CHAPTER 2 The Properties of Matter - Mrs. Erin · PDF file36 Chapter 2 NEW TERMS matter...

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

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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.


Chapter Highlights

Chapter 252

SECTION 1

Vocabularymatter (p. 36)volume (p. 36)meniscus (p. 37)mass (p. 38)gravity (p. 39)weight (p. 40)newton (p. 41)inertia (p. 42)

Section Notes• Matter is anything that has

volume and mass.

• Volume is the amount ofspace taken up by an object.

• The volume of liquids isexpressed in liters and milliliters.

• The volume of solid objectsis expressed in cubic units,such as cubic meters.

• Mass is the amount of matter in an object.

• Mass and weight are not thesame thing. Weight is a meas-ure of the gravitational forceon an object, usually in rela-tion to the Earth.

• Mass is usually expressed inmilligrams, grams, and kilograms.

• The newton is the SI unit offorce, so weight is expressedin newtons.

• Inertia is the tendency of allobjects to resist any changein motion. Mass is a measureof inertia. The more massivean object is, the greater itsinertia.

LabsVolumania! (p. 520)

Skills CheckMath ConceptsDENSITY To calculate an object’s density,divide the mass of the object by its volume. Forexample, the density of an object with a massof 45 g and a volume of 5.5 cm3 is calculated asfollows:

D ! "mV"

D ! "5.455cmg

3"

D ! 8.2 g/cm3

Visual UnderstandingMASS AND WEIGHTMass and weight arerelated, but they’re not thesame thing. Look back atFigure 8 on page 41 tolearn about the differencesbetween mass and weight.

PHYSICAL AND CHEMICAL PROPERTIES Allsubstances have physical and chemical proper-ties. You can compare some of those propertiesby reviewing the table on page 48.


53The Properties of Matter

SECTION 2

Vocabularyphysical property (p. 43)density (p. 44)chemical property (p. 47)physical change (p. 48)chemical change (p. 49)

Section Notes• Physical properties of matter

can be observed withoutchanging the identity of thematter.

• The density (mass per unitvolume) of a substance isalways the same at a givenpressure and temperatureregardless of the size of thesample of the substance.

• Chemical properties describea substance based on itsability to change into a newsubstance with differentproperties.

• Chemical properties can beobserved only when one sub-stance might become a newsubstance.

• The characteristic propertiesof a substance are always thesame whether the sampleobserved is large or small.

• When a substance undergoesa physical change, its iden-tity remains the same.

• A chemical change occurswhen one or more sub-stances are changed into new substances with dif-ferent properties.

LabsDetermining Density (p. 522)Layering Liquids (p. 523)White Before Your Eyes (p. 524)

Visit the National Science Teachers Association on-line Website for Internet resources related to this chapter. Just type inthe sciLINKS number for more information about the topic:

TOPIC: What Is Matter? sciLINKS NUMBER: HSTP030TOPIC: Describing Matter sciLINKS NUMBER: HSTP035TOPIC: Dark Matter sciLINKS NUMBER: HSTP040TOPIC: Building a Better Body sciLINKS NUMBER: HSTP045

Visit the HRW Web site for a variety oflearning tools related to this chapter. Just type in the keyword:

KEYWORD: HSTMAT

GO TO: go.hrw.com GO TO: www.scilinks.org


Chapter ReviewUSING VOCABULARY

For each pair of terms, explain the differencein their meanings.

1. mass/volume

2. mass/weight

3. inertia/mass

4. volume/density

5. physical property/chemical property

6. physical change/chemical change

UNDERSTANDING CONCEPTS

Multiple Choice

7. Which of these is not matter?a. a cloud c. sunshineb. your hair d. the sun

8. The mass of an elephant on the moonwould be a. less than its mass on Mars. b. more than its mass on Mars.c. the same as its weight on the moon.d. None of the above

9. Which of the following is not a chemicalproperty?a. reactivity with oxygenb. malleabilityc. flammabilityd. reactivity with acid

10. Your weight could beexpressed in which of thefollowing units?a. poundsb. newtonsc. kilogramsd. Both (a) and (b)

11. You accidentally break your pencil in half.This is an example ofa. a physical change.b. a chemical change.c. density.d. volume.

12. Which of the following statements aboutdensity is true?a. Density depends on mass and volume.b. Density is weight per unit volume.c. Density is measured in milliliters.d. Density is a chemical property.

13. Which of the following pairs of objectswould have the greatest attraction towardeach other due to gravity?a. a 10 kg object and a 10 kg object,

4 m apart b. a 5 kg object and a 5 kg object,

4 m apart c. a 10 kg object and a 10 kg object,

2 m apartd. a 5 kg object and a 5 kg object,

2 m apart

14. Inertia increases as ? increases. a. time c. massb. length d. volume

Short Answer

15. In one or two sentences, explain the dif-ferent processes in measuring the volumeof a liquid and measuring the volume of a solid.

16. In one or two sentences,explain the relationshipbetween mass and inertia.

17. What is the formula forcalculating density?

18. List three characteristicproperties of matter.

54 Chapter 2Copyright © by Holt, Rinehart and Winston. All rights reserved.

Concept Mapping

19. Use the followingterms to create aconcept map: matter,mass, inertia, vol-ume, milliliters,cubic centimeters,weight, gravity.

CRITICAL THINKING AND PROBLEM SOLVING

20. You are making breakfast for your pickyfriend, Filbert. You make him scrambledeggs. He asks, “Would you please takethese eggs back to the kitchen and poachthem?” What scientific reason do yougive Filbert for not changing his eggs?

21. You look out your bedroom window andsee your new neighbors moving in. Yourneighbor bends over to pick up a smallcardboard box, but he cannot lift it. Whatcan you conclude about the item(s) in thebox? Use the terms mass and inertia toexplain how you came to this conclusion.

22. You may sometimes hear on the radio oron television that astronauts are “weight-less” in space. Explain why this is nottrue.

23. People commonly use the term volume todescribe the capacity of a container. Howdoes this definition of volume differ fromthe scientific definition?

MATH IN SCIENCE

24. What is the volume of a book with thefollowing dimensions: a width of 10 cm, alength that is two times the width, and aheight that is half the width? Rememberto express your answer in cubic units.

25. A jar contains 30 mL of glycerin (mass =37.8 g) and 60 mL of corn syrup (mass =82.8 g). Which liquid is on top? Showyour work, and explain your answer.

INTERPRETING GRAPHICS

Examine the photograph below, and answerthe following questions:

26. List three physical properties of this can.

27. Did a chemical change or a physicalchange cause the change in this can’sappearance?

28. How does the density of the metal in thecan compare before and after the change?

29. Can you tell what the chemical propertiesof the can are just by looking at the pic-ture? Explain.


Take a minute to review your answers tothe ScienceLog questions on page 35.Have your answers changed? If neces-sary, revise your answers based on whatyou have learned since you began thischapter.

Poach these,please!


P H Y S I C A L S C I E N C E • A S T R O N O M Y

In the Dark About Dark Matter

56

What is the universe made of?Believe it or not, whenastronomers try to answer thisquestion, they still find them-selves in the dark. Surprisingly,there is more to the universethan meets the eye.

A Matter of GravityAstronomers noticed some-thing odd when studying themotions of galaxies in space.They expected to find a lot ofmass in the galaxies. Instead,they discovered that the massof the galaxies was not greatenough to explain the large gravitational forcecausing the galaxies’ rapid rotation. So whatwas causing the additional gravitational force?Some scientists think the universe containsmatter that we cannot see with our eyes or ourtelescopes. Astronomers call this invisible mat-ter dark matter.

Dark matter doesn’t reveal itself by givingoff any kind of electromagnetic radiation, suchas visible light, radio waves, or gamma radia-tion. According to scientific calculations, darkmatter could account for between 90 and 99percent of the total mass of the universe! Whatis dark matter? Would you believe MACHOs and WIMPs?

MACHOsScientists recently proved the existence ofMAssive Compact Halo Objects (MACHOs) inour Milky Way galaxy by measuring their gravi-tational effects. Even though scientists knowMACHOs exist, they aren’t sure what MACHOsare made of. Scientists suggest that MACHOsmay be brown dwarfs, old white dwarfs, neu-tron stars, or black holes. Others suggest they

are some type of strange, newobject whose properties stillremain unknown. Even thoughthe number of MACHOs isapparently very great, they stilldo not represent enough miss-ing mass. So scientists offeranother candidate for darkmatter—WIMPs.

WIMPsTheories predict that WeaklyInteracting Massive Particles(WIMPs) exist, but scientistshave never detected them.WIMPs are thought to be mas-

sive elementary particles that do not interactstrongly with matter (which is why scientistshave not found them).

More Answers NeededSo far, evidence supports the existence ofMACHOs, but there is little or no solid evidenceof WIMPs or any other form of dark matter.Scientists who support the idea of WIMPs areconducting studies of the particles that makeup matter to see if they can detect WIMPs.Other theories are that gravity acts differentlyaround galaxies or that the universe is filledwith things called “cosmic strings.” Scientistsadmit they have a lot of work to do before theywill be able to describe the universe—and allthe matter in it.

On Your Own! What is microlensing, and what does it haveto do with MACHOs? How might the neutrinoprovide valuable information to scientists whoare interested in proving the existence ofWIMPs? Find out on your own!

" The Large MagellanicCloud, located 180,000light-years from Earth


57

Have you ever broken anarm or a leg? If so, youprobably wore a cast

while the bone healed. Butwhat happens when a bone istoo badly damaged to heal? Insome cases, a false bone madefrom a metal called titaniumcan take the original bone’splace. Could using titaniumbone implants be the first stepin creating bionic body parts?Think about it as you readabout some of titanium’samazing properties.

Imitating the OriginalWhy would a metal like titanium be used toimitate natural bone? Well, it turns out that atitanium implant passes some key tests forbone replacement. First of all, real bones areincredibly lightweight and sturdy, and healthybones last for many years. Therefore, a bone-replacement material has to be lightweight butalso very durable. Titanium passes this testbecause it is well known for its strength, and it is also lightweight.

Second, the human body’s immune systemis always on the lookout for foreign substances.If a doctor puts a false bone in place and thepatient’s immune system attacks it, an infectioncan result. Somehow, the false bone must beable to chemically trick the body into thinkingthat the bone is real. Does titanium pass thistest? Keep reading!

Accepting ImitationBy studying the human body’s immune system,scientists found that the body accepts certainmetals. The body almost always accepts onemetal in particular. Yep, you guessed it—tita-nium! This turned out to be quite a discovery.

Doctors could implant pieces oftitanium into a person’s bodywithout triggering an immunereaction. A bond can even formbetween titanium and existingbone tissue, fusing the bone tothe metal!

Titanium is shaping up tobe a great bone-replacementmaterial. It is lightweight andstrong, is accepted by the body,can attach to existing bone,and resists chemical changes,such as corrosion. But scientistshave encountered a slight prob-lem. Friction can wear away

titanium bones, especially those used near thehips and elbows.

Real SuccessAn unexpected surprise, not from the field ofmedicine but from the field of nuclear physics,may have solved the problem. Researchershave learned that by implanting a special formof nitrogen on the surface of a piece ofmetal, they can create a surface layer onthe metal that is especially durable andwear resistant. When this form of nitrogenis implanted in titanium bones, the bonesretain all the properties of pure titaniumbones but also become very wear resistant.The new bones should last through decadesof heavy use without needing to be replaced.

Think About It! What will the future hold? As time goes by, doctors become more successful atimplanting titanium bones. What do youthink would happen if the titanium boneswere to eventually become better than real bones?

Building a Better Body

" Titanium bones—evenbetter than the real thing?


You are jogging along an ocean beach. Animmense black storm cloud forms a shortdistance ahead. Suddenly there is a blind-ing flash of light followed by an explo-sion of thunder.

As the storm moves inland, you con-tinue your jog. A short time later, youarrive at the section of beach where thestorm passed. You notice an odd mark inthe sand. You dig into the sand and find anobject like the one shown below. You won-der what this object could be.

Lightning sometimes leaves behind astrange calling card known as a fulgurite(FUHL gyoo RIET). A fulgurite is a rare typeof natural glass that is sometimes formedwhen lightning strikes silica, a mineral oftenfound in soil or sand. Producing a tempera-ture equal to that of the sun’s surface(33,000°C), lightning melts solid silica intoliquid. The silica then cools and hardens tobecome glass. The transformation of thesilica from a solid to a liquid andback to a solid happens in theblink of an eye!

The physical changes thatoccur in the manufacture ofglass are identical to thosethat occur when a fulguriteis created. The process,however, is very different.

Chapter 358

CH

AP

TE

R

3Imagine . . .

States of Matter


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

1. What are the four most familiar statesof matter?

2. Compare the motion of the particlesin a solid, a liquid, and a gas.

3. Name three ways matter changesfrom one state to another.

59

Instead of lightning, glass makers use alarge oven to heat the silica and other ingre-dients. Once this mixture becomes a liquid,it is removed from the oven and formed intoa desired shape. The shaping process musthappen quickly, before the liquid glassfreezes into solid. By controlling the physi-cal change between liquid glass and solidglass, known as a change of state, glass mak-ers create the windows, light bulbs, and bot-tles you use every day. Read on to discovermore about the states of matter.

Vanishing ActIn this activity, you will use rubbing alcohol toinvestigate a change of state.

Procedure1. Pour rubbing alcohol into a small plastic cup

until it just covers the bottom of the cup.

2. Moisten the tip of a cotton swab by dipping itinto the alcohol in the cup.

3. Rub the cotton swab on the palm of your hand.

4. Record your observations in your ScienceLog.

5. Wash your hands thoroughly.

Analysis6. Explain what happened to the alcohol.

7. Did you feel a sensation of hot or cold? If so,how do you explain what you observed?

8. Record your answers in your ScienceLog.


Chapter 360

N E W T E R M Sstates of matter pressuresolid Boyle’s lawliquid Charles’s lawgas plasma

O B J E CT I V E S! Describe the properties shared

by particles of all matter.! Describe the four states of mat-

ter discussed here.! Describe the differences

between the states of matter.! Predict how a change in pres-

sure or temperature will affectthe volume of a gas.

Section1 Four States

of MatterFigure 1 shows a model of theearliest known steam engine,invented about A.D. 60 byHero, a scientist who lived inAlexandria, Egypt. This modelalso demonstrates the fourmost familiar states of matter:solid, liquid, gas, and plasma.The states of matter are thephysical forms in which a sub-stance can exist. For example,water commonly exists inthree different states of mat-ter: solid (ice), liquid (water),and gas (steam).

Moving Particles Make Up All MatterMatter consists of tiny particles called atoms and molecules(MAHL i KYOOLZ) that are too small to see without an amazinglypowerful microscope. These atoms and molecules are always inmotion and are constantly bumping into one another. The stateof matter of a substance is determined by how fast the particlesmove and how strongly the particles are attracted to one another.Figure 2 illustrates three of the states of matter—solid, liquid,and gas—in terms of the speed and attraction of the particles.

Figure 1 This model of Hero’ssteam engine spins as steamescapes through the nozzles.

Particles of a solid do not movefast enough to overcome thestrong attraction between them,so they are held tightly in place.The particles vibrate in place.

Particles of a liquid move fastenough to overcome some ofthe attraction between them.The particles are able to slidepast one another.

Particles of a gas move fastenough to overcome nearly allof the attraction between them.The particles move indepen-dently of one another.

Figure 2 Models of a Solid, a Liquid, and a Gas

Gas

Solid

Liquid

Plasma


Figure 4 Differing arrangements of particles in crys-talline solids and amorphous solids lead to differentproperties. Imagine trying to hit a home run with arubber bat!

Solids Have Definite Shape and VolumeLook at the ship in Figure 3. Even though it is in a bottle, itkeeps its original shape and volume. If you moved it to a largerbottle, the shape and volume of the ship would not change.Scientifically, the state in which matter has adefinite shape and volume is solid. Because theparticles of a substance in the solid state arevery close together, the attraction betweenthem is stronger than the attraction betweenthe particles of the same substance in the liquid or gaseousstate. The atoms or molecules in a solid are still moving, butthey do not move fast enough to overcome the attractionbetween them. Each particle vibrates in place because it islocked in position by the particles around it.

Two Types of Solids Solids are often divided into two cat-egories—crystalline and amorphous (uh MOHR fuhs). Crystallinesolids have a very orderly, three-dimensional arrangement ofatoms or molecules. The particles are arranged much like theseats in a movie theater. That is, the particles are in a repeat-ing pattern of rows. Examples of crystalline solids include iron,diamond, and ice. Amorphous solids are composed of atomsor molecules that are in no particular order. The particles inan amorphous solid are arranged like people attending a con-cert in a park. That is, each particle is in a particular spot, butthe particles are in no particular pattern. Examples of amor-phous solids include rubber and wax. Figure 4 illustrates thedifferences in the arrangement of particles in these two solids.

States of Matter 61

The particles in anamorphous solid donot have an orderlyarrangement.

The particles in acrystalline solidhave a very orderlyarrangement.

Imagine that you are a parti-cle in a solid. Your position inthe solid is your chair. In yourScienceLog, describe the dif-ferent types of motion thatare possible even though youcannot leave your chair.

Figure 3 Because this ship is asolid, it does not take the shapeof the bottle.


Liquids Change Shape but Not VolumeYou already know from your own experience that a liquid will

conform to the shape of whatever container it is putin. You are reminded of this every time you pour

yourself a glass of juice. The state in which mattertakes the shape of its container but has a defi-nite volume is liquid. The atoms or moleculesin liquids move fast enough to overcomesome of the attractions between them. Theparticles slide past each other until the liquidtakes the shape of its container. Figure 5shows how the particles in juice might look

if they were large enough to see.Even though liquids change shape, they do

not readily change volume. You have also experi-enced this for yourself. You know that a can of soda

contains a certain volume of liquid regardless of whether youpour it into a large container or a small one. Figure 6 illustratesthis point using a beaker and a graduated cylinder.

Because the particles in liquids are close to one another, itis difficult to push them closer together. This makes liquidsideal for use in hydraulic (hie DRAW lik) systems to do work.For example, brake fluid is the liquid used in the brake sys-tems of cars. Stepping on the brake pedal applies a force to theliquid. It is easier for the particles in the liquid to move awayrather than to be squeezed closer together. Therefore, the fluidpushes the brake pads outward against the wheels. The forceof the brake pads pushing against the wheels slows the car.

Chapter 362

The Boeing 767 Freighter, atype of commercial airliner,has 187 km (116 mi) ofhydraulic tubing.

Figure 6 Even when liquidschange shape, they don’t changevolume.

Figure 5 Particles in a liquidslide past one another untilthe liquid conforms to theshape of its container.


Two Properties of Liquids Two other important propertiesof liquids are surface tension and viscosity (vis KAHS uh tee).Surface tension is the force acting on the particles at the sur-face of a liquid that causes the liquid to form spherical drops,as shown in Figure 7. Different liquids have different surfacetensions. For example, rubbing alcohol has a lower surface tension than water, but mercury has a higher surface tensionthan water.

Viscosity is a liquid’s resistance to flow. In general, thestronger the attractions between a liquid’s particles are, themore viscous the liquid is. Think of the difference betweenpouring honey and pouring water. Honey flows more slowlythan water because it has a higher viscosity than water.

Gases Change Both Shape and VolumeThe last time you saw balloons being filled with helium gas,did you wonder how many balloons could be filled from asingle metal cylinder of helium? The number may surpriseyou. One cylinder can fill approximately 700 balloons. Howis this possible? After all, the volume of the metal cylinderis equal to the volume of only about fiveinflated balloons.

To answer this question, you mustknow that the state in which matterchanges in both shape and volume isgas. The atoms or molecules in a gasmove fast enough to break away com-pletely from one another. Therefore, theparticles of a substance in the gaseous statehave less attraction between them than par-ticles of the same substance in the solid or liquidstate. The particles move independently of oneanother, colliding frequently with one anotherand with the inside of the container as theyspread out. So in a gas, there is empty spacebetween particles.

The amount of empty space in a gas canchange. For example, the helium in the metalcylinder consists of atoms that have been forced veryclose together, as shown in Figure 8. As the helium fills theballoon, the atoms spread out, and the amount of empty spacein the gas increases. As you continue reading, you will learnhow this empty space is related to pressure.

63

Figure 8 The particles of the gas in thecylinder are much closer together thanthe particles of the gas in the balloons.

Figure 7 Liquids formspherical drops as a resultof surface tension.


Gas Under PressurePressure is the amount of force exerted on a given area. Youcan think of this as the number of collisions of particles againstthe inside of the container. Compare the basketball with thebeach ball in Figure 9. The balls have the same volume andcontain particles of gas (air) that constantly collide with oneanother and with the inside surface of the balls. Notice, how-ever, that there are more particles in the basketball than inthe beach ball. As a result, more particles collide with theinside surface of the basketball than with the inside surface ofthe beach ball. When the number of collisions increases, theforce on the inside surface of the ball increases. This increasedforce leads to increased pressure.

Chapter 364

Figure 9 Both balls shown here are full of air, but the pressure inthe basketball is higher than the pressure in the beach ball.

1. List two properties that all particles of matter have incommon.

2. Describe solids, liquids, and gases in terms of shape andvolume.

3. Why can the volume of a gas change?

4. Applying Concepts Explain why you would pump upa flat basketball.

The beach ball has a lower pressurethan the basketball because the lessernumber of particles of gas are fartherapart. Therefore, they collide with theinside of the ball at a slower rate.

The basketball has a higher pressurethan the beach ball because the greaternumber of particles of gas are closertogether. Therefore, they collide withthe inside of the ball at a faster rate.

REVIEW

Self-CheckHow would an increasein the speed of theparticles affect thepressure of gas in ametal cylinder? (Seepage 596 to check youranswer.)


Laws Describe Gas BehaviorEarlier in this chapter, you learned about the atoms and mol-ecules in both solids and liquids. You learned that comparedwith gas particles, the particles of solids and liquids are closelypacked together. As a result, solids and liquids do not changevolume very much. Gases, on the other hand, behave differ-ently; their volume can change by a large amount.

It is easy to measure the volume of a solid or liquid, buthow do you measure the volume of a gas? Isn’t the volume ofa gas the same as the volume of its container? The answer isyes, but there are other factors, such as pressure, to consider.

Boyle’s Law Imagine a diver at a depth of 10 m blowing abubble of air. As the bubble rises, its volume increases. By thetime the bubble reaches the surface, its original volume willhave doubled due to the decrease in pressure. The relation-ship between the volume and pressure of a gas is known asBoyle's law because it was first described by Robert Boyle, aseventeenth-century Irish chemist. Boyle’s law states that fora fixed amount of gas at a constant temperature, the volumeof a gas increases as its pressure decreases. Likewise, the vol-ume of a gas decreases as its pressure increases. Boyle’s law isillustrated by the model in Figure 10.

States of Matter 65

Releasing the plunger allowsthe gas to change to an inter-mediate volume and pressure.

Pushing the plunger downincreases the pressure of thegas. The particles of gas collidemore often with the walls ofthe piston as they are forcedcloser together. The volume ofthe gas decreases as thepressure increases.

Lifting the plunger decreasesthe pressure of the gas. Theparticles of gas collide lessoften with the walls of the piston as they spread fartherapart. The volume of the gasincreases as the pressuredecreases.

Figure 10 Boyle’s LawEach illustration shows the same piston and thesame amount of gas at the same temperature.


Weather balloons demonstrate a practical use of Boyle’slaw. A weather balloon carries equipment into the atmosphereto collect information used to predict the weather. This balloonis filled with only a small amount of gas because the pressureof the gas decreases and the volume increases as the balloonrises. If the balloon were filled with too much gas, it wouldpop as the volume of the gas increased.

Charles’s Law An inflated balloon will also pop when it getstoo hot, demonstrating another gas law—Charles’s law.Charles’s law states that for a fixed amount of gas at a con-stant pressure, the volume of the gas increases as its tempera-ture increases. Likewise, the volume of the gas decreases as itstemperature decreases. Charles’s law is illustrated by the modelin Figure 11. You can see Charles’s law in action by puttingan inflated balloon in the freezer. Wait about 10 minutes, andsee what happens!

Chapter 366

Lowering the temperature ofthe gas causes the particlesto move more slowly. Theyhit the sides of the pistonless often and with lessforce. As a result, theplunger enters the pistonand the volume of the gasdecreases.

Raising the temperature ofthe gas causes the particlesto move more quickly. Theyhit the sides of the pistonmore often and with greaterforce. As a result, theplunger is pushed upwardand the volume of the gasincreases.

Figure 11 Charles’s LawEach illustration shows the same piston and thesame amount of gas at the same pressure.Gas Law Graphs

Each graph below illustratesa gas law. However, the vari-able on one axis of eachgraph is not labeled. Answerthe following questions foreach graph:1. As the volume increases,

what happens to the miss-ing variable?

2. Which gas law is shown? 3. What label belongs on the

axis?4. Is the graph linear or non-

linear? What does this tellyou?

MATH BREAK

Graph A

Graph B

?

Volu

me

?

Volu

me

See Charles’s law in action foryourself using a balloon

on page 526 of theLabBook.


PlasmasThe sun and other stars are made of the most common stateof matter in the universe, called plasma. Plasma is the state ofmatter that does not have a definite shape or volume andwhose particles have broken apart.

Plasmas have some properties that are quite different fromthe properties of gases. Plasmas conduct electric current, whilegases do not. Electric and magnetic fields affect plasmas butdo not affect gases. In fact, strong magnets are used to form a magnetic “bottle” to contain very hot plasmas that woulddestroy any other container.

Here on Earth, natural plasmasare found in lightning and fire.The incredible light show inFigure 12, called the aurora bore-alis (ah ROHR uh BOHR ee AL is),is a result of plasma from the suncausing gas particles in the upperatmosphere to glow. Artificial plas-mas, found in fluorescent lightsand plasma balls, are created bypassing electric charges throughgases.

States of Matter 67

1. When scientists record the volume of a gas, why do theyalso record the temperature and the pressure?

2. List two differences between gases and plasmas.

3. Applying Concepts What happens to the volume of aballoon left on a sunny windowsill? Explain.

Figure 12 Auroras, like theaurora borealis seen here, formwhen high-energy plasma col-lides with gas particles in theupper atmosphere.

Even though plasmas arerare on Earth, more than 99percent of the known matterin the universe is in theplasma state.

One of your friends overin-flated the tires on her bicycle.

Use Charles’s law to explain whyshe should let out some of the airbefore going for a ride on a hot day.

REVIEW


Chapter 3

N E W T E R M Schange of state vaporizationmelting evaporationendothermic boilingfreezing condensationexothermic sublimation

O B J E CT I V E S! Describe how substances change

from state to state.! Explain the difference between

an exothermic change and anendothermic change.

! Compare the changes of state.

Section2 Changes of State

A change of state is the conversion of a substance from onephysical form to another. All changes of state are physicalchanges. In a physical change, the identity of a substance doesnot change. In Figure 13, the ice, liquid water, and steam areall the same substance, water. In this section, you will learnabout the four changes of state illustrated in Figure 13 as wellas a fifth change of state called sublimation (SUHB li MAY shuhn).

During a change of state, the energy of a substance changes.The energy of a substance is related to the motion of the par-ticles of the substance. For example, the molecules in the liq-uid water in Figure 13 move faster than the molecules in theice. Therefore, the liquid water has more energy than the ice.

If energy is added to a substance, the particles of the sub-stance move faster. If energy is removed from a substance, theparticles of the substance move slower. The temperature of asubstance is a measure of the speed of the particles and there-fore is a measure of the energy of a substance. For example,the steam shown above has a higher temperature than the liq-uid water, so the particles in the steam have more energy thanthe particles in the liquid water. A transfer of energy, knownas heat, causes the temperature of a substance to change, whichcan lead to a change of state.

Freezing

Vapo

riza

tion

Melting

Cond

ensa

tion

Figure 13 The terms in the arrows arechanges of state. Water commonly goesthrough the changes of state shown here.

Want to learn how to get

power fromchanges ofstate? Steam

ahead topage 79.

68Copyright © by Holt, Rinehart and Winston. All rights reserved.

Melting: Solids to LiquidsMelting is the change of state from a solid to a liquid. This iswhat happens when an ice cube melts. Figure 14 shows a metalcalled gallium melting. What is unusual about this metal isthat it melts at around 30°C. Because your normal body tem-perature is about 37°C, gallium would reach its melting pointright in your hand!

The melting point of a substance is simply the temperatureat which the substance changes from a solid to a liquid. Themelting points of substances vary widely. As you know, themelting point of gallium is 30°C. Common table salt, how-ever, has a melting point of 801°C.

Most substances have a unique melting point. Melting pointcan be used with other data to identify a substance. Becausethe melting point does not change with different amounts ofthe substance, the melting point is considered a characteristicproperty of a substance.

For a solid to melt, the particles must overcome some oftheir attractions to other particles. When a solid is at its melt-ing point, any energy it absorbs increases the motion of theatoms or molecules until some of them overcome the attrac-tions that hold them in place. Melting is an endothermic changebecause energy is absorbed, or taken in, by the substance asit changes state.

Freezing: Liquids to SolidsFreezing is the change of state from aliquid to a solid. The temperature atwhich a liquid changes into a solid isits freezing point. Freezing is the reverseprocess of melting, so freezing and melt-ing occur at the same temperature, asshown in Figure 15.

For a liquid to freeze, the motion ofthe atoms or molecules must slow tothe point where attractions betweenthem overcome the motion. The parti-cles are pulled into a more orderedarrangement. When a liquid is at itsfreezing point, removing energy causesthe particles to begin locking into place.Freezing is an exothermic change be-cause energy is removed from, or takenout of, the substance as it changes state.

States of Matter 69

Figure 14 Even though galliumis a metal, it would not be veryuseful as jewelry!

FPO

Figure 15 Liquidwater freezes at thesame temperaturethat ice melts—0°C.

If energy is added at 0°C, the ice willmelt.

If energy is removedat 0°C, the liquidwater will freeze.


Vaporization: Liquids to GasesOne way to experience vaporization (VAY puhr i ZAY shuhn) isto iron a shirt—carefully!—using a steam iron. You will noticesteam coming up from the iron as the wrinkles are eliminated.

This steam results from the vaporization of liquid water bythe iron. Vaporization is simply the change of state froma liquid to a gas.

Boiling is vaporization that occurs throughout a liquid.The temperature at which a liquid boils is called its boilingpoint. Like the melting point, the boiling point is a char-acteristic property of a substance. The boiling point of wateris 100°C, whereas the boiling point of liquid mercury is357°C. Figure 16 illustrates the process of boiling and a sec-

ond form of vaporization, evaporation (ee VAP uh RAY shuhn).Evaporation is vaporization that occurs at the surface of a

liquid below its boiling point, as shown in Figure 16. Whenyou perspire, your body is cooled through the process of evapo-ration. Perspiration is mostly water. Water absorbs energy fromyour skin as it evaporates. You feel cooler because your bodytransfers energy through heat to the water. Evaporation alsoexplains why water in a glass placed on a table disappears afterseveral days.

Chapter 370

Figure 16 Both boilingand evaporation changea liquid to a gas.

Self-CheckIs vaporization anendothermic orexothermic change?(See page 596 to checkyour answer.)

Boilingpoint

Boilingpoint

Boiling occurs in a liquid at its boiling point.As energy is added to the liquid, particlesthroughout the liquid move fast enough tobreak away from the particles around themand become a gas.

Evaporation occurs in a liquid belowits boiling point. Some particles at thesurface of the liquid move fast enoughto break away from the particlesaround them and become a gas.


Pressure Affects Boiling Point Earlier you learned that waterboils at 100!C. In fact, water only boils at 100!C at sea level,where the atmospheric pressure is 101,000 Pa. A pascal (Pa) issimply the SI unit for pressure. It is a force of 1 N exerted overan area of 1 m2. Atmospheric pressure is caused by the weightof the gases that make up the atmosphere. Atmospheric pres-sure varies depending on where you are in relation to sea levelbecause the higher you go above sea level, the less air there isabove you. The atmospheric pressure is lower at higher eleva-tions. If you were to boil water at the top of a mountain, theboiling point would be lower than 100!C. For example, Denver,Colorado, is 1.6 km (1 mi) above sea level. Water boils inDenver at about 95!C. You can make water boil at an evenlower temperature by doing the QuickLab at right.

Condensation: Gases to LiquidsLook at the cool glass of lemonade in Figure 17. Notice thebeads of water on the outside of the glass. These form asa result of condensation. Condensation is the change ofstate from a gas to a liquid. The condensation point of asubstance is the temperature at which the gas becomes aliquid and is the same temperature as the boiling point ata given pressure. Thus, at sea level, steam condenses to form water at 100!C—the same temperature at which water boils.

For a gas to become a liquid,large numbers of atoms or mol-ecules must clump together.Particles clump together whenthe attraction between themovercomes their motion. For thisto occur, energy must be re-moved from the gas to slow the particles down. Therefore,condensation is an exothermicchange.

71

Boiling Water Is Cool1. Remove the cap

from a syringe.

2. Place the tip of thesyringe in the warmwater provided byyour teacher. Pull theplunger out until you have10 mL of water in thesyringe.

3. Tightly cap the syringe.

4. Hold the syringe, andslowly pull the plunger out.

5. Observe any changes yousee in the water. Recordyour observations in yourScienceLog.

6. Why are you not burned bythe boiling water in thesyringe?

States of Matter

Figure 17 Gaseous water inthe air will become liquid whenit contacts a cool surface.

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

The amount of gaseous waterthat air can hold decreases asthe temperature of the airdecreases. As the air cools,some of the gaseous watercondenses to form smalldrops of liquid water. Thesedrops form clouds in the skyand fog near the ground.


Sublimation: Solids Directly to GasesLook at the solids shown in Figure 18. The solid on the left isice. Notice the drops of liquid collecting as it melts. On theright, you see carbon dioxide in the solid state, also called dryice. It is called dry ice because instead of melting into a liquid,

it goes through a change of state called subli-mation. Sublimation is the change of state froma solid directly into a gas. Dry ice is colder thanice, and it doesn't melt into a puddle of liquid.It is often used to keep food, medicine, and othermaterials cold without getting them wet.

For a solid to change directly into a gas, theatoms or molecules must move from being verytightly packed to being very spread apart. The attrac-tions between the particles must be completely over-come. Because this requires the addition of energy,sublimation is an endothermic change.

Comparing Changes of StateAs you learned in Section 1 of this chapter, the state of a sub-stance depends on how fast its atoms or molecules move andhow strongly they are attracted to each other. A substance mayundergo a physical change from one state to another by anendothermic change (if energy is added) or an exothermicchange (if energy is removed). The table below shows the dif-ferences between the changes of state discussed in this section.

Chapter 372

Summarizing the Changes of State

Endothermic orexothermic?

Ice melts into liquid water at 0!C.

Liquid water freezes into ice at 0!C.

Liquid water vaporizes into steam at 100!C.

Steam condenses into liquid water at 100!C.

Solid dry ice sublimes into a gas at –78!C.

Melting solid liquid endothermic

Freezing liquid solid exothermic

Vaporization liquid gas endothermic

Condensation gas liquid exothermic

Sublimation solid gas endothermic

Change of state Direction Example

!

!

!

!

!

Figure 18 Ice melts, but dry ice, on the right, turnsdirectly into a gas.


Temperature Change Versus Change of StateWhen most substances lose or absorb energy, one of two thingshappens to the substance: its temperature changes or its statechanges. Earlier in the chapter, you learned that the temper-ature of a substance is a measure of the speed of the particles.This means that when the temperature of a substance changes,the speed of the particles also changes. But while a substancechanges state, its temperature does not change until the changeof state is complete, as shown in Figure 19.

States of Matter 73

Boiling point

Melting point

Time

Tem

pera

ture

( C

)

100

0

o

ENER

GY

ADDED ENER

GY ADDED

ENER

GY ADDED ENERGY

ADDE

D

1. Compare endothermic and exothermic changes.

2. Classify each change of state (melting, freezing, vapor-ization, condensation, and sublimation) as endothermicor exothermic.

3. Describe how the motion and arrangement of particleschange as a substance freezes.

4. Comparing Concepts How are evaporation and boilingdifferent? How are they similar?

REVIEW

Figure 19 Changing the State of Water

Temperature remains atthe melting point until allof the solid has melted.

Temperature remains atthe boiling point until allof the liquid has boiled.


Chapter Highlights

Chapter 374

SECTION 1

Vocabularystates of matter (p. 60)solid (p. 61)liquid (p. 62)gas (p. 63)pressure (p. 64)Boyle’s law (p. 65)Charles’s law (p. 66)plasma (p. 67)

Section Notes• The states of matter are the

physical forms in which asubstance can exist. The fourmost familiar states are solid,liquid, gas, and plasma.

• All matter is made of tinyparticles called atoms andmolecules that attract eachother and move constantly.

• A solid has a definite shapeand volume.

• A liquid has a definitevolume but not a definiteshape.

• A gas does not have adefinite shape or volume. A gas takes the shape andvolume of its container.

• Pressure is a force per unitarea. Gas pressure increasesas the number of collisionsof gas particles increases.

• Boyle’s law states that thevolume of a gas increases asthe pressure decreases if thetemperature does notchange.

• Charles’s law states that thevolume of a gas increases asthe temperature increases if the pressure does notchange.

• Plasmas are composed ofparticles that have brokenapart. Plasmas do not have a definite shape or volume.

LabsFull of Hot Air! (p. 526)

Skills CheckMath ConceptsGRAPHING DATA The relation-ship between measured valuescan be seen by plotting the dataon a graph. The top graph showsthe linear relationship describedby Charles’s law—as the tempera-ture of a gas increases, its volumeincreases. The bottom graphshows the nonlinear relationshipdescribed by Boyle’s law—as thepressure of a gas increases, its volume decreases.

Visual UnderstandingPARTICLE ARRANGEMENT Many of theproperties of solids, liquids, and gases are dueto the arrangement of the atoms or moleculesof the substance. Review the models in Figure 2on page 60 to study the differences in particlearrangement between the solid, liquid, andgaseous states.

SUMMARY OF THE CHANGES OF STATEReview the table on page 72 to study the direc-tion of each change of state and whether energyis absorbed or removed during each change.

Temperature

Volu

me

Pressure

Volu

me


75States of Matter

SECTION 2

Vocabularychange of state (p. 68)melting (p. 69)endothermic (p. 69)freezing (p. 69)exothermic (p. 69)vaporization (p. 70)boiling (p. 70)evaporation (p. 70)condensation (p. 71)sublimation (p. 72)

Section Notes• A change of state is the con-

version of a substance fromone physical form to an-other. All changes of state are physical changes.

• Exothermic changes releaseenergy. Endothermic changesabsorb energy.

• Melting changes a solid to aliquid. Freezing changes aliquid to a solid. The freez-ing point and melting pointof a substance are the sametemperature.

• Vaporization changes aliquid to a gas. Boiling occursthroughout a liquid at theboiling point. Evaporationoccurs at the surface of aliquid, at a temperaturebelow the boiling point.

• Condensation changes a gas to a liquid.

• Sublimation changes a solid directly to a gas.

• Temperature does not change during a change of state.

LabsCan Crusher (p. 527)A Hot and Cool Lab (p. 528)


TOPIC: Forms and Uses of Glass sciLINKS NUMBER: HSTP055TOPIC: Solids, Liquids, and Gases sciLINKS NUMBER: HSTP060TOPIC: Natural and Artificial Plasma sciLINKS NUMBER: HSTP065TOPIC: Changes of State sciLINKS NUMBER: HSTP070TOPIC: The Steam Engine sciLINKS NUMBER: HSTP075


KEYWORD: HSTSTA



Chapter ReviewUSING VOCABULARY

For each pair of terms, explain the differencein meaning.

1. exothermic/endothermic

2. Boyle’s Law/Charles’s Law

3. evaporation/boiling

4. melting/freezing


Multiple Choice

5. Which of the following best describes theparticles of a liquid?a. The particles are far apart and moving

fast.b. The particles are close together but

moving past each other.c. The particles are far apart and moving

slowly.d. The particles are closely packed and

vibrate in place.

6. Boiling points and freezing points areexamples ofa. chemical properties. c. energy.b. physical properties. d. matter.

7. During which change of state do atoms ormolecules become more ordered?a. boiling c. meltingb. condensation d. sublimation

8. Which of the following describes whathappens as the temperature of a gas in aballoon increases?a. The speed of the particles

decreases.b. The volume of the gas

increases and the speed of the particles increases.

c. The volume decreases.d. The pressure decreases.

9. Dew collects on a spider web in the earlymorning. This is an example ofa. condensation. c. sublimation.b. evaporation. d. melting.

10. Which of the following changes of state isexothermic?a. evaporation c. freezingb. sublimation d. melting

11. What happens to the volume of a gasinside a piston if the temperature doesnot change but the pressure is reduced?a. increasesb. stays the samec. decreasesd. not enough information

12. The atoms and molecules in mattera. are attracted to one another.b. are constantly moving.c. move faster at higher temperatures.d. All of the above

13. Which of the following contains plasma?a. dry ice c. a fireb. steam d. a hot iron

Short Answer

14. Explain why liquid water takes the shapeof its container but an ice cube does not.

15. Rank solids, liquids, and gases in order ofdecreasing particle speed.

16. Compare the density of iron in the solid,liquid, and gaseous states.

Chapter 376Copyright © by Holt, Rinehart and Winston. All rights reserved.

Concept Mapping

17. Use the followingterms to create a con-cept map: states ofmatter, solid, liquid,gas, plasma, changesof state, freezing,vaporization, conden-sation, melting.


18. After taking a shower, you notice thatsmall droplets of water cover the mirror.Explain how this happens. Be sure todescribe where the water comes from andthe changes it goes through.

19. In the photo below, water is being split toform two new substances, hydrogen andoxygen. Is this a change of state? Explainyour answer.

20. To protect their crops during freezing tem-peratures, orange growers spray wateronto the trees and allow it to freeze. Interms of energy lost and energy gained,explain why this practice protects theoranges from damage.

21. At sea level, water boils at 100°C, whilemethane boils at –161°C. Which of thesesubstances has a stronger force of attrac-tion between its particles? Explain yourreasoning.

MATH IN SCIENCE

22. Kate placed 100 mL of water in fivedifferent pans, placed the pans on awindowsill for a week, and measured howmuch water evaporated. Draw a graph ofher data, shown below, with surface areaon the x-axis. Is the graph linear ornonlinear? What does this tell you?

23. Examine the graph below, and answer thefollowing questions:a. What is the boiling point of the sub-

stance? What is the melting point?b. Which state is present at 30°C?c. How will the substance change if

energy is added to the liquid at 20°C?

80

Tem

pera

ture

(ºC

)

0

20

40

60

Energy !

Take a minute to review your answersto the ScienceLog questions on page59. Have your answers changed? If nec-essary, revise your answers based onwhat you have learned since you beganthis chapter.

States of Matter 77

Pan number 1 2 3 4 5

Surface 44 82 20 30 65area (cm2)

Volume 42 79 19 29 62evaporated (mL)


78

Guiding Lightning

By the time you finish reading this sen-tence, lightning will have flashed morethan 500 times around the world. This

common phenomenon can have devastatingresults. Each year in the United States alone,lightning kills several hundred people and costspower companies more than $100 million.While controlling this awesome outburst ofMother Nature may seem an impossible task,scientists around the world are searching forways to reduce destruction caused by lightning.

Behind the BoltsScientists have learned that during a normallightning strike several events occur. First elec-tric charges build up at the bottom of a cloud.The cloud then emits a line of negativelycharged air particles that zigzags toward theEarth. The attraction between these negativelycharged air particles and positively charged par-ticles from objects on the ground forms aplasma channel. This channel is the pathwayfor a lightning bolt. As soon as the plasmachannel is complete, BLAM!—between 3 and 20lightning bolts separated by thousandths of asecond travel along it.

A Stroke of GeniusArmed with this information, scientists havebegun thinking of ways to redirect these

naturally occurring plasma channels. One ideais to use laser beams. In theory, a laser beamdirected into a thundercloud can charge the airparticles in its path, causing a plasma channelto develop and forcing lightning to strike.

By creating the plasma channels themselves, scientists can, in a way, catch a bolt of lightningbefore it strikes and direct it to a safe area ofthe ground. So scientists simply use lasers todirect naturally occurring lightning to strikewhere they want it to.

A Bright Future?Laser technology is not without its problems,however. The machines that generate laserbeams are large and expensive, and they canthemselves be struck by misguided lightningbolts. Also, it is not clear whether creatingthese plasma channels will be enough to pre-vent the devastating effects of lightning.

Find Out for Yourself! Use the Internet or an electronic database tofind out how rockets have been used in light-ning research. Share your findings with the class.

" Sometime in the future, a laser like thismight be used to guide lightning awayfrom sensitive areas.


79

Full Steam Ahead!

I t was huge. It was 40 m long, about 5 mhigh, and it weighed 245 metric tons. Itcould pull a 3.28 million kilogram train at

100 km/h. It was a 4-8-8-4 locomotive, called aBig Boy, delivered in 1941 to the Union PacificRailroad in Omaha, Nebraska. It was also oneof the final steps in a 2,000-year search to har-ness steam power.

A Simple ObservationFor thousands of years, people used wind,water, gravity, dogs, horses, and cattle toreplace manual labor. But until about 300 yearsago, they had limited success. Then in 1690,Denis Papin, a French mathematician and physi-cist, observed that steam expanding in a cylin-der pushed a piston up. As the steam thencooled and contracted, the piston fell. Watchingthe motion of the piston, Papin had an idea:attach a water-pump handle to the piston. Asthe pump handle rose and fell with the piston,water was pumped.

More Uplifting IdeasEight years later, an English naval captainnamed Thomas Savery made Papin’s devicemore efficient by using water to cool andcondense the steam. Savery’s improved pumpwas used in British coal mines. As good as

Savery’s pump was, the development of steampower didn’t stop there!

In 1712, an English blacksmith namedThomas Newcomen improved Savery’s device byadding a second piston and a horizontal beamthat acted like a seesaw. One end of the beamwas attached to the piston in the steam cylin-der. The other end of the beam was attached tothe pump piston. As the steam piston moved upand down, it created a vacuum in the pumpcylinder and sucked water up from the mine.Newcomen’s engine was the most widely usedsteam engine for more than 50 years.

Watt a Great Idea!In 1764, James Watt, a Scottish technician, wasrepairing a Newcomen engine. He realized thatheating the cylinder, letting it cool, then heatingit again wasted an enormous amount of energy.Watt added a separate chamber where thesteam could cool and condense. The two cham-bers were connected by a valve that let thesteam escape from the boiler. This improvedthe engine’s efficiency—the boiler could stay hotall the time!

A few years later, Watt turned the wholeapparatus on its side so that the piston wasmoving horizontally. He added a slide valve thatadmitted steam first to one end of the chamber(pushing the piston in one direction) and thento the other end (pushing the piston back). Thischanged the steam pump into a true steamengine that could drive a locomotive the size ofBig Boy!

Explore Other Inventions! Watt’s engine helped trigger the IndustrialRevolution as many new uses for steam powerwere found. Find out more about the manyother inventors, from tinkerers to engineers,who harnessed the power of steam.


This Really Happened!In the early morning hours of April 15, 1912,the Titanic, the largest ship ever to set sail,sank on its first voyage. The Titanic wasconsidered to be unsinkable, yet more than1,500 of its passengers and crew werekilled after it hit an iceberg and sank.

How could an iceberg, which ismade of ice, destroy the 2.5 cm thicksteel plates that made up the

Titanic’s hull? Analysis of a recovered pieceof the Titanic’s hull showed that the steelcontained large amounts of the element sul-fur, which is a normal component of steel.However, in this case, the steel containedmuch more sulfur than is the standard forsteel made today. This excessive amount ofsulfur may have caused the steel to be brit-tle, much like glass. Scientists suspect thatthis brittle steel may have cracked on impactwith the iceberg, allowing water to enter thehull.

Could something as simple as using lesssulfur in the Titanic’s steel have preventedthe ship from sinking? It is impossible toknow for sure. What is known, however, isthat the composition and properties of el-ements, compounds, and mixtures are veryimportant in preventing future disasters. Inthis chapter, you will learn about elementsand how they are assembled into com-pounds and mixtures with some very dif-ferent properties.

CH

AP

TE

R

4 Elements,Compounds, and Mixtures

80

This piece of steel hull from theTitanic (at left) was recoveredfrom the wreck.


8. Do you think the process used to create theink involved a physical or chemical change?Explain.

Going FurtherThe procedure you used to separate the componentsof ink is a scientific technique called chromatogra-phy. Find out more about chromatography and itsuses by looking in a chemistry or reference book.

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

1. What is an element?

2. What is a compound? How are compounds and mixtures different?

3. What are the components of a solution called?

Mystery MixtureSteel is just one of the many mixtures that youencounter every day. In fact, you might be usinga mixture to write notes for this activity! Some inksused in pens and markers are a mixture of sev-eral dyes. In this lab, you will separate the partsof an ink mixture.

Procedure1. Cut a 3 ! 15 cm strip of paper from a coffee

filter. Wrap one end around a pencil so thatthe other end will just touch the bottom of aclear plastic cup (as shown in the photoabove). Secure the strip of paper to the pen-cil with a piece of tape.

2. Take the paper out of the cup. Using a water-soluble black marker, make a small dot in thecenter of the strip about 2 cm from the bot-tom end of the paper.

3. Pour water in the cup to a depth of 1 cm.

4. Carefully lower the paper into the cup so thatthe end is in the water but the dot you madeis not underwater.

5. Watch the filter paper. Remove the paper whenthe water is 1 cm from the top of the paper.Record your observations in your ScienceLog.

Analysis6. What happened as the filter paper soaked up

the water? What colors were mixed to makeblack ink?

7. Compare your results with those of your class-mates. How did the mixture in your markercompare with the mixtures in their markers?

81Elements, Compounds, and MixturesCopyright © by Holt, Rinehart and Winston. All rights reserved.

Chapter 482

N E W T E R M Selement nonmetalspure substance metalloidsmetals

O B J E CT I V E S! Describe pure substances.! Describe the characteristics of

elements, and give examples.! Explain how elements can be

identified.! Classify elements according to

their properties.

Section1 Elements

Imagine you are working as a lab technician for the Break-It-Down Corporation. Your job is to break down incomingmaterials into the simplest substances you can obtain. Oneday a material seems particularly difficult to break down. Youstart by crushing and grinding it. You notice that the result-ing pieces are smaller, but they are still the same material.You try other physical changes, including melting, boiling,and filtering it, but the material does not change into any-thing simpler.

Next you try some chemical changes. For example, youpass electric current through the material. Although manysubstances can be broken down using electric current, thismaterial still does not become any simpler. After recordingyour observations, you analyze the results of your tests. Youthen draw a conclusion: the substance must be an element.An element is a pure substance that cannot be separated intosimpler substances by physical or chemical means, as shownin Figure 1.

An Element Has Only One Type of ParticleA pure substance is a substance in which there is only onetype of particle. Because elements are pure substances, eachelement contains only one type of particle. For example, everyparticle (atom) in a 5 g nugget of the element gold is likeevery other particle of gold. The particles of a pure substanceare alike no matter where that substance is found. Take a lookat Figure 2. The element iron is a major component of manymeteorites. Although a meteorite might travel more than 400 million kilometers (about 248 million miles) to reach Earth,the particles of iron in a meteorite are identical to the parti-cles of iron in objects around your home!

Figure 1 No matter what kind ofphysical or chemical change youattempt, an element cannot bechanged into a simpler substance!

Figure 2 The atoms of theelement iron are alike whetherthey are in a meteorite or in acommon iron skillet.


Every Element Has a Unique Set of PropertiesEach element has a unique set of properties that allows youto identify it. For example, each element has its own charac-teristic properties. These properties do not depend on the amountof material present in a sample of the element. Characteristicproperties include some physical properties, such as boilingpoint, melting point, and density, as well as chemical prop-erties, such as reactivity with acid. The elements helium andkrypton are unreactive gases. However, the density (mass perunit volume) of helium is less than the density of air. Therefore,a helium-filled balloon will float up if it is released. Kryptonis more dense than air, so a krypton-filled balloon will sink tothe ground if it is released.

Look at the elements cobalt,iron, and nickel, shown in Figure 3.Even though these three elementshave some similar properties, eachcan be identified by its unique setof properties.

Notice that the physical prop-erties for the three elementsinclude melting point and den-sity. Other physical properties,such as color, hardness, and tex-ture, could be added to the list.Also, depending on the elementsbeing identified, other chemicalproperties might be useful. Forexample, some elements, such ashydrogen and carbon, are flam-mable. Other elements, such assodium, react immediately withoxygen. Still other elements, suchas zinc, are reactive with acid.

Most Elements Are Combined in Nature Most elementsare found combined with other elements in nature. The rea-son lies in their chemical properties. Most elements undergochemical changes when combined with oxygen or water. Whenthese elements are exposed to air or moisture, they undergochemical changes and form more-complex substances calledcompounds. (You’ll learn more about compounds in the nextsection.) Some elements do not react readily with water or airand can be found uncombined in nature. These elementsinclude gold, copper, sulfur, neon, and carbon.

Elements, Compounds, and Mixtures 83

Figure 3 Like all other elements, cobalt, iron, and nickel can beidentified by their unique combination of properties.

Melting point is 1,495°C.Density is 8.9 g/cm3.Conducts electricity and heat.Unreactive with oxygen in the air.

Cobalt

Melting point is 1,535°C.Density is 7.9 g/cm3.Conducts electricity and heat.Combines slowly with oxygenin the air to form rust.

Iron

Melting point is 1,455°C.Density is 8.9 g/cm3.Conducts electricity and heat.Unreactive with oxygen in the air.

Nickel


Elements Are Classified by Their PropertiesConsider how many different breeds of dogs there are. Consideralso how you tell one breed from another. Most often you cantell just by their appearance, or what might be called physi-

cal properties. Figure 4 shows several breeds of dogs,which all happen to be terriers. Many terriers are

fairly small in size and have short hair. Many alsoshare the same basic body shape. Even the behav-ior of chasing small animals like rats or foxes isshared by most terriers. Although terriers arenot exactly alike, they share enough commonproperties to be classified in the same group.

Similarly, elements are classified into groupsaccording to their shared properties. Recall the

elements iron, nickel, and cobalt. All three areshiny, and all three conduct thermal energy and

electric current. Using these shared properties, sci-entists have grouped these three elements, along with other

elements that are shiny and are good conductors, into onelarge group called metals. Metals are not all exactly alike, butthey do have some properties in common. Likewise, you cangroup elements that are not shiny and are not good conduc-tors into a different group called nonmetals.

If You Know the Category, You Know the Properties Ifyou have ever browsed at a music store, you know that the CDsand tapes are categorized by basic type of music. If you are inter-ested in rock-and-roll, you would go to the rock-and-roll sec-tion. Even though you might not recognize a particular CD, you know that it must have the characteristics of rock-and-roll for it to be in this section. Otherwise, it would be kept in

the classical, bluegrass, country, or some other section.Likewise, you can predict some of the properties

of an unfamiliar element by knowing the categoryto which it belongs. As shown in the concept

map in Figure 5, elements are classified intothree categories—metals, nonmetals, and

metalloids. Cobalt, iron, and nickel are clas-sified as metals. If you know that a par-ticular element is a metal, you know thatit shares certain properties with iron,nickel, and cobalt. The chart on the nextpage shows examples of elements ineach category and a summary of theproperties that identify the members ofeach category.

Figure 4 Even though thesedogs are different breeds, theyhave enough in common to beclassified as terriers.

Metals Nonmetals Metalloids

are divided into

Elements

Chapter 484

Figure 5 Elements are divided into three categories:metals, nonmetals, and metalloids.



MetalloidsMetalloids, also called semiconductors, are elementsthat have properties of both metals and nonmetals.Some metalloids are shiny, while others are dull.Metalloids are somewhat malleable and ductile. Somemetalloids conduct thermal energy and electric currentwell. Other metalloids can become good conductorswhen they are mixed with other elements. Silicon isused to make computer chips. However, other elementsmust be mixed with silicon to make a working chip.

MetalsMetals are elements that are shiny and aregood conductors of thermal energy and elec-tric current. They are easily shaped into dif-ferent forms because they are malleable (theycan be hammered into thin sheets) andductile (they can be drawn into thin wires).Iron has many uses in building and auto-mobile construction. Copper is used in wiresand coins.

The Three Major Categories of Elements

1. What is a pure substance?

2. List three properties that can be used to classify elements.

3. Applying Concepts Which category of element would be the least appropriate choice for making a containerthat can be dropped without shattering? Explain yourreasoning.

REVIEW

Sulfur

NonmetalsNonmetals are elements that are dull (not shiny) andthat are poor conductors of thermal energy and elec-tric current. Solid nonmetals tend to be brittle andunmalleable. Few familiar objects are made of onlynonmetals. The neon used in lights is a nonmetal, asis the graphite (carbon) used in pencils.

Neon

TinCopper

Silicon

Antimony

Lead

Bromine

Boron


Chapter 486

N E W T E R M Scompound

O B J E CT I V E S! Describe the properties of

compounds.! Identify the differences between

an element and a compound.! Give examples of common

compounds.

Section2 Compounds

You learned in Section 1 that because most elements take partin chemical changes fairly easily, few elements are found alonein nature. Instead, most elements are found combined withother elements as compounds.

A compound is a pure substance composed of two or moreelements that are chemically combined. In a compound, a par-ticle is formed when particles of two or more elements join toform a single larger particle. In order for elements to combine,they must react, or undergo a chemical change, with oneanother. In Figure 6, you see magnesium reacting with oxygento form a compound called magnesium oxide. The compoundis a new pure substance that is different from the elements thatreacted to form it.

Most substances you en-counter every day are com-pounds. For example, tablesalt is a compound composedof the elements sodium andchlorine chemically combined.Water is a compound com-posed of the elements hydro-gen and oxygen chemicallycombined. Calcium phos-phate, an important com-pound in bones and teeth, iscomposed of the elements cal-cium, phosphorus, and oxy-gen chemically combined.

Elements Combine in a Definite Ratio to Form a CompoundCompounds are not random combinations of elements. Whena compound forms, the elements join in a specific ratio accord-ing to their masses. For example, the ratio of the mass of hydro-gen to the mass of oxygen in water is always the same—1 gof hydrogen to 8 g of oxygen. This mass ratio can be writtenas 1:8 or as the fraction 1/8. Every sample of water has this1:8 mass ratio of hydrogen to oxygen. If a sample of a com-pound has a different mass ratio of hydrogen to oxygen, thecompound cannot be water. The mass ratio of hydrogen tooxygen in the compound hydrogen peroxide is 1:16. The massratio of carbon to oxygen in carbon monoxide is 3:4, but incarbon dioxide the mass ratio is 3:8.

Figure 6 As magnesium burns, it reacts with oxygen and formsthe compound magnesium oxide.Magnesium is used often in themanufacture of fireworksbecause of the bright white lightproduced during this chemicalchange.


Every Compound Has a Unique Set of PropertiesEach compound has a unique set of properties that allows youto distinguish it from other compounds. Like elements, eachcompound has its own physical properties, such as boilingpoint, melting point, density, and color. Compounds can alsobe identified by their different chemical properties. Some com-pounds, such as calcium carbonate found in chalk, react withacid. Others, such as hydrogen peroxide, react when exposedto light. You can see how chemical properties can be used toidentify compounds in the QuickLab at right.

A compound has different properties from the elementsthat form it. Did you know that ordinary table salt is a com-pound made from two very dangerous elements? Table salt—sodium chloride—consists of sodium (which reacts violentlywith water) and chlorine (which is poisonous). Together, how-ever, these elements form a harmless compound with uniqueproperties. Take a look at Figure 7. Because a compound hasdifferent properties from the elements that react to form it,sodium chloride is safe to eat and dissolves (without explod-ing!) in water.

Another example to consider can be found in Figure 6 onthe previous page. The element oxygen is a colorless gas, andthe element magnesium is a silvery white metal. However, thecompound magnesium oxide is a white powdery solid.


Compound Confusion1. Measure 4 g (1 tsp)

of compound A,and place it in aclear plastic cup.

2. Measure 4 g (1 tsp)of compound B,and place it in asecond clear plastic cup.

3. Observe the color andtexture of each compound.Record your observations.

4. Add 5 mL (1 tsp) ofvinegar to each cup.Record your observations.

5. Baking soda reacts withvinegar, while powderedsugar does not. Which ofthese compounds iscompound A, and which iscompound B?

Self-CheckDo the properties of pure water from a glacier andfrom a desert oasis differ? (See page 596 to checkyour answer.)

Figure 7 Table salt is formed when theelements sodium and chlorine join. Theproperties of salt are different from theproperties of sodium and chlorine.

Chlorine is a poisonous,greenish yellow gas.

Sodium is a soft, silverywhite metal that reactsviolently with water.

Sodium chloride, or table salt, isa white solid that dissolves easilyin water and is safe to eat.


Compounds Can Be Broken Down intoSimpler SubstancesIf some elements are found only in compounds, how can puresamples of these elements be produced? Compounds can bebroken down into elements through chemical changes. Lookat Figure 8. When the compound mercury(II) oxide is heated,it breaks down into the elements mercury and oxygen. Likewise,if electricity is passed through melted table salt, the elementssodium and chlorine are produced.

Some compounds undergo chemical changes to form sim-pler compounds. These compounds can be broken down intoelements through additional chemical changes. For example,carbonic acid is a compound that helps to give carbonatedbeverages their “fizz.” Carbonic acid breaks down to form thecompounds water and carbon dioxide gas. You can cause thischemical change by simply opening a bottle of a carbonated

drink to release the pressure, asshown in Figure 9. The carbon

dioxide and water that areformed can be further brokendown into the elements car-bon, oxygen, and hydrogenthrough additional chemi-cal changes.

Compounds Cannot Be Broken Down by Physical ChangesThe only way to break down a compound is through a chemi-cal change. If you pour water through a filter, the water willpass through the filter unchanged. Filtration is a physicalchange, so it cannot be used to break down a compound.Likewise, a compound cannot be broken down by grinding itinto a powder or by any other physical process.

One chemical process that can be used to break down com-pounds is electrolysis. In electrolysis, electric current is usedto break down compounds. Electrolysis can be used to sepa-rate water into hydrogen and oxygen.

Chapter 488

Figure 8 Heating mercury(II)oxide causes a chemical changethat separates it into the el-ements mercury and oxygen.

Oxygen

Mercury

Mercury(II) oxide

physicsC O N N E C T I O N

The process of using electriccurrent to break compoundsinto simpler compounds andelements is known as elec-trolysis. The amount of com-pounds and elementsproduced depends on theamount of the original com-pound present, the amount ofcurrent, and the length of timethe electric current flows. Theelements aluminum and cop-per and the compound hydro-gen peroxide are importantindustrial products obtainedthrough electrolysis.

Figure 9 Opening a carbon-ated drink can be messy ascarbonic acid breaks downinto two simpler compounds—carbon dioxide and water.


Help keep the fireworks colorfulon page 530 of the LabBook.

Compounds in Your WorldYou are always surrounded by compounds. Compounds makeup the food you eat, the school supplies you use, the clothesyou wear—even you! Compounds are formed and broken downevery day in nature and in industry.

Compounds in Nature Proteins are compounds found inall living things. The element nitrogen is needed to make pro-teins. Although nitrogen makes up 78 percent of the atmos-phere, plants and animals cannot use nitrogen directly fromthe air. Some plants overcome this problem as shown inFigure 10. Other plants use nitrogen compounds that are inthe soil. Animals get the nitrogen they need by eating plantsor by eating animals that have eaten plants. As an animaldigests food, the proteins in the food are broken down intosmaller compounds that the animal’s cells can use. That’s whyyou need to eat your fruits and vegetables!

Another compound that plays an important role in life iscarbon dioxide. You exhale carbon dioxide that was made inyour body. Plants take in carbon dioxide and use it to makeother compounds, including sugar.

Compounds in Industry To help plants get enough nitro-gen, a nitrogen compound called ammonia is manufacturedfor use in fertilizers. The element nitrogen is combined withthe element hydrogen to form ammonia. Plants can use ammo-nia as a source of nitrogen for their proteins. Other manufac-tured compounds are used in medicines, food preservatives,and synthetic fabrics.

The compounds found in nature are usually not the rawmaterials needed by industry. Often, these compounds mustbe broken down to form elements needed as raw material. Forexample, the element aluminum is used in cans, airplanes, andbuilding materials, but it is not found alone in nature.Aluminum is produced by breaking down the compound alu-minum oxide.


Figure 10 The bumps on theroots of this pea plant are hometo bacteria that form compoundsfrom atmospheric nitrogen. Thepea plant makes proteins fromthese compounds.

1. What is a compound?

2. What type of change is needed to break down a compound?

3. Analyzing Ideas A jar contains samples of the elementscarbon and oxygen. Does the jar contain a compound?Explain.

REVIEW


Chapter 490

N E W T E R M Smixture concentrationsolution solubilitysolute suspensionsolvent colloidalloys

O B J E CT I V E S! Describe the properties of

mixtures.! Describe methods of separating

the components of a mixture.! Analyze a solution in terms

of its solute, solvent, and concentration.

! Compare the properties of solu-tions, suspensions, and colloids.

Section3 Mixtures

Have you ever madeyour own pizza? Youroll out the dough, adda layer of tomato sauce,then add toppings likegreen peppers, mushrooms,and olives—maybe even somepepperoni! Sprinkle cheese ontop, and you’re ready to bake. Youhave just created not only a pizza but also amixture—and a delicious one at that!

Properties of MixturesAll mixtures—even pizza—share certain properties. A mixtureis a combination of two or more substances that are not chemi-cally combined. Two or more materials together form a mix-ture if they do not react to form a compound. For example,cheese and tomato sauce do not react when they are used tomake a pizza.

Substances in a Mixture Retain Their Identity Becauseno chemical change occurs, each substance in a mixture hasthe same chemical makeup it had before the mixture formed.That is, each substance in a mixture keeps its identity. Insome mixtures, such as the pizza above or the piece of gran-ite shown in Figure 11, you can even see the individual com-ponents. In other mixtures, such as salt water, you cannotsee all the components.

Mixtures Can Be Physically Separated If you don’t likemushrooms on your pizza, you can simply pick them off withyour fingers. This separation is a physical change of the mix-ture, because the identities of the substances are not changedin the process. In contrast, compounds can be broken downonly through chemical changes.

Each substance in a mixture retains most of its character-istic properties, such as density and boiling point. In fact, theseproperties can often be used to separate the components of amixture. You cannot simply pick salt out of a saltwater mix-ture, but you can separate the salt from the water by heatingthe mixture. The water undergoes a physical change by vapor-izing, or changing state from a liquid to a gas. The salt remainsbehind as a white solid. Several common techniques for sepa-rating mixtures are shown on the following page.

Figure 11 Colorless quartz, pinkfeldspar, and black mica makeup the mixture granite. You canidentify each component becausethe identity of a substance doesnot change in a mixture.



Common Techniques for Separating Mixtures

1 2 3

Distillation is a process that separates a mixturebased on the boiling points of the components.Here you see pure water being distilled from asaltwater mixture. In addition to water purifica-tion, distillation is used to separate crude oil intoits components, including gasoline and kerosene.

A magnet can be used to separate a mixture of the

elements iron and aluminum. Iron isattracted to the

magnet, but aluminum is not.

The components that make up blood are separated using a machine called a centrifuge. This machine separates mixtures according to the densities of the components.

A mixture of the compoundsodium chloride (table salt)with the element sulfur requiresmore than one separation step.

The first step is to mix themwith another compound—water.Salt dissolves in water, but sul-fur does not.

In the second step, the mixtureis poured through a filter. Thefilter traps the solid sulfur.

In the third step, the sodiumchloride is separated from thewater by simply evaporating thewater.


The Components of a Mixture Do Not Have a DefiniteRatio Recall that a compound has a specific mass ratio of theelements that form it. Unlike compounds, the components ofa mixture do not need to be combined in a definite ratio. Forexample, granite that has a greater amount of feldspar thanmica or quartz appears to have a pink color. Granite that hasa greater amount of mica than feldspar or quartz appears black. Regardless of which ratio is present, this combination ofmaterials is always a mixture—and it is always called granite.

Air is a mixture composed mostly of nitrogen and oxygen,with smaller amounts of other gases, such as carbon dioxideand water vapor. Some days the air has more water vapor, oris more humid, than on other days. But regardless of the ratioof the components, air is still a mixture.

The chart at left summarizes the differences between mix-tures and compounds.

SolutionsA solution is a mixture that appears to be a single substancebut is composed of particles of two or more substances thatare distributed evenly amongst each other. Solutions are oftendescribed as homogeneous mixtures because they have the sameappearance and properties throughout the mixture.

The process in which particles of substances separate andspread evenly throughout a mixture is known as dissolving. Insolutions, the solute is the substance that is dissolved, and thesolvent is the substance in which the solute is dissolved. Asolute is soluble, or able to dissolve, in the solvent. A substancethat is insoluble, or unable to dissolve, forms a mixture that isnot homogeneous and therefore is not a solution.

Salt water is a solution. Salt is soluble in water, meaningthat salt dissolves in water. Therefore, salt is the solute andwater is the solvent. When two liquids or two gases form asolution, the substance with the greater volume is the solvent.

Chapter 492

Mixtures vs. Compounds

Mixtures

Componentsare elements,compounds, or both

Componentskeep theiroriginal properties

Separated by physicalmeans

Formed usingany ratio ofcomponents

Compounds

Componentsare elements

Componentslose their origi-nal properties

Separated by chemicalmeans

Formed usinga set massratio of components

Many substances are solu-ble in water, including salt,sugar, alcohol, and oxygen.Water does not dissolveeverything, but it dissolvesso many different solutesthat it is often called theuniversal solvent.

REVIEW

1. What is a mixture?

2. Is a mixture separated by physical or chemical changes?

3. Applying Concepts Suggest a procedure to separate ironfilings from sawdust. Explain why this procedure works.


You may think of solutions as being liquids. And, in fact,tap water, soft drinks, gasoline, and many cleaning suppliesare liquid solutions. However, solutions may also be gases,such as air, and solids, such as steel. Alloys are solid solutionsof metals or nonmetals dissolved in metals. Brass is an alloyof the metal zinc dissolved in copper. Steel, including thatused to build the Titanic, is an alloy made of the nonmetalcarbon and other elements dissolved in iron. Look at the chartbelow for examples of the different states of matter used assolutes and solvents in solutions.

Particles in Solutions Are Extremely Small The particlesin solutions are so small that they never settle out, nor canthey be filtered out of these mixtures. In fact, the particles areso small, they don’t even scatter light. Look at Figure 12 andsee for yourself. The jar on the left contains a solution ofsodium chloride in water. The jar on the right contains a mix-ture of gelatin in water.

93

Figure 12 Both of these jarscontain mixtures. The mixture inthe jar on the left, however, is asolution. The particles in solu-tions are so small they don’tscatter light. Therefore, you can’tsee the path of light through it.

Self-CheckYellow gold is an alloymade from equal partscopper and silver com-bined with a greateramount of gold.Identify each compo-nent of yellow gold asa solute or solvent.(See page 596 to checkyour answer.)

Gas in gas Dry air (oxygen in nitrogen)

Gas in liquid Soft drinks (carbon dioxide in water)

Liquid in liquid Antifreeze (alcohol in water)

Solid in liquid Salt water (salt in water)

Solid in solid Brass (zinc in copper)

Examples of Different States in Solutions


Concentration: How Much Solute Is Dissolved? A meas-ure of the amount of solute dissolved in a solvent is concentration. Concentration can be expressed in grams ofsolute per milliliter of solvent. Knowing the exact concentra-tion of a solution is very important in chemistry and medi-cine because using the wrong concentration can be dangerous.

Solutions can be described as being concentrated or dilute.Look at Figure 13. Both solutions have the same amount ofsolvent, but the solution on the left contains less solute thanthe solution on the right. The solution on the left is dilutewhile the solution on the right is concentrated. Keep in mindthat the terms concentrated and dilute do not specify the amountof solute that is actually dissolved. Try your hand at calculat-ing concentration and describing solutions as concentrated ordilute in the MathBreak at left.

A solution that contains all the solute it can hold at a giventemperature is said to be saturated. An unsaturated solution con-tains less solute than it can hold at a given temperature. Moresolute can dissolve in an unsaturated solution.

Solubility: How Much Solute Can Dissolve? If you addtoo much sugar to a glass of lemonade, not all of the sugarcan dissolve. Some of the sugar collects on the bottom of theglass. To determine the maximum amount of sugar that candissolve, you would need to know the solubility of sugar. Thesolubility of a solute is the amount of solute needed to makea saturated solution using a given amount of solvent at a cer-tain temperature. Solubility is usually expressed in grams ofsolute per 100 mL of solvent. Figure 14 on the next page showsthe solubility of several different substances in water at dif-ferent temperatures.

Chapter 494

Figure 13 The dilute solution on the left contains less solute thanthe concentrated solution on the right.

Calculating ConcentrationMany solutions are colorless.Therefore, you cannot alwayscompare the concentrations ofsolutions by looking at thecolor—you have to comparethe actual calculated concen-trations. One way to calculatethe concentration of a liquidsolution is to divide the gramsof solute by the milliliters ofsolvent. For example, the con-centration of a solution inwhich 35 g of salt is dissolvedin 175 mL of water is

!17535

mgL

swal

atter! ! 0.2 g/mL

Now It’s Your TurnCalculate the concentrationsof each solution below.Solution A has 55 g of sugardissolved in 500 mL of water.Solution B has 36 g of sugardissolved in 144 mL of water.Which solution is moredilute? Which is more concentrated?

MATH BREAK

Smelly solutions? Follow your nose and learn

more on page 102.


Unlike the solubility of most solids in liquids, the solubil-ity of gases in liquids decreases as the temperature is raised.As you heat a pot of water, bubbles of gas appear in the waterlong before the water begins to boil. The gases that are dis-solved in the water cannot remain dissolved as the tempera-ture increases because the solubility of the gases is lower athigher temperatures.

What Affects How Quickly Solids Dissolve in Liquids?Many of the solutions used in your science class and in yourhome are formed when a solid solute is dissolved in water.Several factors affect how fast the solid will dissolve. Lookat Figure 15 to see three methods used to make a solute dis-solve faster. You can see why you will enjoy a glass of lemon-ade sooner if you stir granulated sugar into the lemonadebefore adding ice!


Figure 15 Mixing, heating, and crushing iron(III) chlorideincrease the speed at which it will dissolve.

200

240

160

120

80

40

0 80 10020 40 60

Temperature (ºC)

Solu

bilit

y (g

/100

mL

of w

ater

)

Sodium chloride

Sodium nitrate

Cerium sulfate

Potassium bromide

Sodium chlorate

Figure 14 Solubility of DifferentSubstances

The solubility of most solids increases as thetemperature gets higher. Thus, more solute can dissolve at higher temperatures. However,some solids, such as cerium sulfate, are lesssoluble at higher temperatures.

Mixing by stirring or shakingcauses the solute particles to separate from one another andspread out more quickly amongthe solvent particles.

Heating causes particles tomove more quickly. The solventparticles can separate the soluteparticles and spread them outmore quickly.

Crushing the solute increasesthe amount of contact betweenthe solute and the solvent. Theparticles of solute mix with thesolvent more quickly.


SuspensionsWhen you shake up a snow globe, you aremixing the solid snow particles with theclear liquid. When you stop shaking theglobe, the snow particles settle to the bot-tom of the globe. This mixture is called asuspension. A suspension is a mixture inwhich particles of a material are dispersedthroughout a liquid or gas but are largeenough that they settle out. The particlesare insoluble, so they do not dissolve inthe liquid or gas. Suspensions are oftendescribed as heterogeneous mixtures becausethe different components are easily seen.Other examples of suspensions include muddy waterand Italian salad dressing.

The particles in a suspension are fairlylarge, and they scatter or block light. Thisoften makes a suspension difficult to seethrough. But the particles are too heavy toremain mixed without being stirred orshaken. If a suspension is allowed to situndisturbed, the particles will settle out,as in a snow globe.

A suspension can be separated by pass-ing it through a filter. The liquid or gaspasses through, but the solid particles arelarge enough to be trapped by the filter, asshown in Figure 16.

Figure 16 Dirty air is a suspension that could damagea car’s engine. The air filter ina car separates dust from airto keep the dust from gettinginto the engine.

M any medicines, such asremedies for upset stom-

ach, are suspensions. The direc-tions on the label instruct you toshake the bottle well before use.Why must you shake the bottle?What problem could arise if youdon’t?

Chapter 496

life scienceC O N N E C T I O N

Blood is a suspension. Thesuspended particles, mainlyred blood cells, white bloodcells, and platelets, are actuallysuspended in a solution calledplasma. Plasma is 90 percentwater and 10 percent dis-solved solutes, including sugar,vitamins, and proteins.


ColloidsSome mixtures have properties of both solu-tions and suspensions. These mixtures areknown as colloids (KAWL OYDZ). A colloidis a mixture in which the particles are dis-persed throughout but are not heavy enoughto settle out. The particles in a colloid arerelatively small and are fairly well mixed. Solids,liquids, and gases can be used to make colloids.You might be surprised at the number of colloidsyou encounter each day. Milk, mayonnaise, stickdeodorant—even the gelatin and whipped creamin Figure 17—are colloids. The materials that com-pose these products do not separate between usesbecause their particles do not settle out.

Although the particles in a colloid are much smaller thanthe particles in a suspension, they are still large enough to scat-ter a beam of light shined through the colloid, as shown inFigure 18. Finally, unlike a suspension, a colloid cannot be sepa-rated by filtration. The particles are small enough to passthrough a filter.


Figure 18 The colloid fog cancreate a dangerous situation fordrivers. The particles in fog scat-ter light, making it difficult fordrivers to see the road ahead.

Figure 17 This dessert

includes two delicious examples

of colloids—fruity gelatin and

whipped cream.

1. List two methods of making a solute dissolve faster.

2. Identify the solute and solvent in a solution made from15 g of oxygen and 5 g of helium.

3. Comparing Concepts What are three differences betweensolutions and suspensions?

REVIEW

Make a colloid found in yourkitchen on page 533 of the

LabBook.


Chapter Highlights

Chapter 498

SECTION 1 SECTION 2

Skills Check

SECTION 2

Vocabularyelement (p. 82)pure substance (p. 82)metals (p. 85)nonmetals (p. 85)metalloids (p. 85)

Section Notes• A substance in which all the

particles are alike is a puresubstance.

• An element is a pure sub-stance that cannot be bro-ken down into anythingsimpler by physical orchemical means.

• Each element has a uniqueset of physical and chemicalproperties.

• Elements are classified asmetals, nonmetals, andmetalloids based on theirproperties.

Vocabularycompound (p. 86)

Section Notes• A compound is a pure sub-

stance composed of two ormore elements chemicallycombined.

• Each compound has aunique set of physical andchemical properties that aredifferent from the propertiesof the elements that com-pose it.

• The elements that form acompound always combinein a specific ratio accordingto their masses.

• Compounds can be brokendown into simpler sub-stances by chemicalchanges.

LabsFlame Tests (p. 530)

Visual UnderstandingTHREE CATEGORIES OF ELEMENTSElements are classified into metals,nonmetals, and metalloids, basedon their properties. The chart on page85 provides a summary of the properties that distinguish each category.

SEPARATING MIXTURES Mixtures can beseparated through physical changes based ondifferences in the physical properties of theircomponents. Review the illustrations on page91 for some techniques for separating mixtures.

Math ConceptsCONCENTRATION The concentration of asolution is a measure of the amount of solutedissolved in a solvent. For example, a solutionis formed by dissolving 85 g of sodium nitratein 170 mL of water. The concentration of thesolution is calculated as follows:

85 g sodium nitrate = 0.5 g/mL170 mL water


99Elements, Compounds, and Mixtures

SECTION 3


TOPIC: The Titanic sciLINKS NUMBER: HSTP080TOPIC: Elements sciLINKS NUMBER: HSTP085TOPIC: Compounds sciLINKS NUMBER: HSTP090TOPIC: Mixtures sciLINKS NUMBER: HSTP095


KEYWORD: HSTMIX


Vocabularymixture (p. 90)solution (p. 92)solute (p. 92)solvent (p. 92)alloys (p. 93)concentration (p. 94)solubility (p. 94)suspension (p. 96)colloid (p. 97)

Section Notes• A mixture is a combination

of two or more substances,each of which keeps its owncharacteristics.

• Mixtures can be separatedby physical means, such asfiltration and evaporation.

• The components of a mix-ture can be mixed in anyproportion.

• A solution is a mixture thatappears to be a single sub-stance but is composed of asolute dissolved in a solvent.Solutions do not settle, can-not be filtered, and do notscatter light.

• Concentration is a measureof the amount of solute dis-solved in a solvent.

• The solubility of a solute is the amount of soluteneeded to make a saturatedsolution using a givenamount of solvent at a certain temperature.

• Suspensions are hetero-geneous mixtures that con-tain particles large enoughto settle out, be filtered, andblock or scatter light.

• Colloids are mixtures thatcontain particles too smallto settle out or be filteredbut large enough to scatterlight.

LabsA Sugar Cube Race! (p. 532)Making Butter (p. 533)Unpolluting Water (p. 534)


Chapter Review

Chapter 4100

Complete the following sentences by choos-ing the appropriate term from the vocabularylist to fill in each blank:

1. A ? has a definite ratio of components.

2. The amount of solute needed to form asaturated solution is the ? of thesolute.

3. A ? can be separated by filtration.

4. A pure substance must be either a(n) ? or a(n) ? .

5. Elements that are brittle and dull are ? .

6. The substance that dissolves to form asolution is the ? .


Multiple Choice

7. Which of the following increases the solu-bility of a gas in a liquid?a. increasing the temperatureb. stirringc. decreasing the temperatured. decreasing the amount of liquid

8. Which of the following best describeschicken noodle soup?a. element c. compoundb. mixture d. solution

9. Which of the following doesnot describe elements?a. all the particles are alikeb. can be broken down into simpler

substancesc. have unique sets of propertiesd. can join together to form compounds

10. A solution that contains a large amountof solute is best described asa. unsaturated. c. dilute.b. concentrated. d. weak.

11. Which of the following substances can beseparated into simpler substances only bychemical means?a. sodium c. waterb. salt water d. gold

12. Which of the following would not in-crease the rate at which a solid dissolves?a. decreasing the temperatureb. crushing the solidc. stirringd. increasing the temperature

13. An element that conducts thermal energywell and is easily shaped is aa. metal.b. metalloid.c. nonmetal.d. None of the above

14. In which classification of matter are thecomponents chemically combined?a. alloy c. compoundb. colloid d. suspension

Short Answer

15. What is the difference between an element and a compound?

16. Identify the solute and solvent if nailpolish is dissolved in acetone.

100

USING VOCABULARY



101Elements, Compounds, and Mixtures

Concept Mapping

17. Use the followingterms to create aconcept map: matter, element,compound, mixture,solution, suspension,colloid.

18. Describe a procedure to separate a mixtureof salt, finely ground pepper, and pebbles.

19. A light green powder isheated in a test tube. Agas is given off, whilethe solid becomes black.In which classificationof matter does the greenpowder belong? Explainyour reasoning.

20. Why is it desirable to know the exact concentration of solutionsrather than whether they are concentratedor dilute?

21. Explain the three properties of mixturesusing a fruit salad as an example.

22. To keep the “fizz” in carbonated beveragesafter they have been opened, should youstore them in a refrigerator or in a cabi-net? Explain.

MATH IN SCIENCE

23. What is the concentration of a solutionprepared by mixing 50 g of salt with 200 mL of water?

24. How many grams of sugar must be dis-solved in 150 mL of water to make a solu-tion with a concentration of 0.6 g/mL?


25. Use Figure 14 on page 95 to answer thefollowing questions:a. Can 50 g of sodium chloride dissolve in

100 mL of water at 60°C?b. How much cerium sulfate is needed to

make a saturated solution in 100 mL ofwater at 30°C?

c. Is sodium chloride or sodium nitratemore soluble in water at 20°C?

26. Dr. Sol Vent tested the solubility of acompound. The data below was collectedusing 100 mL of water. Graph Dr. Vent’sresults. To increase the solubility, wouldyou increase or decrease the temperature?Explain.

27. What type of mixture is shown in thephoto below? Explain.

GO TO: www.scilinks.org

Temperature (°C) 10 25 40 60 95

Dissolved solute (g) 150 70 34 25 15

Take a minute to review your answersto the ScienceLog questions on page81. Have your answers changed? Ifnecessary, revise your answers based onwhat you have learned since you beganthis chapter.

101


MATH IN SCIENCE



CHAPTER 2 The Properties of Matter - Mrs. Erin · PDF file36 Chapter 2 NEW TERMS matter...

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