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How ArePlaying Cards &

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How ArePlaying Cards &

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(bkgd.)Granger Collection, NY, (inset)National Geographic Society

Visit gpscience.com/unit_project to find project ideas and resources.Projects include:• History Discover the diverse uses of lasers. Compile a class spider map of

laser use in different professions.• Technology Research elements and create a 3-dimensional periodic table

with characteristics of each element on element cubes.• Model Design and construct a unit review game to include questions,

answers, directions, playing pieces, and a creative box.Art of Neon is an investigation of the noble gases and how theyare inserted into glass tubes to be used in art and signage.

By 1860, scientists knew of about 60 elements. However, they had yet to clearly organize their knowledge. A Russian scientist named

Dmitri Mendeleev changed that. Mendeleev loved to play solitaire, atype of card game in which playing cards are arranged into patternsaccording to their properties. One day, Mendeleev decided to make aset of cards on which he wrote the names and properties of the knownelements. Then he began to arrange the cards into rows. The resultwas a table in which certain chemical properties could be seen to occurperiodically—that is, to occur in a repeating pattern. In 1869,Mendeleev published his periodic table (seen here in a more advancedversion). He left blank spaces in the table where the pattern seemed tocall for elements that were not yet known. Over the next severaldecades, other scientists refined the table, and new elements wereadded. Modern periodic tables—like the one probably hanging in yourclassroom—still follow the basic pattern laid out by Mendeleev.

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sections

1 Composition of MatterLab Elements, Compounds,and Mixtures

2 Properties of MatterLab Checking Out ChemicalChanges

Virtual Lab How canmolecular models be built?

The Ar t of MixturesWhen painting, colors can be skillfully mixedto achieve a certain shade, or the artist canshow several individual pigments in a singlebrush stroke. Paint undergoes physical andchemical changes with time that can make theartist’s work endure.

Describe the changes that takeplace as the paint dries, particularly which changes arephysical and which ones are chemical.

Science Journal

Classification of Matter

(bkgd.)Michael Newman/PhotoEdit, Inc.

449449

Start-Up Activities

Classification of Matter Makethe following Foldable to

ensure that you have understood the content bydefining the vocabulary terms from this chapter.

Fold a vertical sheetof paper from side toside. Make the frontedge about 1.25 cmshorter than theback edge.

Turn lengthwise,with the fold ontop, and fold intothirds.

Unfold and cut only the top layeralong both folds to make three tabs.

Label the tabs Elements, Compounds,and Mixtures as shown.

Define As you read the chapter, define eachterm and list examples of each under theappropriate tab.

STEP 4

STEP 3

STEP 2

STEP 1

1. Place 75 mL ofwater in a 200-mLbeaker and add 20 drops of redfood coloring.

2. Place the beakeron a hot plate.

3. Add ice to an evaporating dish until thedish is half full. Add boiling chips. Placethe evaporating dish on the beaker asshown in the photo.

4. Turn on the hot plate and slowly bring thewater and food coloring solution to a boil.

5. After boiling the solution for five minutes,carefully remove the evaporating dishusing heat-resistant gloves. Touch thedrops of liquid on the bottom of the dishto a piece of white paper.

6. Observe the liquid on the paper.

7. Think Critically In your Science Journal,write a paragraph explaining where theliquid came from. What was in the beakerthat is not in the liquid on the paper?

Demonstrate the Distillation of WaterMatter is classified according to the differentproperties that it exhibits. These differencesin properties allow drinking water to beobtained from seawater. These propertiescould be very important to you if you werestranded on a desert island and neededdrinking water. Purified water can beobtained through a process called distillation.

Preview this chapter’s contentand activities at gpscience.com

Elements MixturesCompounds

(bkgd.)Michael Newman/PhotoEdit, Inc., (inset)Matt Meadows

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450 CHAPTER 15 Classification of Matter

Composition of Matter

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Pure SubstancesHave you ever seen a picture hanging on a wall that looked

just like a real painting? Did you have to touch it to find out? Ifso, the rough or smooth surface told you which it was. Eachmaterial has its own properties. The properties of materials canbe used to classify them into general categories.

Materials are made of a pure substance or a mixture of sub-stances. A pure substance, or simply a substance, is a type ofmatter with a fixed composition. A substance can be either anelement or a compound. Some substances you might recognizeare helium, aluminum, water, and salt.

Elements All substances are built from atoms. If all the atomsin a substance have the same identity, that substance is anelement. The graphite in your pencil point and the copper coat-ing of most pennies are examples of elements. In graphite all theatoms are carbon atoms, and in a copper sample, all the atomsare copper atoms. The metal substance beneath the copper inthe penny is another element—zinc. About 90 elements arefound on Earth. More than 20 others have been made in labora-tories, but most of these are unstable and exist only for shortperiods of time. Some elements you might recognize are shownin Figure 1. Some less common elements and their propertiesare shown in Figure 2.

Reading Guide

■ Define substances and mixtures.■ Identify elements and

compounds.■ Compare and contrast solutions,

colloids, and suspensions.

You can form a better picture of your world when you understandthe concepts of elements andcompounds.

Review Vocabularyproperty: characteristic oressential quality

New Vocabulary

• substance

• element

• compound

• heterogeneous mixture

• homogeneous mixture

• solution

• colloid

• Tyndall effect

• suspension

(t)Siede Pries/PhotoDisc, (c)Ryan McVay/PhotoDisc, (b)PhotoDisc

NGS TITLE

Figure 2

VISUALIZING ELEMENTS

SECTION 1 Composition of Matter 451

Most of us think of gold as a shinyyellow metal used to make jewelry.However, it is an element that is

also used in more unexpected ways, such asin spacecraft parts. On the other hand, someless common elements, such as americium(am uh REE see um), are used in everydayobjects. Some elements and their uses areshown here.

TITANIUM (tie TAY nee um) Parts of theexterior of the Guggenheim Museum in Bilbao,Spain, are made of titanium panels. Strongand lightweight, titanium is also used for body implants.

▼

LEAD Because lead has a high density, it is a good barrier to radiation. Dentists drape leadaprons on patients before taking X rays of thepatient’s teeth to reduce radiation exposure.

▼

GOLD Gold’s resistance to corrosion and its ability to reflect infrared radiation make it an excellent coatingfor space vehicles. The electronic box on the six-wheelSojourner Rover, above, part of NASA’s Pathfinder 1997mission to Mars, is coated with gold.

▼

ALUMINUM Aluminumis an excellent reflector ofheat. Here, an aluminumplastic laminate is used toretain the body heat of anewborn baby.

▼

TUNGSTEN Althoughtungsten can be com-bined with steel to forma very durable metal, in its pure form it is softenough to be stretchedto form the filament of alightbulb. Tungsten hasthe highest meltingpoint of any metal.

▼

AMERICIUM Named afterAmerica, where it was first produced, americium is a com-ponent of this smoke detector.It is a radioactive metal thatmust be handled with care toavoid contact.

▼

(tl)James L. Amos/CORBIS, (tr)Stockbyte/PictureQuest, (cl)Yann Arthus-Bertrand/CORBIS, (cr)CalTech, (bl)Robert Fried/Stock Boston/PictureQuest, (br)Dorling Kindersley


Compounds Two or more elements can combine to form sub-stances called compounds. A compound is a substance in whichthe atoms of two or more elements are combined in a fixed pro-portion. For example, water is a compound in which two atomsof the element hydrogen combine with one atom of the element oxygen. Chalk contains calcium, carbon, andoxygen in the proportion of one atom of calcium and carbon tothree atoms of oxygen.

How are elements and compounds related?

Can you imagine yourself putting somethingmade from a silvery metal and a greenish-yellow,poisonous gas on your food? You might haveshaken some on your food today—table salt is achemical compound that fits this description.Even though it looks like white crystals and addsflavor to food, its components—sodium andchlorine—are neither white nor salty, as shownin Figure 3. Like salt, compounds usually lookdifferent from the elements in them.

Mixtures Are pizza and a soft drink one of your favorite lunches? If so,

you enjoy two foods that are classified as mixtures—but two dif-ferent kinds of mixtures. A mixture, such as the pizza or softdrink shown in Figure 4, is a material made up of two or moresubstances that can be easily separated by physical means.

Figure 3 Chlorine gas andsodium metal combine dramati-cally in the ratio of one to one toform sodium chloride.

Figure 4 Pizza and softdrinks, like most foods, aremixtures.

Chlorine(gas)

Sodium(metal)

Sodium chloride(salt)

(t)Richard Megna/Fundamental Photographs, (b)Icon Images


Heterogeneous Mixtures Unlike compounds, mixtures donot always contain the same proportions of the substances thatmake them up—the pizza chef doesn’t measure precisely howmuch of each topping is sprinkled on. You easily can see most ofthe toppings on a pizza. A mixture in which different materialscan be distinguished easily is called a heterogeneous (he tuh ruhJEE nee us) mixture. Granite, concrete, and dry soup mixes areother heterogeneous mixtures you can recognize.

You might be wearing another heterogeneous mixture—clothing made of permanent-press fabric like that seen in Figure 5A. Such fabric contains fibers of two materials—poly-ester and cotton. The amounts of polyester and cotton can varyfrom one article of clothing to another, as shown by the label.Though you might not be able to distinguish the two fibers justby looking at them with your naked eye, you probably could tellusing a microscope, as shown in Figure 5B. Therefore, a perma-nent-press fabric is also a heterogeneous mixture.

Most of the substances you come in contact with every dayare heterogeneous mixtures. Some components are easy to see,like the ingredients in pizza, but others are not. In fact, the com-ponent you see can be a mixture itself. For example, the cheesein pizza is also a mixture, but you cannot see the individualcomponents. Cheese contains many compounds, such as milkproteins, butterfat, colorings, and other food additives.

Separating MixturesProcedure1. Put equal amounts of soil,

clay, sand, gravel, andpebbles in a clear-plasticcontainer. Add water untilthe container is almost full.Wash your hands well afterhandling the materials.

2. Stir or shake the mixturethoroughly. Predict theorder in which the materialswill settle.

3. Observe what happens andcompare your observationsto your predictions.

Analysis1. In what order did the

materials settle?2. Explain why the materials

settled in the order they did.

With a microscopehowever, the differencebetween the two fibers isclear—the polyester fiberis perfectly smooth and thecotton is rough.

Cotton fiber

Polyester fiber

Figure 5 Heterogeneousmixtures can be hard to detect.

You can’t tell at a glancethat this fabric is a mixture ofcotton and polyester.

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Homogeneous Mixtures Remember that softdrink you had with your pizza? Soft drinks containwater, sugar, flavoring, coloring, and carbon dioxidegas. Figure 6 will help you to visualize these particles ina liquid soft drink.

Soft drinks in sealed bottles are examples of homoge-neous mixtures. A homogeneous (hoh muh JEE nee us)mixture contains two or more gaseous, liquid, or solidsubstances blended evenly throughout. However, a softdrink in which you can see bubbles of carbon dioxide gasand ice cubes is a heterogeneous mixture.

Vinegar is another homogeneous mixture. Itappears clear even though it is made up of particles ofacetic acid mixed with water. Another name for homo-

geneous mixtures like vinegar and a cold soft drink is solution. Asolution is a homogeneous mixture of particles so small thatthey cannot be seen with a microscope and will never settle to thebottom of their container. Solutions remain constantly and uni-formly mixed. The differences between substances and mixturesare summarized in Figure 7.

What kind of mixture is a solution?

Colloids Milk is an example of a specific kind of mixturecalled a colloid. Like a heterogeneous mixture, it containswater, fats, and proteins in varying proportions. Like a solu-tion, its components won’t settle if left standing. A colloid

(KAH loyd) is a type ofmixture with particlesthat are larger than thosein solutions but not heavyenough to settle out. Theword colloid comes from aGreek word for glue. Thefirst colloids studied werein gelatin, a source ofsome types of glue.

Paint is an example of aliquid with suspended col-loid particles. Gases andsolids can contain colloidalparticles, too. For example,fog consists of particles ofliquid water suspended inair, and smoke containssolids suspended in air.

MatterHas mass and takes

up space

ElementOne kindof atom

CompoundTwo or more

kinds of atoms

HomogeneousEvenly mixed;

a solution

HeterogeneousUnevenly

mixed

SubstanceComposition

definite

MixtureComposition

variable

Figure 6 A soft drinkcan be either heteroge-neous or homogeneous. As carbon dioxide fizzesout it is a heterogeneousmixture.

The resulting flat soft drink is ahomogeneous mixture of water,sugar, flavor, color, and someremaining carbon dioxide.

Figure 7 All matter can bedivided into substances andmixtures.

(t)Icon Images , (bl)PhotoDisc, (br)C. Squared Studios/PhotoDisc


Detecting Colloids One way to distinguish a colloid from asolution is by its appearance. Fog appears white because its par-ticles are large enough to scatter light as shown in Figure 8.Sometimes it is not so obvious that a liquid is a colloid. Forexample, some shampoos and gelatins are colloids called gelsthat appear almost clear. You can tell for certain if a liquid is acolloid by passing a beam of light through it, as shown in Figure 9. A light beam is invisible as it passes through a solution,but can be seen readily as it passes through a colloid. This occursbecause the particles in the colloid are large enough to scatterlight, but those in the solution are not. This scattering of light bycolloidal particles is called the Tyndall effect.

How can you distinguisha colloid from a solution?

Figure 9 Because of the Tyndalleffect, a light beam is scattered bythe colloid suspension on the right,but passes invisibly through thesolution on the left.

Figure 8 Fog is a col-loid composed of waterdroplets suspendedin air.

The same colloid allows you to seethe sunlight as it streams throughthe trees.

The light from the head-lights is scattered by fog.

(tl)Chuck Keeler, Jr./The Stock Market/CORBIS, (tr)Kaj R. Svensson/Science Photo Library/Photo Researchers, (b)Kip & Pat Peticolas/Fundamental Photographs

456 CHAPTER 15 Classification of Matter gpscience.com/self_check

Self Check1. Describe How is a compound similar to a homoge-

neous mixture? How is it different?

2. Distinguish between a substance and a mixture. Givetwo examples of each.

3. Describe the differences between colloids andsuspensions.

4. Think Critically Why do the words “Shake well beforeusing” indicate that the fruit juice is a suspension?

SummaryPure Substances

• An element is a substance in which all atomshave the same identity.

• A compound is a substance that has two ormore elements combined in a fixed proportion.

Mixtures

• Heterogeneous mixtures are mixtures in whichdifferent materials can be distinguished easily.

• A homogeneous mixture contains two ormore gaseous, liquid, or solid substances thatare blended evenly throughout.

• Mixtures can be heterogeneous, homoge-neous, colloids, or suspensions.

Figure 10 The mud depositedby the Mississippi River is said tobe more than 10,000 m thick.

5. Compare and Contrast In terms of suspensions andcolloids, compare and contrast a glass of milk and a glass of fresh-squeezed orange juice.

Suspensions Some mixtures are neither solutions nor colloids.One example is muddy pond water. If pond water stands longenough, some mud particles will fall to the bottom, and the waterclears. Pond water is a suspension, which is a heterogeneous mix-ture containing a liquid in which visible particles settle. Table 1summarizes the properties of different types of mixtures.

River deltas are a large scale example of howa suspension settles. Rivers flow swiftly

through narrow channels, picking up soil and debris along theway. As the river widens, it flows more slowly. Suspended particlessettle forming deltas at the mouth, as shown in Figure 10.

Table 1 Comparing Solutions, Colloids, and Suspensions

Description Solutions Colloids Suspensions

Settle upon no no yes standing?

Separate using no no yes filter paper?

Particle size 0.1–1 nm 1–100 nm >100 nm

Scatter light? no yes yes

Larry Mayer/Liaison Agency/Getty Images

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LAB 457

Elements, compounds, and mixtures all containatoms. In elements, the atoms all have thesame identity. In compounds, two or more ele-ments have been combined in a fixed ratio.In mixtures, the ratio of substances can vary.

Real-World QuestionWhat are some differences among elements,compounds, and mixtures?

Goals■ Determine whether several materials are

elements, compounds, or mixtures.

Materialsplastic freezer bag containing the followinglabeled items:copper wire chalk (calcium small package of salt carbonate)pencil piece of granitealuminum foil sugar water in a vial

Safety Precautions

Procedure1. Copy the data table into your Science Journal

and use it to record your observations.

2. Obtain a bag of objects. Identify each objectand classify it as an element, compound,heterogeneous mixture, or homogeneousmixture. The elements appear in the periodictable. Compounds are named as examples inSection 1.

Conclude and Apply1. If you know the name of a substance, how can

you find out whether or not it is an element?

2. Examine the contents of your refrigeratorat home. Classify what you find as elements,compounds, or mixtures.

3. Identify whether the mixtures are homo-geneous or heterogeneous, and whetherthey are colloids or suspensions.

Elements, Compounds, and Mixtures

Classification of Objects

Object Identity Classification

1

2

3

4

5

6

7

Enter your data in the data table and compare your findings with those of yourclassmates. For more help, refer to theScience Skill Handbook.

Icon Images

Physical PropertiesYou can stretch a rubber band, but you can’t stretch a piece

of string very much, if at all. You can bend a piece of wire, butyou can’t easily bend a matchstick. In each case, the materialschange shape, but the identity of the substances—rubber, string,wire, wood—does not change. The abilities to stretch and bendare physical properties. Any characteristic of a material that youcan observe without changing the identity of the substances thatmake up the material is a physical property. Examples of otherphysical properties are color, shape, size, density, melting point,and boiling point. What physical properties can you use todescribe the items in Figure 11?

Appearance How would you describe a tennis ball? Youcould begin by describing its shape, color, and state of matter.For example, you might describe the tennis ball as a brightlycolored, hollow sphere. You can measure some physical prop-erties, too. For instance, you could measure the diameter ofthe ball. What physical property of the ball is measured with abalance?

To describe a soft drink in a cup, you could start by calling ita liquid with a brown color. You could measure its volume andtemperature. Each of these characteristics is a physical propertyof that soft drink.

Properties of Matter

Figure 11 Appearance is themost obvious physical property. Describe the appearance of these items.


Reading Guide

■ Identify substances using physi-cal properties.

■ Compare and contrast physicaland chemical changes.

■ Identify chemical changes. ■ Determine how the law of con-

servation of mass applies tochemical changes.

Understanding chemical and physicalproperties can help you use materialsproperly.

Review Vocabularystate of matter: one of three physi-cal forms of matter—solid, liquid,or gas

New Vocabulary

• physical property

• physical change

• distillation

• chemical property

• chemical change

• law of conservation of mass

Matt Meadows

SECTION 2 Properties of Matter 459

Behavior Some physical properties describe the behavior of amaterial or a substance. As you might know, objects that containiron, such as a safety pin, are attracted by a magnet. Attractionto a magnet is a physical property of the substance iron. Everysubstance has a specific combination of physical properties thatmake it useful for certain tasks. Some metals, such as copper, canbe drawn out into wires. Others, such as gold, can be poundedinto sheets as thin as 0.1 micrometers (µm), about 4-millionthsof an inch. This property of gold makes it useful for decoratingpicture frames and other objects. Gold that has been beaten orflattened in this way is called gold leaf.

Think again about your soft drink. If you knock over thecup, the drink will spread out over the table or floor. If youknock over a jar of molasses, however, it does not flow as easily.The ability to flow is a physical property of liquids.

Using Physical Properties to Separate Removing theseeds from a watermelon can be easily done based on the phys-ical properties of the seeds compared to the rest of the fruit.Figure 12 shows a mixture of poppy seeds and sunflower seeds.You can identify the two kinds of seeds by differences in color,shape, and size. By sifting the mixture, you can separate thepoppy seeds from the sunflower seeds quickly because their sizesdiffer.

Now look at the mixture of iron filings and sand shown inFigure 12. You probably won’t be able to sift out the iron filingsbecause they are similar in size to the sand particles. What youcan do is pass a magnet through the mixture. The magnetattracts only the iron filings and pulls them from the sand. Thisis an example of how a physical property, such as magneticattraction, can be used to separate substances in a mixture.Something like this is done to separate iron for recycling.

Figure 12 The bestway to separate sub-stances depends on theirphysical properties. Size is the property used toseparate poppy seedsfrom sunflower seeds inthis example.

Recycling and PhysicalProperties Recycling con-serves natural resources. Insome large recycling proj-ects, aluminum metal mustbe separated from scrapiron. What physical proper-ties of the two metals couldbe used to separate them?

Magnetism easily separates ironfrom sand.

(t)Amanita Pictures, (b)Doug Martin


Physical ChangeIf you break a piece of chewing gum, you change some of its

physical properties—its size and shape. However, you have notchanged the identity of the materials that make up the gum.

The Identity Remains the Same When a substancefreezes, boils, evaporates, or condenses, it undergoes physicalchanges. A change in size, shape, or state of matter is called aphysical change. These changes might involve energy changes,but the kind of substance—the identity of the element or com-pound—does not change. Because all substances have distinctproperties like densities, specific heats, and boiling and meltingpoints, which are constant, these properties can be used to helpidentify them when a particular mixture contains substanceswhich are not yet identified.

Does a change in state mean that a new substance has formed? Explain.

Iron is a substance that can change states if it absorbs or releasesenough energy—at high temperatures, it melts. However, in boththe solid and liquid state, iron has physical properties that identifyit as iron. Color changes can accompany a physical change, too. Forexample, when iron is heated it first glows red. Then, if it is heatedto a higher temperature, it turns white, as shown in Figure 13.

Using Physical Change to Separate A cool drink ofwater is something most people take for granted, but in someparts of the world, drinkable water is scarce. Not enough drink-able water can be obtained from wells. Many such areas that lieclose to the sea obtain drinking water by using physical propertiesof water to separate it from the salt. One of these methods, whichuses the property of boiling point, is a type of distillation.

Figure 13 Heating iron raisesits energy level and changes itscolor. These energy changes arephysical changes because it isstill iron.

Identifying Changes Procedure

WARNING: Clean up any spillspromptly. Potassiumpermanganate can stainclothing.1. Add water to a 250-mL

beaker until it is half-full.2. Add a crystal of potassium

permanganate to thewater and observe whathappens.

3. Add 1 g of sodium hydro-gen sulfite to the solutionand stir it until the solutionbecomes colorless.

Analysis1. Is dissolving a chemical or

a physical change?2. What evidence of a chemi-

cal change did you see?

Richard Megna/Fundamental Photographs

Distillation The process for separatingsubstances in a mixture by evaporating aliquid and recondensing its vapor isdistillation. It usually is done in thelaboratory using an apparatus similar tothat shown in Figure 14. As you can see,the liquid vaporizes and condenses, leav-ing the solid material behind.

Two liquids having different boilingpoints can be separated in a similar way.The mixture is heated slowly until it beginsto boil. Vapors of the liquid with the lowestboiling point form first and are condensedand collected. Then, the temperature isincreased until the second liquid boils, con-denses, and is collected. Distillation is usedoften in industry. For instance, natural oilssuch as mint are distilled.

Chemical Properties and ChangesYou probably have seen warnings on cans of paint thinners

and lighter fluids for charcoal grills that say these liquids areflammable (FLA muh buhl). The tendency of a substance toburn, or its flammability, is an example of a chemical propertybecause burning produces new substances during a chemicalchange. A chemical property is a characteristic of a substancethat indicates whether it can undergo a certain chemical change.Many substances used around the home, such as lighter fluids,are flammable. Knowing which ones are flammable helps you touse them safely.

A less dramatic chemical change can affect some medicines.Look at Figure 15. You probably have seen bottles like this in apharmacy. Many medicines are stored in dark bottles becausethey contain compounds that can change chemically if they areexposed to light.

Coolingwater out

Distillingflask withimpure liquid

Condenser

Pure liquid

Thermometer

Coolingwater in

Figure 15 The brown color ofthese bottles tells you that thesevitamins may react to light.Reaction to light is a chemicalproperty.


Figure 14 Distillation can easily separate liquids from solidsdissolved in them. The liquid is heated until it vaporizes andmoves up the column. Then, as ittouches the water-cooled surfaceof the condenser, it becomes liquid again.

Jed & Kaoru Share/Stone/Getty Images


Detecting Chemical ChangeIf you leave a pan of chili cooking unattended on the stove

for too long, your nose soon tells you that something is wrong.Instead of a spicy aroma, you detect an unpleasant smell thatalerts you that something is burning. This burnt odor is a cluetelling you that a new substance has formed.

The Identity Changes The smell of rotten eggs and the for-mation of rust on bikes or car fenders are signs that a chemicalchange has taken place. A change of one substance to another isa chemical change. The foaming of an antacid tablet in a glassof water and the smell in the air after a thunderstorm are othersigns of new substances being produced. In some chemicalchanges, a rapid release of energy—detected as heat, light, andsound—is a clue that changes are occurring.

What is a chemical change?

Clues such as heat, cooling, or the formation of bubbles orsolids in a liquid are helpful indicators that a reaction is takingplace. However, the only sure proof is that a new substance isproduced. Consider the following example. The heat, light, andsound produced when hydrogen gas combines with oxygen in arocket engine are clear evidence that a chemical reaction hastaken place. But no clues announce the reaction that takes placewhen iron combines with oxygen to form rust because the reac-tion takes place so slowly. The only clue that iron has changedinto a new substance is the presence of rust. Burning and rustingare chemical changes because new substances form. You some-times can follow the progress of a chemical reaction visually. Forexample, you can see lead nitrate forming in Figure 16.

Figure 16 The solid formingfrom two liquids is another signthat a chemical reaction has takenplace.

Alchemy In the MiddleAges, alchemy was anearly form of chemistrydevoted to the studyof changing baser metalsinto gold and also to find-ing the elixir of perpetualyouth. Based on what weknow now about theproperties of metalsand biology, it is easyto understand why thisfield of study is no longerpracticed.

Richard Megna/Fundamental Photographs


Using Chemical Change to Separate One case whereyou might separate substances using a chemical change is incleaning tarnished silver. Tarnish is a chemical reaction betweensilver metal and sulfur compounds in the air which results in sil-ver sulfide. It can be changed back into silver using a chemicalreaction. This chemical reversal back to silver takes place whenthe tarnished item is placed in a warm water bath with bakingsoda and aluminum foil. You don’t usually separate substancesusing chemical changes in the home. In industry and chemicallaboratories, however, this kind of separation is common. Forexample, many metals are separated from their ores and thenpurified using chemical changes.

Calculate

1. In the following reaction, 24 g of CH4 (methane) react completely with 96 g of O2 to

form 66 g of CO2. How many grams of H2O are formed? CH4 � 2O2 → CO2 � 2H2O

2. In the following equation, 54.0 g of Al react completely with 409.2 g of ZnCl2 to form

196.2 g of Zn metal. How many grams of AlCl3 are formed? 2Al � 3ZnCl2 → 3Zn � 2AlCl3For more practice problems, go to page 834, and visit gpscience.com/extra_problems.

CALCULATIONS WITH THE LAW OF CONSERVATION OF MASS When a chemical reaction takes place, the

total mass of reactants equals the total mass of products. If 18 g of hydrogen react completely with

633 g of chlorine, how many grams of HCl are formed? H2 � Cl2 → 2HCl

known values and the unknown value

Identify the known values:

mass of H2 � 18 g

mass of Cl2 � 633 g

mass of reactants � mass of products

Identify the unknown value:

mass of HCl ? g

the problem

Solve for the mass of HCl. g H2�g Cl2 � g HCl

Substitute the known values. 18 g � 633 g � 651 g HCl

your answer

Does your answer seem reasonable? Check your answer by subtracting the mass of H2 from the

mass of HCl. Do you obtain the mass of the Cl2? If so, the answer is correct.

CHECK

SOLVE

means

IDENTIFY

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Weathering—Chemical or Physical Change?

The forces of nature continuously shape Earth’s surface.Rocks split, deep canyons are carved out, sand dunes shift, andcurious limestone formations decorate caves. Do you thinkthese changes, often referred to as weathering, are physical orchemical? The answer is both. Geologists, who use the same cri-teria that you have learned in this chapter, say that some weath-ering changes are physical and some are chemical.

Physical Large rocks can split when water seeps into smallcracks, freezes, and expands. However, the smaller pieces ofnewly exposed rock still have the same properties as the originalsample. This is a physical change. Streams can cut through softerrock, forming canyons, and can smooth and sculpt harder rock,as shown at left in Figure 17. In each case, the stream carriesrock particles far downstream before depositing them. Becausethe particles are unchanged, the change is a physical one.

Chemical In other cases, the change is chemical. For example,solid calcium carbonate, a compound found in limestone, doesnot dissolve easily in water. However, when the water is evenslightly acidic, as it is when it contains some dissolved carbondioxide, calcium carbonate reacts. It changes into a new sub-stance, calcium hydrogen carbonate, which does dissolve inwater. This change in limestone is a chemical change because theidentity of the calcium carbonate changes. The White Cliffs ofDover, shown at right in Figure 17, are made of limestone andundergo such chemical changes, as well as physical changes. Asimilar chemical change produces caves and the icicle-shapedrock formations that often are found in them.

Figure 17 Weathering caninvolve physical or chemicalchange.

Flowing water shaped and smoothed theserocks in a physical process.

Both chemical and physical changes shaped the famousWhite Cliffs of Dover lining the English Channel.

Topic: CavesVisit gpscience.com for Web linksto information about caveformations.

Activity Describe the formationof stalactites and stalagmites.Explain the differences betweenthe two and whether they are theresult of a physical and/or chemicalprocess.

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Self Check1. Explain why evaporation of water is a physical change

and not a chemical change.

2. List four physical properties you could use to describe a liquid.

3. Describe why flammability is a chemical propertyrather than a physical property.

4. Explain how the law of conservation of mass applies tochemical changes.

5. Think Critically How might you demonstrate this lawof conservation of mass for melting ice and distillationof water?

SummaryPhysical Properties

• You can observe physical properties withoutchanging the identity of a substance.

Physical Change

• Change in the size, shape, or state of matter isa physical change.

Chemical Properties and Changes

• A chemical property is a characteristic of asubstance that indicates whether it canundergo a certain chemical change.

• A change of one substance to another is achemical change.

• Many metals are separated from their oresand purified using chemical changes.

The Conservation of Mass Wood is combustible, or burnable. As you just

learned, this is a chemical property. Suppose you burna large log in the fireplace, as shown in Figure 18,until nothing is left but a small pile of ashes. Smoke,heat, and light are given off and the changes in theappearance of the log confirm that a chemical changetook place. At first, you might think that matter waslost during this change because the pile of ashes looksmuch smaller than the log did. In fact, the mass of theashes is less than that of the log. However, supposethat you could collect all the oxygen in the air thatwas combined with the log during the burning and all the smokeand gases that escaped from the burning log and measure theirmasses, too. Then you would find that no mass was lost after all.

Not only is no mass lost during burning, mass is not gainedor lost during any chemical change. In other words, matter isneither created nor destroyed during a chemical change.According to the law of conservation of mass, the mass of allsubstances that are present before a chemical change equals themass of all the substances that remain after the change.

Explain what is meant by the law of conservation of mass.

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Figure 18 This reaction appearsto be destroying these logs. Whenit is over, only ashes will remain.Yet you know that no mass is lostin a chemical reaction. Explain why this is so.

6. Calculate In the following equation, 417.96 g of Bi(bismuth) react completely with 200 g of F (fluorine).How many grams of BiF3 (bismuth fluoride) are formed? 2 Bi � 3 F2 0 2 BiF3

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Real-World QuestionMixing materials together does not always produce a chemicalchange. You must find evidence of a new substance with new proper-ties being produced before you can conclude that a chemical changehas taken place. Try this lab and use your observation skills to deducewhat kind of change has occurred. What evidence indicates a chemicalchange?

Form a HypothesisThink about what happens when small pieces of limestone are mixedwith sand. What happens when limestone is mixed with an acid?Based on these thoughts, form a hypothesis about how to determinewhen mixing substances together produces a chemical change.

Test Your HypothesisMake a Plan1. As a group, agree upon a hypothesis and decide how to test it.

Write the hypothesis statement.

2. To test your hypothesis, devise a plan to compare two differentmixtures. The first mixture consists of 3 mL of hydrochloric acidand 0.5 g of baking soda. The second mixture is 3 mL of hydrochlo-ric acid and the solid product of the first mixture. Describe exactlywhat you will do at each step.

Checking Out ChPmical Changes

Limestone Sand

Goals■ Observe the results

of adding dilutehydrochloric acid tobaking soda.

■ Infer that the produc-tion of new substancesindicates that a chemi-cal change has occurred.

■ Design an experimentthat allows you to com-pare the activity of baking soda with that ofa product formed whenbaking soda reacts.

Possible Materials baking sodasmall evaporating dishmagnifying lens1M hydrochloric acid (HCl)10-mL graduated cylinder electric hot plate

Safety Precautions

Icon Images

LAB 467

3. Make a list of the materials needed to complete yourexperiment.

4. Design a table for data and observations in yourScience Journal so that it is ready to use as yourgroup observes what happens.

Follow Your Plan1. Make sure your teacher approves your plan before

you start.

2. Read over your entire experiment to make sure thatall steps are in logical order.

3. Identify any constants and the variables of theexperiment.

4. Should you run any test more than once? How willobservations be summarized?

5. Assemble your materials and carry out the experi-ment according to your plan. Be sure to record yourresults as you work.

Analyze Your Data1. Observe what happened to the baking soda. Did anything happen to the

product formed from the first mixture? Explain why this occurred.

2. Describe What different properties of any new substances did you observeafter adding hydrochloric acid to the baking soda?

Conclude and Apply1. Did the results support your hypothesis? Explain.

2. If you had used vinegar, which contains acetic acid, as the acid, do youthink a new susbstance would have formed? How could you test this?

Write a description of your observations inyour Science Journal. Compare your resultswith those of other groups. Discuss yourconclusions.

(t)Icon Images, (b)Matt Meadows

Intriguing ElementsDid you know…


… Zinc makes chewing gumtaste better. Up to 0.3 mg of zinc acetatecan be added per 1,000 mg of chewinggum to provide a tart, zingy flavor.

… Silver-white cobalt, which usually is combined withother elements in nature, is used to create rich paint pigments.It can be used to form powerful magnets, treat cancer patients,build jet engines, and prevent disease in sheep.

… Gold is the most ductile(stretchable) of all the elements.Just 29 g of gold—about tenwedding bands—can be pulledinto a wire 100 km long. That’slong enough tostretch fromToledo, Ohio,to Detroit,Michigan,and beyond.

1. Zinc acetate is approximately 35% zinc. How many grams ofchewing gum would be needed to provide a total of 10.0 mg of zinc?

2. If you wanted to produce a gold wire as mentioned in our example,how many grams would be needed to make a wire one kilometer inlength?

3. Table sugar has the chemical formula C12H22O11. If you were going tobuild a scale model of sucrose (table sugar) and you had 36 carbonmodel atoms, how many of each of the others (hydrogen and oxygen)would you need to build an accurate, complete sucrose model?

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Composition of Matter

1. Elements and compounds are substances.A mixture is composed of two or more sub-stances.

2. You can distinguish between the differentmaterials in a heterogeneous mixture usingeither your unaided eyeor a microscope.

3. Colloids and suspensionsare two types of hetero-geneous mixtures. Theparticles in a suspensionwill settle eventually.Particles of a colloid willnot. Milk is an exampleof a colloid.

4. In a homogeneous mix-ture, the particles are dis-tributed evenly and arenot visible, even whenusing a microscope. Homogeneous mixturescan be composed of solids, liquids, or gases.

5. A solution is another name for a homoge-neous mixture that remains constantly anduniformly mixed.

This is a clear indication that this is asuspension.

Properties of Matter

1. Physical properties are characteristics ofmaterials that you can observe withoutchanging the identity of the sub-stance.

2. Chemical properties indicate what chemicalchanges substances canundergo. Manymedicines arestored in darkbottles becausethey react withlight.

3. In physical changes, the identities ofsubstances remain unchanged.

4. In chemical changes, the identities of sub-stances change—new substances are formed.There is a visible chemical change that takesplace when rust is cleaned with bleach.

5. The law of conservation of mass states that during any chemical change, matter is neither created nor destroyed.

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Use the Foldable that you made at the begin-ning of the chapter to help you review the classifications ofmatter.

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Complete each sentence with the correctvocabulary word or words.

1. Substances formed from atoms of two ormore elements are called _________.

2. A(n) _________ is a heterogeneous mixturein which visible particles settle.

3. Freezing, boiling, and evaporation are allexamples of _________.

4. According to the _________, matter isneither created nor destroyed during achemical change.

5. A mixture in which different materials areeasily identified is _________.

6. Compounds are made from the atoms oftwo or more _________.

7. Distillation is a process that can separatetwo liquids using _________.

Choose the word or phrase that best answers the question.

8. Bending a copper wire is an example ofwhat type of property?A) chemical C) conservationB) physical D) element

9. Which of the following is NOT an element?A) water C) oxygenB) carbon D) hydrogen

10. Which of the following is an example of achemical change?A) boiling C) evaporationB) burning D) melting

11. What type of substance is gelatin?A) colloid C) substanceB) compound D) suspension

12. A visible sunbeam is an example of whichof the following?A) an element C) a compoundB) a solution D) the Tyndall effect

13. You start to eat some potato chips from anopen bag you found in your locker andnotice that they taste unpleasant. What doyou think might cause this unpleasant taste? A) combustion C) physical changeB) melting D) chemical change

14. How would you classify the color of a rose?A) chemical change C) chemical propertyB) physical change D) physical property

15. How would you describe the process ofevaporating water from seawater?A) chemical change C) chemical propertyB) physical change D) physical property

16. Which of these warnings refers to a chem-ical property of the material?A) Fragile C) Handle with CareB) Flammable D) Shake Well

17. Which of the following is a substance?A) colloid C) mixtureB) element D) solution

18. Which of these properties can be used tohelp identify an unknown substance?A) specific heat C) temperatureB) combustion D) Tyndall effect

470 CHAPTER REVIEW gpscience.com/vocabulary_puzzlemaker

chemical change p. 462chemical property p. 461colloid p. 454compound p. 452distillation p. 461element p. 450heterogeneous mixture

p. 453homogeneous mixture

p. 454

law of conservation ofmass p. 465

physical change p. 460physical property p. 458solution p. 454substance p. 450suspension p. 456Tyndall effect p. 455

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19. Copy and complete the concept mapbelow about matter.

Use the table below to answer question 20.

20. Different colloids can involve differentstates. For example, gelatin is formed fromsolid particles in a liquid. Complete thistable using these colloids: smoke, marsh-mallow, fog, and paint.

21. Describe the contents of a carton of milkusing at least four physical properties.

22. Explain Carbon and the gases hydrogenand oxygen combine to form sugar. Howdo you know sugar is a compound?

23. Explain The word colloid means “gluelike.”Why was this term chosen to name certainmixtures?

24. Use a nail rusting in air to explain the lawof conservation of mass.

25. Explain Mai says that ocean water is a solu-tion. Tom says that it’s a suspension. Canthey both be correct? Explain.

26. Use Variables, Constants, and Controls Marcostook a 100-cm3 sample of a suspension,shook it well, and poured equal amountsinto four different test tubes. He placed onetest tube in a rack, one in hot water, one inwarm water, and the fourth in ice water. Hethen observed the time it took for each sus-pension to settle. What was the variable inthe experiment? What was one constant?

27. Concept Map Make a network tree to showtypes of liquid mixtures. Include theseterms: homogeneous mixtures, heterogeneousmixtures, solutions, colloids, and suspensions.

Common Colloids

Colloid Example

Solid in a liquid Gelatin

Solid in a gas

Gas in a solid

Solid in a liquid

Liquid in a gas

CHAPTER REVIEW 471gpscience.com/chapter_review

28. Interpret Data Hannah started with a 25-mL sample of pond water. Withoutshaking the sample, she poured 5 mLthrough a piece of filter paper. Sherepeated this with four more pieces offilter paper. She dried each piece of fil-ter paper and measured the mass of thesediment. Why did the last sample havea higher mass than did the first sample?

29. Use Numbers In the following equation,243.5 g of Sb (antimony) react completelywith 1000 g of I2 (iodine) to form1004.9 g of SbI3 (antimony triiodide).How many grams of I2 were consumedin the reaction? 2 Sb � 3 I2 → 2 SbI3

Matter

Substance

Homogeneous

can be a can be a

can be a(n)can be a(n) can be can be

an example is an example is an example is an example is

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Record your answers on the answer sheetprovided by your teacher or on a sheet of paper.

1. Which statement about elements is FALSE?A. All atoms in an element are alike.B. There are about 1,000 elements found in

nature.C. Some elements have been made in

laboratories.D. Zinc, copper, and iron are elements.

2. CaCO3 is an example of which type ofmaterial?A. element C. compoundB. mixture D. colloid

Use the graph below to answer questions 3 and 4.

3. What percentage do the elements hydrogenand helium account for in the universe?A. 100% C. 98%B. 99.9% D. 99.8%

4. The most plentiful element in the universereadily burns in air. What is this chemicalproperty called?A. flammabilityB. ductilityC. densityD. boiling point

Use the graph below to answer questions 5 and 6.

5. Which element makes up 8 percent ofEarth’s crust?A. iron C. siliconB. aluminum D. oxygen

6. Which element has the physical property ofmagnetism?A. sodium C. oxygenB. iron D. calcium

7. Which statement best decribes the law ofconservation of mass?A. The mass of the products is always

greater than the mass of the materialswhich react in a chemical change.

B. The mass of the products is always lessthan the mass of the materials whichreact in a chemical change.

C. A certain mass of material must be pres-ent for a reaction to occur.

D. Matter is neither lost nor gained duringa chemical change.

Perc

ent

of c

rust

2030

5040

100

Si Al CaO Fe Na K Mg Others

Elements in Earth’s Crust

ElementsElements in the Universe

Hydrogen93.5%

Helium6.3%

Otherelements

0.2%

472 STANDARDIZED TEST PRACTICE

Directions and Instructions Listen carefully to theinstructions from the teacher and read the directions and eachquestion carefully.

STANDARDIZED TEST PRACTICE 473gpscience.com/standardized_test

Record your answers on the answer sheetprovided by your teacher or on a sheet of paper.

Use the illustrations below to answer questions 8 and 9.

8. What physical properties could be used toidentify these minerals?

9. Describe some ways these minerals, orrocks which contain these minerals, areweathered in nature.

10. Why are some medicines stored in darkbottles?

11. Describe the properties of tungsten whichmake it a useful material. How do you usethis element daily?

12. What physical and chemical properties ofgold make it useful as a coating for spacevehicles?

13. Compare and contrast the properties ofheterogeneous and homogeneous mix-tures. What is another name for ahomogeneous mixture?

14. You are given a mixture of iron filings,sand, and salt. Describe how to separatethis mixture.

Record your answers on a sheet of paper.

Use the illustration below to answer questions 15 and 16.

15. What indicates that more than just a phys-ical change is taking place as the woodburns?

16. Design an experiment which shows thatthis type of chemical change is governedby the law of conservation of mass.

17. Illustrate and describe the process ofdistillation of sea water using a multi-stepprocess. On what physical property is thisprocess based?

18. Explain the statement “Everything onEarth is made from 90 elements.” Doesthis surprise you? Why or why not?

19. What type of mixture is a salad dressingmade with oil, vinegar, and herbs? How doyou know?

20. Choose an object in the room anddescribe its physical properties as com-pletely as possible. Use available tools todescribe measurable properties of theobject.

21. Describe how a compound is a combina-tion of elements in a fixed proportion.Give two examples.

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