r e t p a 2 t h e p ro p e rtie s o f m a tte r h...

The Properties of Matter

Imagine . . .The year is 1849. You are one of thousandsof people who have come to California toprospect for gold. You left home severalmonths ago in the hopes of striking it rich.But so far, no luck. In fact, you’ve decidedthat if you don’t find gold today, you’re goingto pack up your things and head back home.

You swing your pickax into the granitebedrock, and a bright flash catches your eye.The flash is caused by a shiny yellow chunksticking out of the rock. When you firststarted prospecting, such a sight made youcatch your breath. Now you just sigh. Morefool’s gold, you think.

Fool’s gold is the nickname for iron pyrite(PIE RIET), a mineral that looks like gold andis found in the same areas of Californiawhere gold is found. But iron pyrite differsfrom gold in several ways. When hit with ahammer, iron pyrite shatters into pieces, andsparks fly everywhere. Gold just bends whenit is hit, and no sparks are produced. Ironpyrite also produces foul-smelling smokewhen it is heated. Gold does not.

Chapter 234

CH

AP

TE

R

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Can You Tell the Difference?One of these rock samplescontains gold that is worthhundreds of dollars. The other rocksample contains iron pyrite that is worthabout . . . well, nothing.

Copyright © by Holt, Rinehart and Winston. All rights reserved.

The Properties of Matter 35

You perform a few quick tests on yourshiny find. When you hit it with a hammer,it bends but does not shatter, and no sparksare produced. When you heat it, there is nosmoke or odor. You start to get excited. You’llhave to perform a few more tests when youget back to town, but this time you’re almostcertain that you’ve struck gold. Congratu-lations! Your knowledge of the different char-acteristics, or properties, of fool’s gold andreal gold has finally paid off.

In this chapter you’ll learn more aboutthe many different properties that objectscan have and why these properties areimportant to know.

Sack SecretsIn this activity, you will test your skills in determin-ing the identity of an object based on its properties.

Procedure1. You and two or three of your classmates will

receive a sealed paper sack with a number onit. Write the number in your ScienceLog. Insidethe sack is a mystery object. Do not open thesack!

2. For 5 minutes, make as many observations asyou can about the object. You may shake thesack, touch the object through the sack, listento the object in the sack, smell the objectthrough the sack, and so on. Be sure to writedown your observations.

Analysis3. At the end of 5 minutes,

take a couple of minutes to discuss your findings withyour partners.

4. With your partners, list theobject’s properties, and make a conclusion about the object’sidentity. Write your conclusion inyour ScienceLog.

5. Share your observations, list of properties, andconclusion with the class. Now you are readyto open the sack.

6. Did you properly identify the object? If so, how?If not, why not? Write your answers in yourScienceLog, and share them with the class.

In your ScienceLog, try to answer the following questions based on what youalready know:

1. What is matter?

2. What is the difference between aphysical property and a chemicalproperty?

3. What is the difference between aphysical change and a chemicalchange?


Chapter 236

N E W T E R M Smatter gravityvolume weightmeniscus newtonmass inertia

O B J E CT I V E S! Name the two properties of all

matter.! Describe how volume and mass

are measured.! Compare mass and weight.! Explain the relationship between

mass and inertia.

Section1 What Is Matter?

Here’s a strange question: What doyou have in common with a toaster?

Do you give up? Okay, here’sanother question: What do you havein common with a steaming bowl ofsoup or a bright neon sign?

You are probably thinking these are trickquestions. After all, it is hard to imagine thata human—you—has anything in common witha kitchen appliance, some hot soup, or a glowingneon sign.

From a scientific point of view, however, you haveat least one characteristic in common with these things. You,the toaster, the bowl, the soup, the steam, the glass tubing,and the glowing gas are all made of matter. In fact, everythingin the universe that you can touch (even if you cannot see it)is made of matter. For example, DNA, microscopic bacteria,and even air are all made of matter. But what is matter exactly?If so many different kinds of things are made of matter, youmight expect the definition of the word matter to be compli-cated. But it is really quite simple. Matter is anything that hasvolume and mass.

Matter Has VolumeAll matter takes up space. The amount of space taken up, oroccupied, by an object is known as the object’s volume. Thesun, shown in Figure 1, has volume because it takes up spaceat the center of our solar system. Your fingernails have vol-ume because they occupy space at the end of your hands.(The less you bite them, the more volume they have!)Likewise, the Statue of Liberty, the continent of Africa, anda cloud all have volume. And because these thingshave volume, they cannot share the same spaceat the same time. Even the tiniest speck ofdust takes up space, and there’s no wayanother speck of dust can fit into thatspace without somehow bumping thefirst speck out of the way. Try theQuickLab on this page to see for your-self that matter takes up space—evenmatter you can’t see.

Space Case1. Crumple a piece of paper,

and fit it tightly in thebottom of a cup so that itwon’t fall out.

2. Turn the cup upside down.Lower the cup straightdown into a large beakeror bucket half-filled withwater until the cup is allthe way underwater.

3. Lift the cup straight out ofthe water. Turn the cupupright and observe thepaper. Record your obser-vations in your ScienceLog.

4. Now punch a small hole in the bottom of the cupwith the point of a pencil.Repeat steps 2 and 3.

5. How do these results showthat air has volume?Record your explanation inyour ScienceLog.

Figure 1 The volume of the sun isabout 1,000,000 (1 million) timeslarger than the volume of the Earth.


Liquid Volume Locate the Great Lakes on a map of the UnitedStates. Lake Erie, the smallest of the Great Lakes, has a volumeof approximately 483,000,000,000,000 (483 trillion) litersof water. Can you imagine that much liquid?Well, think of a 2 liter bottle of soda. Thewater in Lake Erie could fill more than 241trillion of those bottles. That’s a lot of water!On a smaller scale, a can of soda has a vol-ume of only 355 milliliters, which is approxi-mately one-third of a liter. The next time yousee a can of soda, you can read the volumeprinted on the can. Or you can check its volume bypouring the soda into a large measuring cup from yourkitchen, as shown in Figure 2, and reading the scale at thelevel of the liquid’s surface.

Measuring the Volume of Liquids In your scienceclass, you’ll probably use a graduated cylinder to meas-ure the volume of liquids. Keep in mind that the sur-face of a liquid in a graduated cylinder is not flat. Thecurve that you see at the liquid’s surface has a specialname—the meniscus (muh NIS kuhs). When you measurethe volume of a liquid, you must look at the bottom of themeniscus, as shown in Figure 3. (A liquid in any container,including a measuring cup or a large beaker, has a menis-cus. The meniscus is just too flat to see in a wider container.)

Liters (L) and milliliters (mL)are the units used most often toexpress the volume of liquids.The volume of any amount ofliquid, from one raindrop to acan of soda to an entire ocean,can be expressed in these units.

Measuring the Volume of Solids What would you do ifyou wanted to measure the volume of this textbook? You can-not pour this textbook into a graduated cylinder to find theanswer (sorry, no shredders allowed!). In the MathBreak activ-ity on the next page, you will learn an easy way to find thevolume of any solid object with rectangular sides.


Figure 2 If the measurementis accurate, the volume

measured should bethe same as the

volume printedon the can.

The volume of a typicalraindrop is approximately0.09 mL, which means that it would take almost 4,000raindrops to fill a soda can.

Meniscus

Figure 3 To measure volume correctly,read the scale at the lowest part of themeniscus (as indicated) at eye level.


The volume of any solidobject, from a speck of dust to the tallest skyscraper, isexpressed in cubic units.The term cubic means “hav-ing three dimensions.” (Adimension is simply a meas-urement in one direction.)The three dimensions thatare used to find volume arelength, width, and height,as shown in Figure 4.

Cubic meters (m3) andcubic centimeters (cm3) arethe units most often usedto express the volume of solid items. In the unit abbreviationsm3 and cm3, the 3 to the upper right of the unit shows thatthe final number is the result of multiplying three quantitiesof that unit.

You now know that the volumes of solids and liquids areexpressed in different units. So how can you compare the vol-ume of a solid with the volume of a liquid? For example, sup-pose you are interested in determining whether the volumeof an ice cube is equal to the volume of water that is left whenthe ice cube melts. Well, lucky for you, 1 mL is equal to 1 cm3. Therefore, you can express the volume of the water incubic centimeters and compare it with the original volume ofthe solid ice cube. The volume of any liquid can be expressedin cubic units in this way. (However, keep in mind that in SI,volumes of solids are never expressed in liters or milliliters.)

Measuring the Volume of Gases How do you measure thevolume of a gas? You can’t hold a ruler up to a gas to meas-ure its dimensions. You can’t pour a gas into a graduated cylin-der. So it’s impossible, right? Wrong! A gas expands to fill itscontainer. If you know the volume of the container that a gasis in, then you know the volume of the gas.

Matter Has MassAnother characteristic of all matter is mass. Mass is the amountof matter in a given substance. For example, the Earth con-tains a very large amount of matter and therefore has a largemass. A peanut has a much smaller amount of matter andthus has a smaller mass. Remember, even something as smallas a speck of dust is made of matter and therefore has mass.

38

Calculating VolumeA typical compact disc (CD)case has a length of 14.2 cm,a width of 12.4 cm, and aheight of 1.0 cm. The volumeof the case is the lengthmultiplied by the width multi-plied by the height:

14.2 cm ! 12.4 cm !1.0 cm " 176.1 cm3

Now It’s Your Turn1. A book has a length of

25 cm, a width of 18 cm,and a height of 4 cm. Whatis its volume?

2. What is the volume of asuitcase with a length of95 cm, a width of 50 cm,and a height of 20 cm?

3. For additional practice, find the volume of otherobjects that have square orrectangular sides. Compareyour results with those ofyour classmates.

MATH BREAK

How would you measurethe volume of this

strangely shapedobject? To find out,

turn to page 520in the LabBook.

1m

1 m

!

"

! "! "1 m

Chapter 2

Figure 4 A cubic meter has aheight of 1 m, a length of 1 m,and a width of 1 m, so its vol-ume is 1 m ! 1 m ! 1 m " 1 m3.

1 m3


An object’s mass can be changed only bychanging the amount of matter in the object.Consider the bowling ball shown in Figure 5.Its mass is constant because the amount ofmatter in the bowling ball never changes (unlessyou use a sledgehammer to remove a chunk ofit!). Now consider the puppy. Does its massremain constant? No, because the puppy isgrowing. If you measured the puppy’s massnext year or even next week, you’d findthat it had increased. That’s because morematter—more puppy—would be present.

The Difference Between Mass and WeightWeight is different from mass. To understand this difference,you must first understand gravity. Gravity is a force of attrac-tion between objects that is due to their masses. This attrac-tion causes objects to experience a “pull” toward other objects.Because all matter has mass, all matter experiences gravity. Theamount of attraction objects experience toward each otherdepends on two things—the masses of the objects and the dis-tance between them, as shown in Figure 6.

Gravitational force is smaller between objects with smallermasses that are close together than between objects with largemasses that are close together (as shown in a).

An increase in distance reduces gravitational force between twoobjects. Therefore, gravitational force between objects with largemasses (such as those in a) is less if they are far apart.


Imagine the following itemsresting side by side on atable: an elephant, a tennisball, a peanut, a bowling ball,and a housefly. In yourScienceLog, list these items inorder of their attraction tothe Earth due to gravity, fromleast to greatest amount ofattraction. Follow your listwith an explanation of whyyou arranged the items in theorder that you did.

Figure 6 How Mass and Distance Affect Gravity Between Objects

Gravitational force (represented by the width of the arrows) islarge between objects with large masses that are close together.

a

b

c

Figure 5 The mass of thebowling ball does notchange. The mass of thepuppy increases as morematter is added—that is, asthe puppy grows.


May the Force Be with You Gravitational force is experi-enced by all objects in the universe all the time. But the ordi-nary objects you see every day have masses so small (relativeto, say, planets) that their attraction toward each other is hardto detect. Therefore, the gravitational force experienced byobjects with small masses is very slight. However, the Earth’smass is so large that the attraction of other objects to it isgreat. Therefore, gravitational force between objects and theEarth is great. In fact, the Earth is so massive that our atmos-phere, satellites, the space shuttle, and even the moon experi-ence a strong attraction toward the Earth. Gravity is what keepsyou and everything else on Earth from floating into space.

So What About Weight? Weight is simply a measure of thegravitational force on an object. Consider the brick in Figure 7.The brick has mass. The Earth also has mass. Therefore, thebrick and the Earth are attracted to each other. A force is exerted

on the brick because of its attraction to the Earth. Theweight of the brick is a measure of this gravita-

tional force. Now look at the sponge in Figure 7. The

sponge is the same size as the brick, but itsmass is much less. Therefore, the sponge’sattraction toward the Earth is not as great,and the gravitational force on it is not as great.Thus, the weight of the sponge is less thanthe weight of the brick.

Because the attraction that objects experi-ence decreases as the distance between themincreases, the gravitational force on objects—and therefore their weight—also decreases as

the distance increases. For this reason, a brickfloating in space would weigh less than it does rest-

ing on Earth’s surface. However, the brick’s mass wouldbe the same in space as it is on Earth.

Massive Confusion Back on Earth, the gravitational forceexerted on an object is about the same everywhere, so anobject’s weight is also about the same everywhere. Becausemass and weight remain constant everywhere on Earth, theterms mass and weight are often used as though they meanthe same thing. But using the terms interchangeably can leadto confusion, especially if you are trying to measure theseproperties of an object. So remember, weight depends on mass,but weight is not the same thing as mass.

Chapter 240

life scienceC O N N E C T I O N

The mineral calcium is storedin bones, and it accounts forabout 70 percent of the massof the human skeleton. Cal-cium strengthens bones, help-ing the skeleton to remainupright against the strongforce of gravity pulling ittoward the Earth.

Figure 7This brick and sponge may be the same size, but their masses, and therefore theirweights, are quite different.

across the sciencesC O N N E C T I O N

Some scientists think thatthere are WIMPs in space.Find out more on page 56.


Measuring Mass and WeightThe SI unit of mass is the kilogram (kg), but mass is oftenexpressed in grams (g) and milligrams (mg) as well. These unitscan be used to express the mass of any object, from a singlecell in your body to the entire solar system. Weight is a meas-ure of gravitational force and must be expressed in units offorce. The SI unit of force is the newton (N). So weight isexpressed in newtons.

A newton is approximately equal to the weight of a 100 gmass on Earth. So if you know the mass of an object, you cancalculate its weight on Earth. Conversely, if you know theweight of an object on Earth, you can determine its mass.Figure 8 summarizes the differences between mass and weight.


Mass is . . .! a measure of the amount of

matter in an object.

! always constant for an objectno matter where the object isin the universe.

! measured with a balance(shown below).

! expressed in kilograms (kg),grams (g), and milligrams (mg).

Weight is . . .! a measure of the gravitational

force on an object.

! varied depending on wherethe object is in relation to theEarth (or any other large bodyin the universe).

! measured with a spring scale(shown above).

! expressed in newtons (N).

Figure 8 Differences Between Mass and Weight

Self-CheckIf all of your schoolbooks combined havea mass of 3 kg, what istheir total weight innewtons? Rememberthat 1 kg = 1,000 g.(See page 596 to checkyour answer.)


Mass Is a Measure of InertiaWhich do you think would be easier to pick up and throw, asoccer ball or a bowling ball? Well, you could probably throwthe soccer ball clear across your backyard, but the bowling ballwould probably not go very far. What’s the difference? Thedifference has to do with inertia (in UHR shuh). Inertia is thetendency of all objects to resist any change in motion. Because

of inertia, an object at rest (like the soccer ball or the bowl-ing ball) will remain at rest until something causes it tomove. Likewise, a moving object continues to move atthe same speed and in the same direction unless some-thing acts on it to change its speed or direction.

So why do we say that mass is a measure of inertia? Well, think about this: An object with a largemass is harder to start in motion and harder to stopthan an object with a smaller mass. This is becausethe object with the large mass has greater inertia.For example, imagine that you are going to push agrocery cart that has only one potato in it. No prob-

lem, right? But suppose the grocery cart is filled withpotatoes, as in Figure 9. Now the total mass—and the

inertia—of the cart full of potatoes is much greater. It willbe harder to get the cart moving and harder to stop itonce it is moving. So an object with a large mass hasgreater inertia than an object with a smaller mass.

1. What are the two properties of all matter?

2. How is volume measured? How is mass measured?

3. Analyzing Relationships Do objects with large massesalways have large weights? Explain your reasoning.

Chapter 242

Ordinary bathroom scales are spring scales. Manyscales available today show a reading in both

pounds (a common though not SI unit of weight) andkilograms. How does such a reading contribute to theconfusion between mass and weight?

REVIEW

Figure 9 Why is a cartload ofpotatoes harder to get movingthan a single potato? Because of inertia, that’s why!



Describing MatterHave you ever heard of the game called “20 Questions”? Inthis game, your goal is to determine the identity of an objectthat another person is thinking of by asking questions aboutthe object. The other person can respond with only a “yes”or “no.” If you can identify the object after asking 20 or fewerquestions, you win! If you still can’t figure out the object’sidentity after asking 20 questions, you may not be asking theright kinds of questions.

What kinds of questions should you ask? You might findit helpful to ask questions about the properties of the object.Knowing the properties of an object can help you determinethe object’s identity, as shown below.

Physical PropertiesSome of the questions shown above help the asker gatherinformation about color (Is it orange?), odor (Does it have anodor?), and mass and volume (Could I hold it in my hand?).Each of these properties is a physical property of matter. Aphysical property of matter can be observed or measured with-out changing the identity of the matter. For example, youdon’t have to change what the apple is made of to see that itis red or to hold it in your hand.

Could I hold it in my hand?

Yes.

Does it have an odor? Yes.

Is it safeto eat?

Yes.

Yes.Is it anapple?

No. No. Yes.

Is it orange?Yellow? Red?

N E W T E R M Sphysical property physical changedensity chemical changechemical property

O B J E CT I V E S! Give examples of matter’s differ-

ent properties.! Describe how density is used to

identify different substances.! Compare physical and chemical

properties.! Explain what happens to matter

during physical and chemicalchanges.

Section2

With a partner, play a gameof 20 Questions. One personwill think of an object, andthe other person will askyes/no questions about it.Write the questions in yourScienceLog as you go along.Put a check mark next to thequestions asked about physi-cal properties. When theobject is identified or whenthe 20 questions are up,switch roles. Good luck!


You rely on physical properties all the time. For example,physical properties help you determine whether your socks areclean (odor), whether you can fit all your books into yourbackpack (volume), or whether your shirt matches your pants(color). The table below lists some more physical propertiesthat are useful in describing or identifying matter.

Spotlight on Density Density is a very helpful property whenyou need to distinguish different substances. There are some

interesting things you should know about den-sity. Look at the definition of density in the

table above—mass per unit volume. If youthink back to what you learned inSection 1, you can define density inother terms: density is the amount ofmatter in a given volume, as shown inFigure 10.

44

Definition

The ability to transferthermal energy fromone area to another

The physical form inwhich a substanceexists, such as a solid,liquid, or gas

The ability to bepounded into thinsheets

The ability to be drawnor pulled into a wire

The ability to dissolvein another substance

Mass per unit volume

Example

Plastic foam is a poorconductor, so hotchocolate in a plastic-foam cup will not burnyour hand.

Ice is water in its solidstate.

Aluminum can berolled or pounded intosheets to make foil.

Copper is often used to make wiring.

Sugar dissolves in water.

Lead is used to makesinkers for fishing linebecause lead is moredense than water.

Physical property

Thermal conductivity

State

Malleability (MAL ee uh BIL uh tee)

Ductility(duhk TIL uh tee)

Solubility(SAHL yoo BIL uh tee)

Density

Chapter 2

Figure 10A golf ball ismore dense thana table-tennisball because thegolf ball containsmore matter in asimilar volume.

More Physical Properties


To find an object’s density (D), first measure its mass (m)and volume (V). Then use the following equation:

D = !mV!

Units for density are expressed using a mass unit divided bya volume unit, such as g/cm3, g/mL, kg/m3, and kg/L.

Using Density to Identify Substances Density is a usefulproperty for identifying substances for two reasons. First, thedensity of a particular substance is always the same at a givenpressure and temperature. For example, the helium in a hugeairship has a density of 0.0001663 g/cm3 at 20!C and normalatmospheric pressure. You can calculate the density of anyother sample of helium at that same temperature and pres-sure—even the helium in a small balloon—and you will get0.0001663 g/cm3. Second, the density of one substance is usu-ally different from that of another substance. Check out thetable below to see how density varies among substances.

Do you remember your imaginaryattempt at gold prospecting? To makesure you hadn’t found more fool’sgold (iron pyrite), you could comparethe density of a nugget from yoursample, shown in Figure 11, with theknown densities for gold and ironpyrite at the same temperature andpressure. By comparing densities,you’d know whether you’d actuallystruck gold or been fooled again.


DensityYou can rearrange the equa-tion for density to find massand volume as shown below:

D " !mV!

m " D # V V " !mD!

1. Find the density of a sub-stance with a mass of 5 kgand a volume of 43 m3.

2. Suppose you have a leadball with a mass of 454 g.What is its volume? (Hint:Use the table at left.)

3. What is the mass of a 15 mL sample of mercury?(Hint: Use the table at left.)

MATH BREAK

Pennies minted before 1982are made mostly of copperand have a density of 8.85 g/cm3. In 1982, apenny’s worth of copperbegan to cost more thanone cent, so the U.S.Department of the Treasurybegan producing penniesusing mostly zinc with acopper coating. Penniesminted after 1982 have adensity of 7.14 g/cm3.Check it out for yourself!

Density*Substance (g/cm3)

Helium (gas) 0.00001663

Oxygen (gas) 0.001331

Water (liquid) 1.00

Iron pyrite (solid) 5.02

Zinc (solid) 7.13

Density*Substance (g/cm3)

Copper (solid) 8.96

Silver (solid) 10.50

Lead (solid) 11.35

Mercury (liquid) 13.55

Gold (solid) 19.32

Figure 11 Did youfind gold or fool’s gold?

Density(g/cm3)

0.0001663

0.001331

1.00

5.02

7.13

Density(g/cm3)

8.96

10.50

11.35

13.55

19.32

* at 20!C and normal atmospheric pressure

Mass = 96.6 gVolume = 5.0 cm3

Densities of Common Substances*


The grease separator shown here isa kitchen device that cooks

use to collect the best meat juices for makinggravies. Based on what you know about density, describe how a grease separator works. Be sure to explain why the spout is at the bottom.

Liquid Layers What do you think causes the liquid inFigure 12 to look like it does? Is it magic? Is it trick photogra-phy? No, it’s differences in density! There are actually four dif-ferent liquids in the jar. Each liquid has a different density.Because of these differences in density, the liquids do not mixtogether but instead separate into layers, with the densest layeron the bottom and the least dense layer on top. The order inwhich the layers separate helps you determine how the den-sities of the liquids compare with one another.

The Density Challenge Imagine that you could put a lid onthe jar in the picture and shake up the liquids. Would the dif-ferent liquids mix together so that the four colors would blendinto one interesting color? Maybe for a minute or two. But ifthe liquids are not soluble in one another, they would startto separate, and eventually you’d end up with the same four layers.

The same thing happens when you mix oil and vinegar tomake salad dressing. But what do you think would happen ifyou added more oil? What if you added so much oil that therewas several times as much oil as there was vinegar? Surely theoil would get so heavy that it would sink below the vinegar,right? Wrong! No matter how much oil you have, it will alwaysbe less dense than the vinegar, so it will always rise to thetop. The same is true of the four liquids shown in Figure 12.Even if you add more yellow liquid than all of the other liquidscombined, all of the yellow liquid will rise to the top. That’sbecause density does not depend on how much of a substanceyou have.

Figure 12 The yellow liquid isthe least dense, and the greenliquid is the densest.

Chapter 246

REVIEW

1. List three physical prop-erties of water.

2. Why does a golf ball feelheavier than a table-tennisball?

3. Describe how you can deter-mine the relative densitiesof liquids.

4. Applying Concepts Howcould you determine thata coin is not pure silver?

Experiment for yourself with liquid layers on page 523 in

the LabBook.


Chemical PropertiesPhysical properties such as density, color, and mass are notthe only properties that describe matter. Chemical propertiesdescribe a substance based on its ability to change into a newsubstance with different properties. For example, a piece ofwood can be burned to create new substances (ash and smoke)with very different properties from the original piece of wood.Therefore, wood has the chemical property of flammability—the ability to burn. A substance that does not burn, such asgold, has the chemical property of nonflammability. Othercommon chemical properties include reactivity with oxygen,reactivity with acid, and reactivity with water. (The wordreactivity just means that when two substances get together,something can happen.)

Like physical properties, chemical properties can beobserved with your senses. However, chemical properties aren’tas easy to observe. For example, you can observe the flam-mability of wood only while the wood is burning. Likewise,you can observe the nonflammability of gold only when youtry to burn it and it won’t burn. But a substance always hasits chemical properties, even when you are not observing them.Therefore, a piece of wood is flammable even when it’s not burning.

Some Chemical Properties of Car Maintenance Look atthe old car shown in Figure 13. Its owner calls it Rust Bucket.Why has this car rusted so badly while some other cars thesame age remain in great shape? Knowing about chemicalproperties can help answer this question.

Most car bodies are made from steel, whichconsists mostly of iron. Iron has many favor-able physical properties, including strength,malleability, hardness, and a high meltingpoint. Iron also has many favorablechemical properties, including nonre-activity with oil and gasoline. All inall, steel is a good material to use forcar bodies. It’s not perfect, however,as you can probably tell from the carshown here.

Figure 13 Rust BucketOne unfavorable chemical property of iron is its reactivitywith oxygen. When iron isexposed to oxygen, it rusts. If left unprotected, the iron willeventually rust away.


This bumper is rust free because it is coated with an airtight barrierof chromium, which is nonreactivewith oxygen.

Paint doesn’t react withoxygen, so it provides abarrier between oxygen and the iron in the steel.

This hole started as a small chip in thepaint. The chipexposed the iron in the car’s body tooxygen. The ironrusted and eventuallycrumbled away.


Physical vs. Chemical PropertiesYou can describe matter by both physical and chemical prop-erties. The properties that are most useful in identifying a sub-

stance, such as density, solubility, and reactivity withacids, are its characteristic properties. The charac-

teristic properties of a substance are always the samewhether the sample you’re observing is large orsmall. Scientists rely on characteristic proper-ties to distinguish substances and to separatethem from one another. Figure 14 describessome physical and chemical properties.

It is important to remember the differencesbetween physical and chemical properties. You

can observe physical properties without chang-ing the identity of the substance. You can observe

chemical properties only in situations in which the iden-tity of the substance could change. The table below can helpyou understand the distinction between physical and chemi-cal properties.

Physical Changes Don’t Form New SubstancesA physical change is a change that affects one or more physi-cal properties of a substance. For example, if you were to breaka piece of chalk in two, you would be changing its physicalproperties of size and shape. But no matter how many timesyou break it, the chalk is still chalk. In other words, the chemi-cal properties of the chalk remain unchanged. Each piece ofchalk would still produce bubbles if you placed it in vinegar.

Chapter 248

Helium is used in airshipsbecause it is less dense thanair and is nonflammable.

If you add bleach to waterthat is mixed with red foodcoloring, the red color willdisappear.

Bending a bar of tin pro-duces a squealing soundknown as a tin cry.

Substance Physical property Chemical property

Helium less dense than air nonflammable

Wood grainy texture flammable

Baking soda white powder reacts with vinegar to produce bubbles

Powdered sugar white powder does not react with vinegar

Rubbing alcohol clear liquid flammable

Red food coloring red color reacts with bleach andloses color

Iron malleable reacts with oxygen

Tin malleable reacts with oxygen

Figure 14 Substances havedifferent physical and chemicalproperties.

a

b

Comparing Physical and Chemical Properties


Melting is another example of a physicalchange, as you can see in Figure 15. Still anotherphysical change occurs when a substance dis-solves into another substance. If you dissolvesugar in water, the sugar seems to disappearinto the water. But the identity ofthe sugar does not change. Ifyou taste the water, you willnotice that the sugar is stillthere. It has just undergone aphysical change. See the chartbelow for some more examplesof physical changes.

Can Physical Changes Be Undone? Because physicalchanges do not change the identity of substances, they areoften easy to undo. If you leave butter out on a warm counter,it will undergo a physical change—it will melt. Putting it backin the refrigerator will reverse this change by making it solidagain. Likewise, if you create a figure, such as a dragon or aperson, from a lump of clay, you drastically change the clay’sshape, causing a physical change. But because the identity ofthe clay does not change, you can crush your creation andform the clay back into the shape it was in before.

Chemical Changes Form New SubstancesA chemical change occurs when one or more substances arechanged into entirely new substances. The new substances havea different set of properties from the original substances.Chemical changes will or will not occur as described by thechemical properties of substances. But don’t confuse chemicalchanges with chemical properties—they are not the same thing.A chemical property describes a substance’s ability to gothrough a chemical change; a chemical change is the actualprocess in which that substance changes into another sub-stance. You can observe chemical properties only when a chemi-cal change might occur. Try the QuickLab on this page to learnmore about chemical changes.


! Freezing water for ice cubes

! Sanding a piece of wood

! Cutting your hair

! Crushing an aluminum can

! Bending a paper clip

! Mixing oil and vinegar

Changing Change1. Place a folded paper

towel in a small pieplate.

2. Pour vinegar intothe pie plate untilthe entire papertowel is damp.

3. Place two or three shinypennies on top of thepaper towel.

4. Put the pie plate in a placewhere it won’t be both-ered, and wait 24 hours.

5. Describe the chemicalchange that took place.

6. Write your observations inyour ScienceLog.

Figure 15 It took aphysical change to turna stick of butter into theliquid butter that makespopcorn so tasty, but theidentity of the butter didnot change.

More Examples of Physical Changes


Examples of Chemical Changes

A fun (and delicious) way to see what happens during chemi-cal changes is to bake a cake. When you bakea cake, you combine eggs, flour, sugar, but-ter, and other ingredients as shown inFigure 16. Each ingredient has its own setof properties. But if you mix themtogether and bake the batter in theoven, you get something com-pletely different. The heat ofthe oven and the interactionof the ingredients cause achemical change. As shownin Figure 17, you get a cakethat has completely differentproperties than any of theingredients. Some more exam-ples of chemical changes areshown below.

Figure 16 Each of these ingredi-ents has different physical andchemical properties.

The hot gas formed whenhydrogen and oxygen join tomake water helps blast thespace shuttle into orbit.

The Statue of Liberty is made of shiny, orange-brown copper.But the metal’s interaction withcarbon dioxide and water hasformed a new substance, coppercarbonate, and made this land-mark lady green over time.

Chapter 250

Figure 17 Chemical changes produce newsubstances with different properties.

Soured milk smells badbecause bacteria haveformed new substancesin the milk.

Effervescent tablets bubblewhen the citric acid and bakingsoda in them react in water.


Clues to Chemical Changes Look back at the bottom ofthe previous page. In each picture, there is at least one cluethat signals a chemical change. Can you find the clues? Here’sa hint: chemical changes often cause color changes, fizzing orfoaming, heat, or the production of sound, light, or odor.

In the cake example, you would probably smell the sweetaroma of the cake as it baked. If you looked into the oven,you would see the batter rise and turn brown. When you cutthe finished cake, you would see the spongy texture createdby gas bubbles that formed in the batter (if you baked it right,that is!). All of these yummy clues are signals of chemicalchanges. But are the clues and the chemical changes the samething? No, the clues just result from the chemical changes.

Can Chemical Changes Be Undone? Because new sub-stances are formed, you cannot reverse chemical changes usingphysical means. In other words, you can’t uncrumple or ironout a chemical change. Imagine trying to un-bake the cakeshown in Figure 18 by pulling out each ingredient.No way! Most of the chemical changes in your daily life, such as a cake baking ormilk turning sour, would be difficult to reverse. However, some chemicalchanges can be reversed under theright conditions by other chemi-cal changes. For example, the water formed in the spaceshuttle’s rockets could besplit back into hydrogenand oxygen using anelectric current.

1. Classify each of the following properties as either physi-cal or chemical: reacts with water, dissolves in acetone,is blue, does not react with hydrogen.

2. List three clues that a chemical change might be takingplace.

3. Comparing Concepts Describe the difference betweenphysical changes and chemical changes in terms of whathappens to the matter involved in each kind of change.


REVIEW

environmentalscienceC O N N E C T I O N

When fossil fuels are burned, achemical change takes placeinvolving sulfur (a substance infossil fuels) and oxygen (fromthe air). This chemical changeproduces sulfur dioxide, a gas.When sulfur dioxide enters theatmosphere, it undergoesanother chemical change byinteracting with water and oxygen. This chemical changeproduces sulfuric acid, a con-tributor to acid precipitation.Acid precipitation can kill treesand make ponds and lakesunable to support life.

Figure 18 Looking forthe original ingredi-

ents? You won’t findthem—their identitieshave changed.


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