Heat Conductors

ObjectiveAfter completing this activity, studentswill be able to• distinguish a material that is a good

conductor of heat from a material thatis a poor conductor of heat.

Skills Focus Observing, Inferring

Prep Time 10 minutes

Advance Prep Acquire wood andmetal rods of similar length from themetal or woodworking classroom, a crafts shop, or a home repair shop. Liquid crystal thermometers may bepurchased at a pet or aquarium supplystore. You may want to cut the cups andattach the thermometers to the rods inadvance to save class time. Thermom-eters can be attached to the rods withtheir own adhesive backing or taped on.Heat enough water to fill each foam cupabout 3/4 full.

Class Time 20 minutes

Safety Remind students to handle thesetup carefully to prevent burns after thehot 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 groupenter its data in this table. All data can then be pooled and averaged for greater accuracy.

Expected Outcome Metal willconduct heat faster than wood.

Analyze and Conclude1. Metal is a better conductor. Studentsshould cite the differences in temperatureover time as evidence.2. Metal is not the best choice for thispurpose. Because metals are good con-ductors, the contents of the cup willcool quickly as heat is transferred to the surroundings.3. Depending on what rods are used,possible sources of error are differentlengths, different diameters, anddifferent densities of the materials.Kinesthetic, Logical

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Section 2.2 (continued)

Customize for Inclusion Students

Visually Impaired Provide students who have visual impairmentswith samples of two different nontoxic solidsthat have approximately the same mass. Byhandling the samples, students can infer theirrelative densities from their volumes.

Provide samples of materials with a range of hardness. Have students do scratch tests to determine an order of hardness. Studentsshould be able to feel any indentations on thesurfaces of the softer materials.


Hardness One way to compare the hardness of two materials is to

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 at sea level, the water will 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.

Density Density can be used to test the purity of a substance. Recall

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 per-

cent 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 Boiling Point

Hydrogen

Nitrogen

Ammonia

Octane (found in gasoline)

Water

Acetic acid (found in vinegar)

Table salt

Gold

�259.3�C

�210.0�C

�77.7�C

�56.8�C

0.0�C

16.6�C

800.7�C

1064.2�C

�252.9�C

�195.8�C

�33.3�C

125.6�C

100.0�C

117.9�C

1465�C

2856�C

Melting and Boiling Points of Some Substances

Substance

Figure 12 The table lists themelting points and boiling pointsfor several substances.Analyzing Data Which of thesesubstances are liquids at roomtemperature (20oC, or 68oF)?

Figure 11 This Tlingit carver isusing an adze to carve a canoefrom Western red cedar. Redcedar is a relatively soft wood.

Use VisualsFigure 10 Gold is the most malleablemetal. Ancient Greek jewelry was oftenhammered 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 beshaped into small, detailed pieces.) Themedallions shown in Figure 10 werefound in the Lazlo region of central Italyand were likely made between the eighthand sixth centuries B.C. Ask, Given theage of this jewelry, what other prop-erty could you say gold exhibits? (Gold is durable.)Visual

Integrate Earth ScienceThere are different scales for describinghardness. The Brinell and Rockwell scalesare based on the indentation made by anobject. The Brinell hardness number isbased on indentation depth. The Rockwellhardness number is based on indentationarea. On a scale that measures resistanceto abrasion, only two substances are ratedabove 10: cubic boron nitride (cBN), 19,and diamond, 42.5. Have students findout about hardness scales and describehow they are used to characterize rocksand minerals.Logical, Portfolio

FYIBoiling points depend on bothtemperature and pressure. In Chapter 3,students will study the effect of pressureon boiling points.

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Answer to . . .

Figure 12 Octane, water, and acetic acid

A wooden spoon is apoor conductor of heat.

Specific Gravity The AMA race officialsdescribed in the text are using a hygrometerto test specific gravity. Specific gravity is theratio of the mass of a solid or liquid to themass of an equal volume of distilled water

at 4°C. Because specific gravity is a ratio ofvalues that have identical units, it does nothave units. (Density is discussed in greaterdetail in Chapter 1.)

Facts and Figures

Using Physical PropertiesPeople use data about physical properties to solve many different types

of problems. Physical properties are used to identify a material, tochoose a material for a specific purpose, or to separate the substancesin a mixture.

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-and-

run 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.

Using Properties to Choose Materials Properties deter-

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.

Figure 13 Shoelaces for hikingboots are sometimes made fromleather. So are some belts andshoes. Making GeneralizationsWhat properties of leather wouldmake it a suitable material for allthree types of objects?

48 Chapter 2

48 Chapter 2

Using PhysicalPropertiesBuild Reading LiteracyOutline Refer to page 156D inChapter 6, which provides theguidelines for an outline.

Have students read pp. 48–50 andgather information on identifying,choosing, and separating substancesbased on their physical properties. Then,have students use the headings as majordivisions in an outline. Have studentsrefer to their outlines when answeringthe questions in the Section 2.2Assessment. Visual

Comparing Melting PointsPurpose Students observe thedifferences in melting points of twosubstances.

Materials water, ethanol, foam cups,freezer, large beaker, thermometer

Procedure Tell students that you willdemonstrate that the melting points oftwo substances differ. The night before,place a foam cup filled with water and asecond foam cup filled with ethanol inthe freezer. During class, pull both cupsout of the freezer. Have students notethat the water is frozen, but the ethanolis not. Remove the ice from the cup andadd it to the large beaker. Add a smallamount of water and allow the ice tobegin melting. While the temperature of the ice water is leveling off, have avolunteer measure the temperature ofthe ethanol. Compare that temperatureto the temperature of the ice water.

Expected Outcome Because mostfreezers do not cool to temperaturesbelow the melting point of ethanol,–114.7°C, the ethanol will remain aliquid. After some of the ice has melted,the temperature of the solid-liquidsystem will stop decreasing and level off. This is the melting point of water,0°C. The temperature of the chilledethanol is below 0°C. Visual

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Identifying Substances Sometimes a singleproperty is not sufficient to positively identify asubstance. Iron, nickel, and cobalt, which areoften found together in nature, look quitesimilar. The density of iron is 7.87 g/cm3. Thedensity of nickel is 8.90 g/cm3. The density of

cobalt is 8.86 g/cm3. Measurements of massmade on the type of balance found in mostschool labs would be precise enough to distinguish iron from cobalt or nickel, butnot precise enough to distinguish cobalt from nickel.

Facts and Figures

Making a SculptureA process called lost-wax casting is used to make metalsculptures. Different stages of the process depend onphysical properties of wax, clay, and metal. Wax can becarved and molded. Clay becomes brittle when baked ata high temperature. When melted, most metals formhomogeneous mixtures, which can be poured into molds.Interpreting Diagrams Why is it important that wax hasa low melting point?

Preparing clay moldsThis artist from Nepal in southernAsia is preparing molds for lost-waxcasting. She is applying layers of clayto a wax model.

Wax model A wax model ofthe sculpture is built up around

a clay core. Wax is used because it issoft enough for carving fine details,but hard enough to retain its shapeat room temperature.

Clay moldClay is applied to

the wax model in layersof increasing coarseness,and left to dry. The inner,finer layers capture everydetail of the sculpture ina smooth mold. Theouter, coarser layers(clay mixed with sand)provide strength.

Molten metalMolten (liquid)

metal is poured into theclay mold and left tocool and harden. For thissculpture of an Africanhead, a mixture ofcopper, zinc, and leadwas used.

Metal sculptureWhen the metal

has cooled, the clayshell is broken open toreveal the finishedmetal sculpture.

Melting waxThe clay-covered

wax model is thenbaked in a kiln. Becausewax has a low meltingpoint, the wax modelmelts away inside theclay, leaving a hardenedshell mold. This claymold is then used tomake the final sculpture.

Molten metalpoured intomold

Layers of clayapplied to thewax model

Wax model

Clay core

Meltingwax

Wax model

Broken clay

Cast metalsculpture


Making a SculptureThere are a number of variations to the method described in the text. Forexample, sometimes there is no claycore. The lost-wax method of castingcan also be used to make replicas ofexisting sculptures.

Many other molding and castingtechniques also take advantage of the physical properties of differentsubstances to maximize the quality of the final product. For example, theproperties of some types of rubber makethem ideal materials for molds. Rubbermolds are flexible enough that the castcan be pulled out without breaking themold, yet strong enough to preservefine details in the final product. Becauseof their durability, rubber molds can bereused many times.

Interpreting Diagrams The waxmust melt away when the model isheated in a kiln.Logical

For EnrichmentBecause an imprint made in wet sandwill hold its shape, filling the imprintwith melted wax or wet plaster willproduce a cast of the object pressed intothe sand. This sculpting technique iscalled a sand mold. Have students findout about sand molds and use them tomake candles or plaster casts of theirfootprints or handprints.Visual, Portfolio

Use Community ResourcesArrange for a sculptor or jewelry makerto visit the class. Have the artist describethe molding and casting techniques he or she uses. Before the visit, havestudents prepare questions about howthe artist chooses materials based ontheir physical properties.Interpersonal

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Answer to . . .

Figure 13 Flexibility and durability

50 Chapter 2

Using Properties to Separate MixturesSome properties can be used to separate mixtures. Filtration anddistillation are two common separation methods.

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, dis-

solve 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 fil-

tration. 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.

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 sepa-

rates the substances in a solution based on their boiling points.

One practical use of distillation is to provide fresh water for sub-

marines. 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 sep-

arate 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 apot of brewed tea?

Figure 14 These Americorpsstudents are looking for artifactsat the San Diego Presidio—a fortthat was built in 1769. As thestudents sift dirt through ascreen, small objects buried in thedirt collect on the screen.Applying Concepts How couldchanging the size of the holes ina screen change the number ofobjects found?

For: Articles on propertiesof matter

Visit: PHSchool.com

Web Code: cce-1022

50 Chapter 2

Using Properties toSeparate MixturesBuild Science Skills

Applying Concepts

Purpose In this activity, students use properties to separate the components of a mixture.

Materials a mixture of table salt, sand,and iron filings; beaker; magnet; plasticbag; water; funnel; filter paper

Class Time 20 minutes

Procedure Encourage students toconsider properties that can be used toseparate each material from the othertwo materials in the mixture. Then, havestudents design a procedure tocomplete the separation.

Expected Outcome Students cancollect the iron filings using a magnetcovered with a plastic bag. They can addwater to the mixture to dissolve the salt.They can use a filter to collect the sand.Students can collect the salt by lettingthe water evaporate for a few days. Visual, Portfolio

Students may think that all the particlesin mixtures are similar in size. This is truefor solutions and colloids, but not forsuspensions. Challenge this miscon-ception by displaying common devicesused to filter mixtures (such as a sieve, a colander, and a coffee filter) anddiscussing the mixtures these devicesare used to separate. The size of theholes in a filter determines whetherfiltration can be used to separate asuspension. Hole size also determineswhether all the particles in a colloid pass through the filter or all the particlesare trapped in the filter. Either way, theend result is that the colloid is notseparated by filtration.Verbal

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Science News provides studentswith current information onproperties of matter.

Tea Tea contains compounds calledpolyphenols, which are often referred to astannins. There are health claims made for bothblack and green tea. The health claims madefor green tea are related to the concentrationof 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 dumpedinto Boston harbor on December 16, 1773,was green tea, which outsold black tea in the Colonies.)

Facts and Figures

Section 2.2 Assessment

Reviewing Concepts1. List seven examples of physical properties.

2. Describe three uses of physical properties.

3. Name two processes that are used toseparate mixtures.

4. When you describe a liquid as thick, are yousaying that it has a high or a low viscosity?

5. Explain why sharpening a pencil is an exampleof a physical change.

6. What allows a mixture to be separatedby distillation?

Critical Thinking7. Designing Experiments How could you

find out whether copper is harder or softerthan the plastic used in a plastic cup?

8. Inferring Why would you expect thematerials used to make pot holders to bepoor conductors of heat?

9. Applying Concepts Silicon dioxide is asolid at room temperature and methanolis a liquid. Which substance has the highermelting point?

Organizing Data In what order are thesubstances arranged in Figure 12? Usewhat you studied about organizing data inSection 1.4 to explain why this order isuseful. Explain why you might choose adifferent order if you had similar data for500 substances.

Figure 15 Braiding hair andcutting hair are examples ofphysical changes. Braiding is areversible change. Cutting cannotbe reversed.

Recognizing Physical ChangesThe 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 exam-

ples 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.


Recognizing Physical ChangesFYIIf butter heated in a pan begins tobrown, this is a sign that a chemicalchange is starting to occur. Students areasked to compare the possible changesto heated butter in Question 5 of theSection 2.3 Assessment.

ASSESSEvaluate UnderstandingTell students that a layer of fat rises tothe 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.)

ReteachUse the How It Works feature on p. 49to review with students the importanceof examining physical properties whenchoosing a material. Discuss why thephysical properties of wax, clay, andmetal determine what roles they play inthe making of a sculpture.

The substances are ordered from lowestto highest melting point, which groupsthem into gases, liquids, and solids atroom temperature. With a largerdatabase, alphabetical order would bemore useful for retrieving the data.

If your class subscribes to the InteractiveTextbook, use it to review key conceptsin Section 2.2.

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5. The shape and size of the pencil change,but the composition of the pencil remains the same.6. A difference in boiling points allowsmixtures to be separated by distillation.7. By scratching the cup with an object madeof copper8. Pot holders are designed to prevent thetransfer of heat from a cooking utensil.9. Silicon dioxide

Section 2.2 Assessment

1. Students may list hardness, viscosity,conductivity, density, malleability, meltingpoint, and boiling point. Students may also list color, taste, flexibility, and durability.2. Identify materials, choose a material for aspecific purpose, or separate the substances in a mixture3. Filtration and distillation4. A thick liquid has a high viscosity.

Answer to . . .

Figure 14 With smaller holes, moreobjects would collect on the screen.

Loose tea leaves can beremoved by filtration.

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2.2 Physical Properties Section 2 - Physical Science