9.1 Carbon Compounds

Reading StrategyPreviewing Copy the table below. Beforeyou read, use the models in Figure 2 todescribe the arrangement of carbon atoms in each form of carbon.

Key ConceptsWhat are three formsof carbon?

What factors determinethe properties of a hydrocarbon?

What are the three types of unsaturatedhydrocarbons?

What are the three main fossil fuels and thetwo primary products of their combustion?

Vocabulary◆ organic compound◆ network solid◆ hydrocarbon◆ saturated

hydrocarbon◆ isomers◆ unsaturated

hydrocarbon◆ aromatic

hydrocarbons◆ fossil fuels

a. ?

b. ?

c. ?

Forms of Carbon Compounds

Diamond

Graphite

Buckminsterfullerene

262 Chapter 9

Until 1828, chemists divided compounds into compounds thatchemists could produce and compounds that only organisms couldproduce. The compounds produced by organisms were called organiccompounds. In 1828, a German chemist, Friedrich Wöhler, mixedsilver cyanate, AgOCN, with ammonium chloride, NH4Cl. He expectedto make ammonium cyanate. Instead, he produced urea, (NH2)2CO,which is a product of reactions that occur in the livers of many organ-isms. Wöhler had synthesized an organic compound.

An organic compound contains carbon and hydrogen, often com-bined with a few other elements such as oxygen and nitrogen. There aremillions of organic compounds—more than 90 percent of all knowncompounds. Remember that carbon has four valence electrons. So acarbon atom can form four single covalent bonds, or a double bondand two single bonds, or a triple bond and a single bond. Most of thebonds in organic compounds are carbon-to-carbon bonds or carbon-to-hydrogen bonds.

Figure 1 A whale’s survivaldepends on carbon compounds.Carbon compounds form thestructures of a whale’s cells andcontrol reactions that take placein those cells. The instructions forthese processes are stored inorganic compounds.

262 Chapter 9

FOCUS

Objectives9.1.1 Relate the structures of

three forms of carbon to their properties.

9.1.2 Explain why there are millionsof different organic compounds.

9.1.3 Relate the number andarrangement of carbon atoms in hydrocarbons to their properties.

9.1.4 Distinguish unsaturated fromsaturated hydrocarbons.

9.1.5 Classify hydrocarbons usingstructural formulas and names.

9.1.6 Describe the formation,composition, and uses of three types of fossil fuels.

9.1.7 Distinguish completecombustion from incompletecombustion of fossil fuels.

9.1.8 Describe the effects of someproducts of the combustion of fossil fuels.

Build VocabularyConcept Map Have students make aconcept map with the word hydrocarbonsas the starting point. The diagram shouldinclude the following terms: saturatedhydrocarbons, unsaturated hydrocarbons,alkanes, alkenes, alkynes, aromatic hydro-carbons, branched chain, straight chain,and rings.

Reading Strategya. Rigid three-dimensional networkb. Widely spaced layers c. Hollowspheres with a surface of carbon atomsarranged in alternating hexagons and pentagons

INSTRUCTBuild Reading LiteracyRelate Cause and Effect Refer topage 260D in this chapter, whichprovides the guidelines for relatingcause and effect.

Have students read p. 262. Ask, Whatcaused scientists to change thedefinition of an organic compound?(Wöhler synthesized urea, an organiccompound produced by many organisms.)Logical

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Reading Focus

1

Section 9.1

Print• Guided Reading and Study Workbook

With Math Support, Section 9.1 and Math Skill: Balancing Equations forOrganic Reactions

• Transparencies, Chapter Pretest andSection 9.1

Technology • iText, Section 9.1• Presentation Pro CD-ROM, Chapter Pretest

and Section 9.1• Go Online, NSTA SciLinks, Fossil fuels

Section Resources

Forms of CarbonThe element carbon exists in several forms with different properties.

Diamond, graphite, and fullerenes are forms of carbon. In eachform, there is a different arrangement of bonded carbon atoms.

Diamond Cutting, grinding, and drilling tools are often coatedwith diamond because no substance is harder than diamond. Diamondis an example of a network solid. In a network solid, all the atoms arelinked by covalent bonds. A network solid is sometimes described as asingle molecule. Figure 2A shows how the carbon atoms are linked indiamond. Covalent bonds connect each carbon atom in diamond tofour other carbon atoms. The three-dimensional structure that resultsis rigid, compact, and strong. Diamond is harder than other substancesbecause cutting a diamond requires breaking many covalent bonds.

Graphite A second form of carbon, graphite, has very differentproperties from diamond. It is extremely soft and slippery. Figure 2Bshows how the carbon atoms in graphite are arranged in widely spacedlayers. Within each layer, each carbon atom forms strong covalentbonds with three other carbon atoms. Between graphite layers thebonds are weak, which allows the layers to slide easily past one another.Because graphite is soft and slippery, it is a good lubricant for movingmetal parts in machinery. Pencil “lead” is a mixture of graphite andclay. The layered structure of graphite explains why you can makepencil marks on paper and why the marks can be erased easily.

Fullerenes In 1985, researchers discovered a third form of carbonin the soot produced when some carbon compounds burn. Fullerenesare large hollow spheres or cages of carbon. These cages have since beenfound in meteorites. Figure 2C shows a model of a cage made from60 carbon atoms. On the surface of the cage, the atoms form alternat-ing hexagons and pentagons, like a soccer ball cover. The C60 moleculeis called buckminsterfullerene after Buckminster Fuller, an architectwho designed domes with similar geometric patterns.

Figure 2 There are several formsof carbon. A In diamond, carbonatoms are arranged in a rigid,three-dimensional network. B Ingraphite, the atoms are arrangedin layers. C In fullerenes, carbonatoms are arranged in hollowspheres. Predicting Are theproperties of fullerenes more likethose of diamond or of graphite?Give a reason for your choice.

Carbon Chemistry 263

Diamond Graphite

A B

Buckminsterfullerene

CForms of CarbonUse VisualsFigure 2 Emphasize that the structuresshown in A, B, and C all contain onlycarbon atoms. Ask, What are thedifferences between the three formsof carbon? (Diamond has a rigid three-dimensional structure, graphite containswidely spaced layers, and fullerenes arehollow cages.) What types of bondshold carbon atoms together in allthree forms of carbon? (Covalent bonds)Visual

When students are asked why amethane molecule has the formula CH4, a typical response is that carbonneeds four bonds. Encourage them toconsider a less anthropomorphic view.Have students recall that carbon hasfour valence electrons and that neon haseight valence electrons. When carbonatoms form four single covalent bonds,as in methane, they achieve the stableelectron configuration of neon. Logical

FYICharcoal, carbon black, and lamp blackare classified as amorphous carbonbecause they do not have a regularcrystalline structure.

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Carbon Chemistry 263

Customize for English Language Learners

List-Group-LabelEncourage students to work independently or in groups to brainstorm words that makethem think of the following forms of carbon:diamond, graphite, and fullerenes. Then, askstudents to review the list of words and groupthem into logical categories (structure: rigid,

hollow, layers; properties: slippery, hard, soft;uses: writing, cutting, jewelry). There must beat least three words in each group. Studentscan include a word in more than one group.They should label the groups to show how the words are related.

Answer to . . .

Figure 2 Students may predict thatfullerenes are likely to have propertiesmore like diamond because of theirthree-dimensional structures. Or, theymay (correctly) predict that fullereneshave properties more like graphitebecause their hollow structures are not rigid.

264 Chapter 9

Saturated HydrocarbonsGrass contains a compound called cellulose. Most organisms,including the grazing cows in Figure 3, cannot digest cellulose.However, microorganisms in cows’ stomachs break down cellu-lose into smaller molecules that cows can digest. One of theproducts of this process is methane, CH4, which is a hydrocar-bon. A hydrocarbon is an organic compound that contains onlythe elements hydrogen and carbon. Methane is a saturated hydro-carbon. In a saturated hydrocarbon, all of the bonds are singlebonds. A saturated hydrocarbon contains the maximum possiblenumber of hydrogen atoms for each carbon atom. Another namefor a saturated hydrocarbon is an alkane. Names of alkane com-pounds end in –ane, as in methane and propane.

Factors that determine the properties of a hydrocarbon arethe number of carbon atoms and how the atoms are arranged. Ahydrocarbon molecule can contain one carbon atom, as in methane,or thousands of carbon atoms, as in cellulose. The carbon atoms canbe arranged in a straight chain, a branched chain, or a ring.

Straight Chains Figure 4 lists the names, molecular formulas,structural formulas, and boiling points for four straight-chain alka-nes. Recall that a molecular formula shows the type and number ofatoms in a molecule of the compound. A structural formula showshow those atoms are arranged. The number of carbon atoms in astraight-chain alkane affects the state of the alkane at room tempera-ture. Methane and propane are gases. Pentane and octane are liquids.The more carbon atoms, the higher the boiling point is.

What is another name for a saturated hydrocarbon?

Figure 3 Microorganisms in thestomachs of a cow produce morethan 500 liters of methane (CH4)per day.

Name Methane PentanePropane Octane

MolecularFormula

C5H12CH4

H

H

H

C H

H

C CH

H

H

C

H

H H

C

H

H

C H

H

H

–42.1°C–161.5°C 36.0°C

H

H

C CH

H

H

C

H

H H

C

H

H

C

H

H

H

C

H

C

H

H

C

H

H

125.6°C

C CH

H

H

C

H

H

H

H

H

C8H18C3H8

BoilingPoint

StructuralFromula

Some Straight-Chain Alkanes

Figure 4 Molecules of ethane,propane, pentane, and octanehave two, three, five, and eightcarbon atoms, respectively.Making GeneralizationsHow does increasing thenumber of carbon atoms affectthe boiling point of a straight-chain alkane?

264 Chapter 9

SaturatedHydrocarbonsIntegrate Language ArtsTell students that one definition ofsaturated is “filled to capacity.” Sosaturated can mean “the inability tocontain, absorb, receive, or hold.” For example, the ground may besaturated with water after a heavyrainstorm, meaning it can absorb nomore water. Have students use thesemeanings to paraphrase the definition of the vocabulary term saturatedhydrocarbon. (Possible answer: In asaturated hydrocarbon, carbon atoms do not have the capacity to bond toadditional hydrogen atoms.)Verbal

Comparing Models of MoleculesPurpose Students compare ball-and-stick models and structural formulas for methane and propane.

Materials molecular model kit

Procedure Write the structuralformulas and chemical formulas formethane and propane on the board.Remind students that a structuralformula provides more information than a molecular formula because itshows how the atoms are arranged in a molecule. Then, show students ball-and-stick models for methane andpropane. Explain that a ball-and-stickmodel shows the angles between atomsin a molecule and the overall shape of the molecule. (Students may recallmethane’s tetrahedral shape from theQuick Lab in Section 6.3.) The bondangle between carbon and hydrogen is 109.5� in methane and propane.

Expected Outcome Students observethe similarities and differences betweenthe structures of methane and propane molecules.Visual, Logical

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Section 9.1 (continued)

Naming Hydrocarbons Names of straight-and branched-chain hydrocarbons use prefixesto indicate the number of carbon atoms in thelongest continuous chain. Except for meth- (1),eth- (2), and prop- (3), the prefixes used matchthose shown in Figure 20 on p. 175. Forbranched-chain hydrocarbons, the carbon

atoms in the longest continuous chain arenumbered beginning at one end of the chain.Prefixes that combine a numeral and a groupdesignation are used to show the type andlocation of branches. Using this system, theofficial name for isobutane (shown in Figure 5)is 2-methylpropane.

Facts and Figures

Comparing Isomers

Materials30 marshmallows, 70 raisins, 30 toothpicks

Procedure1. Use marshmallows to represent carbon atoms,

and raisins to represent hydrogen atoms, as inthe model of propane shown. CAUTION Donot eat anything in the laboratory. Break thetoothpicks in half to represent single bonds.Build models of five different isomers ofhexane (C6H14).

2. For each model, attach all six carbon atomsfirst. Then attach hydrogen atoms until eachcarbon atom has four bonds.

Analyze and Conclude1. Using Models Draw a structural formula for

each isomer.

2. Predicting Would pentane (C5H12) orheptane (C7H16) have more isomers thanhexane? Explain your answer.

Figure 5 Butane, isobutane, andcyclobutane represent three waysthat carbon atoms are arranged inan alkane—in a straight chain, ina branched chain, and in a ring. Classifying Explain why butaneand cyclobutane are not isomers.

Branched Chains Look at the butane and isobutane formulas inFigure 5. Both compounds have a molecular formula of C4H10, buttheir structural formulas are different. In isobutane, there is a branchat the point where a carbon atom bonds to three other carbon atoms.

Compounds with the same molecular formula but different struc-tural formulas are isomers. Differences in structure affect someproperties of isomers. Butane boils at –0.5°C, but isobutane boils at–11.7°C. The number of possible isomers increases rapidly each timean additional carbon atom is added to the chain. For example, octane(C8H18) has 18 isomers, while decane (C10H22) has 75.

Rings Figure 5 also shows the structural formula for cyclobutane.The carbon atoms in cyclobutane are linked in a four-carbon ring.Because each carbon atom forms bonds with two other carbon atoms,it can bond with only two hydrogen atoms. So cyclobutane (C4H8)molecules have two fewer hydrogen atoms than butane (C4H10) mol-ecules. Most ring alkanes, or cyclic hydrocarbons, have rings with fiveor six carbons.

Carbon Chemistry 265

H

C4H10

Butane

C CH

H

H

C

H

H H

C

H

H

H

C4H10

Isobutane

C CH

H

H

C

H H

H

H

H C

H

H

C4H8

Cyclobutane

CH

H

C

H

H

HH C

H H

C

Comparing Isomers

ObjectiveAfter completing this activity, studentswill be able to• use structural formulas and models to

describe the isomers of hexane.

Skills Focus Observing, Predicting,Using Models

Prep Time 10 minutes.

Materials 30 marshmallows, 70 raisins, 50 toothpicks

Advance Prep Set out raisins,marshmallows, and toothpicks in acentral location.

Class Time 15–20 minutes

Safety Remind students never to eatanything in the laboratory.

Teaching Tips• Display ball-and-stick models that are

initially oriented with the branches atopposite ends. Rotate one model 180�to show that the structural formulasrepresent the same isomer.

Expected Outcome Students shouldbe able to draw the structural formulasfor the isomers of hexane.

Analyze and Conclude1. There are five straight- and branched-chain isomers of hexane:(1) C C C C C C (hexane)

(2) C C C C C (3) C C C C C

C C(2-methylpropane) (3-methylpropane)

(4) C C C C (5) C

C C C C C C(2, 3-dimethylbutane)

C(2, 2-dimethylbutane)

2. Heptane. The greater the number ofcarbon atoms, the greater the possibilityfor different lengths and locations ofbranches along a central chain. Logical

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Carbon Chemistry 265

Hydrocarbons An isomer with branchesoften has a lower boiling point than itscorresponding straight-chain isomer becauseless efficient packing results in weaker inter-molecular forces. There is a strain on rings withonly three or four carbon atoms because of the bond angles between the carbon atoms.

In general, unsaturated hydrocarbons are morereactive than saturated hydrocarbons becauseatoms or groups of atoms can be added to themolecule at the locations of double and triplebonds. Combustion reactions are the exceptionto this trend.

Facts and Figures

Answer to . . .

Figure 4 The boiling point increases.

Figure 5 Cyclobutane and butane donot have the same formula.

Alkane

266 Chapter 9

Unsaturated HydrocarbonsA hydrocarbon that contains one or more double or triple bonds isan unsaturated hydrocarbon. These hydrocarbons are classified bybond type and the arrangement of their carbon atoms. Thereare three types of unsaturated hydrocarbons—alkenes, alkynes, andaromatic hydrocarbons.

Alkenes Many fruit-bearing plants produce ethene (C2H4), whichcontrols the rate at which fruits, such as the tomato in Figure 6A, ripen.There is a double bond between the two carbon atoms in ethene.Hydrocarbons that have one or more carbon-carbon double bonds arealkenes. The names of alkenes end in –ene. Plastics used in trash bagsand milk jugs are produced by reactions involving ethene.

Alkynes In 1895, Henry-Louis Le Châtelier reported thata flame produced when ethyne burned had a temperatureabout 1000°C higher than a flame produced when hydrogenburns. Ethyne (C2H2), also known as acetylene, is an alkyne.Alkynes are straight- or branched-chain hydrocarbons thathave one or more triple bonds. Alkyne names end in –yne.

Alkynes are the most reactive hydrocarbon compounds.The welder in Figure 6B is burning a mixture of oxygen andacetylene in an oxyacetylene torch. The temperature of theflame produced approaches 3500°C. At that temperature,most metals can be melted and welded together. The acety-lene and oxygen are stored under pressure in tanks.

Aromatic Hydrocarbons The Belgian stamp in Figure 6Chonors Friedrich Kekulé (1829–1896), who figured out that benzene(C6H6) is an unsaturated hydrocarbon with a ring structure. Althoughthe formula shows alternating single and double bonds, the six bonds inthe ring are identical. Six of the valence electrons are shared by all sixcarbon atoms. Hydrocarbons that contain similar ring structures areknown as aromatic hydrocarbons. The name was chosen because manyof these compounds have strong aromas or odors.

What is an unsaturated hydrocarbon?

EthyneC CH H

Ethene

C CH

H

H

H

Benzene

C

HC

CC

H

C CH H

H H

A

B

C

Figure 6 There are three types ofunsaturated hydrocarbons. A Ethene is an alkene that controlsthe ripening of a tomato. B Ethyne is an alkyne used intorches that cut metals or weldthem together. C Kekulé figuredout the ring structure of thearomatic hydrocarbon benzene.

266 Chapter 9

UnsaturatedHydrocarbonsIntegrate Social StudiesFriedrich August Kekulé claimed to have developed the model for the ringstructure of benzene after he had adream about a snake chasing its owntail. Have students find out more aboutthis German chemist’s work. Ask, Whatother major contribution did Kekulémake to organic chemistry? (In 1854,he was one of the first to theorize thatcarbon forms four bonds.)Verbal

Integrate HealthThe terms saturated and unsaturated arealso used to describe fats. The term fat iscommonly used to refer to the fats andoils that are obtained from animals andplants. (These fats are esters that formwhen fatty acids react with glycerol, analcohol with three �OH groups.) Thereare three long hydrocarbon chains ineach fat molecule. The chains contain aneven number of carbon atoms (typicallybetween 12 and 24). If the hydrocarbonchains contain only single bonds, thenthe fat is classified as a saturated fat. Ifthere are one or more double or triplebonds in the hydrocarbon chains, thenthe fat is classified as an unsaturated fat.Unsaturated fats, such as corn oil andolive oil, are generally liquids at roomtemperature. Saturated fats, such asbutter and bacon grease, tend to besolids at room temperature. A diet highin saturated fats has been linked to heartdisease. Have students examine foodlabels to determine which types of foodscontain saturated and unsaturated fats.You may also ask students to researchwhether cooking with unsaturated fats,such as olive oil, provides any healthbenefits other than preventing heart disease.Visual

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Section 9.1 (continued)

Carbon Chemistry 267

For: Links on fossil fuels

Visit: www.SciLinks.org

Web Code: ccn-1091

Figure 7 Fossil fuels form fromthe remains of plants andanimals. A The ferns shown aresimilar to ferns that lived millionsof years ago. B The imprints offerns left on the lump of coal areevidence that the coal formedwhen plant remains werecompressed under layers of rockand soil.

Fossil FuelsSome hydrocarbons were formed from plants and animals that lived inEarth’s oceans and swamps millions of years ago. After those plantsand animals died, they were buried under layers of rock and soil. Hightemperature and pressure deep in Earth’s crust changed those remainsinto deposits of hydrocarbons called fossil fuels. Fossil fuels are mix-tures of hydrocarbons that formed from the remains of plants oranimals. Three types of fossil fuels are coal, natural gas, andpetroleum. The type of fossil fuel produced depends on the origin ofthe organic material and the conditions under which it decays.

Coal The ferns in Figure 7A are similar to those that produced thecoal in Figure 7B. Coal is a solid fossil fuel that began to form about300 million years ago in ancient swamps. Giant tree ferns and otherplants were buried in those swamps. After millions of years of pres-sure, the plant remains produced a mixture of hydrocarbons. Most ofthe hydrocarbons in coal are aromatic hydrocarbons with high molarmasses. These compounds have a high ratio of carbon to hydrogen. Soburning coal produces more soot than burning other fossil fuels does.

Natural Gas The second main fossil fuel, natural gas, formed fromthe remains of marine organisms. The main component of natural gasis methane—the same compound produced by cows as they digest grass.Natural gas also contains ethane, propane, and isomers of butane.Natural gas is distributed through a network of underground pipes. It isused for heating and cooking, and to generate some electricity. Depositsof natural gas are found along with deposits of coal and petroleum.

Petroleum The third main fossil fuel, petroleum, also formed fromthe remains of marine organisms. Petroleum, often known as crude oil,is pumped from deep beneath Earth’s surface. It is a complex liquid mix-ture of hydrocarbons, mainly long-branched alkanes and alkenes. Forpetroleum to be useful, it must be separated into simpler mixtures, orfractions, such as gasoline and heating oil.

A

B

Fossil Fuels

Fractional Distillation

Purpose Students will observefractional distillation of a mixture of organic compounds.

Materials distillation apparatus withstand, 50 mL water, 50 mL ethanol, 60 mL mineral oil, hot plate, 60-mLbeakers (6), concave glass beaker covers (3), shield, dropper pipets (5)

Procedure Explain that fractionaldistillation is a method of separatingmixtures using differences in boilingpoints. Measure 50 mL of water and 50 mL of ethanol in two different beakersand mix them together in the distillationchamber. Heat the mixture, keeping thetemperature at about 85�C, just above theboiling point of ethanol and below theboiling point of water. Three times duringthe process, collect the distilled liquid(distillate) in a separate beaker, and coverthe beaker. After you complete thedistillation, place a drop of pure ethanoland a drop of pure water in a beaker ofmineral oil. Next, place a drop from eachbeaker of distilled liquid into the mineraloil. Have students notice whether thedrops float or how quickly they sink.

Safety Place a blast shield between theequipment and students. Use mitts ortongs to handle hot glass.

Expected Outcome The ethanol willcollect more rapidly in the catch beaker.Pure ethanol floats in mineral oil, andpure water sinks. Students can infer therelative concentrations of ethanol andwater in each distillate sample by thebehavior of the drops in the mineral oil.Visual

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Carbon Chemistry 267

Download a worksheet on fossilfuels for students to complete, andfind additional teacher supportfrom NSTA SciLinks.

Answer to . . .

A hydrocarbon thatcontains one or more

double or triple bonds

268 Chapter 9

Figure 8 The petroleum pumpedfrom underground deposits is acomplex mixture of hydrocarbons.A At a refinery, petroleum isseparated into mixtures calledfractions. B The diagram showssome of the fractions that can becollected from a distillation tower.The labels provide data on thecompounds within a fraction. Forexample, compounds in kerosenehave from 12 to 16 carbon atomsand condense at temperaturesbetween 200°C and 250°C.Interpreting Diagrams Howmany carbon atoms are there inthe compounds in the petroleumgas fraction?

Petroleum gas < 40°C C1 to C4

Crude oil

Crude oil vapors

Heating burner

Distillation Tower

Gasoline 40°–200°C C5 to C12

Kerosene, jet fuel 200°–250°C C12 to C16

Heating oil 250°–300°C C15 to C18

Lubricating oil 300°–370°C ≥ C19

Residue, asphalt ≥ C25

BA

The diagram in Figure 8B shows how petroleum is separated intofractions through a type of distillation called fractional distillation.When petroleum is heated in a distillation tower, most of the hydro-carbons vaporize. The vapors rise through the tower and condense asthe temperature decreases. Compounds with higher boiling points con-dense first. They are collected near the bottom of the tower.

Combustion of Fossil FuelsThe energy released from fossil fuels through combustion is used toheat buildings, cook food, or for transportation. Recall that energyfrom the combustion of propane heats the air in a hot-air balloon.

C3H8 � 5O2h 3CO2 + 4H2O (complete combustion)

The primary products of the complete combustion of fossil fuelsare carbon dioxide and water. Burning fossil fuels increases the amountof carbon dioxide in the atmosphere. This increase may affect tempera-tures, amounts of rain, and sea levels worldwide. Some sulfur andnitrogen are in fossil fuels, and air contains nitrogen. So nitrogen oxidesand sulfur dioxide are produced during the combustion of fossil fuels.

Incomplete Combustion In stoves and furnaces, there maynot be enough oxygen available for complete combustion of all the fuel.So a deadly gas, carbon monoxide, is produced. This colorless, odor-less gas can be inhaled and absorbed by blood. It keeps hemoglobinfrom carrying oxygen to cells. Safety experts recommend that homesheated with natural gas or heating oil have carbon monoxide detectors.

2C3H8 � 7O2h 6CO + 8H2O (incomplete combustion)

When fossil fuels undergo incomplete combustion in factories or powerplants, they also produce tiny particles of carbon. Inhaling these parti-cles can cause heart and lung problems.

268 Chapter 9

Build Science SkillsProblem Solving Tell students thatthey are given an unknown alkane. Have them use Figure 8 to answer thefollowing question. Ask, How could you determine if the alkane is one ofthe components of gasoline? (If itsboiling point is between 40�C and 100�C,then the alkane may be a component of gasoline.)Visual, Logical

FYIIn industry documents that describefractional distillation, there is variation in the names of the fractions collected,the length of the carbon chains in a fraction, and the temperature range at which a fraction is collected. There is agreement on how the processseparates the numerous substances in petroleum into fractions.

Combustion of Fossil FuelsBuild Math SkillsBalancing Equations Remindstudents that only the coefficients infront of the formulas, and not thesubscripts in the formulas, may bechanged when they balance anequation. Have students practicebalancing the equation for the complete combustion of ethane:

C2H6 + O2 h CO2 + H2O

(2C2H6 + 7O2 h 4CO2 + 6H2O)

Then, have students determine thebalanced equation for incompletecombustion of ethane.

(2C2H6 + 5O2 h 4CO + 6H2O)Logical

Direct students to the Math Skills inthe Skills and Reference Handbookat the end of the student text foradditional help.

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Section 9.1 (continued)

Octane Number Octane ratings are used to compare blends of gasoline. Twosubstances found in gasoline are used asreference fuels: n-heptane and isooctane(2,2,4-trimethylpentane). Because n-heptaneself-ignites when compressed, it burns toorapidly, causing a knocking sound in a poorlyperforming engine. Isooctane will not self-

ignite if it is compressed before sparking. The octane rating describes a blend as thoughit contained only n-heptane and isooctane.With an octane rating of 89, gasoline performsas if it contained 89% isooctane and 11% n-heptane. With a higher octane rating, thepossibility of knocking is lower.

Facts and Figures

Section 9.1 Assessment

Reviewing Concepts1. Name three forms of carbon.

2. What two factors can affect the propertiesof a hydrocarbon?

3. Name the three categories of unsaturatedhydrocarbons.

4. Name the three main fossil fuels.

5. What are the two primary products of thecomplete combustion of fossil fuels?

6. What are three ways that carbon atoms can bearranged in hydrocarbon molecules?

Critical Thinking7. Classifying Why isn’t carbon dioxide

considered an organic compound?

8. Applying Concepts Draw structuralformulas for the two branched-chain isomersof pentane, C5H12.

Saturation Compare the way saturatedand unsaturated are used in describinghydrocarbons to how they were used indescribing solutions in Section 8.2.

Carbon Chemistry 269

Figure 9 This statue of GeorgeWashington was sculpted frommarble in 1918. The photographwas taken in the 1990s. Thedamage was done by calciumcarbonate in the marble reactingwith sulfuric acid in acid rain.

Acid Rain The combustion of fossil fuels causes the acidity of rainto increase. Rain is always slightly acidic, with a pH of about 5.6,because carbon dioxide dissolves in water droplets and forms carbonicacid, H2CO3. Sulfur dioxide and nitrogen oxides released into theatmosphere also dissolve in water, forming sulfuric acid, H2SO4, andnitric acid, HNO3. The pH of rain containing sulfuric acid and nitricacid can be as low as 2.7. These acids damage stone structures like thestatue in Figure 9. They also damage metal and concrete.

Build Math SkillsInterpreting Equations Write theequations for the complete andincomplete combustion of propane onthe board. Ask, Why are there 5 molesof oxygen in the equation for thecomplete combustion, but 7 moles of oxygen in the equation for theincomplete combustion? Let studentsfigure out that the number of moles ofmethane is not the same in the twoequations. Then, multiply the coefficientsin the first equation by 2 to show that theamount of oxygen used is greater. Logical

Direct students to the Math Skills inthe Skills and Reference Handbookat the end of the student text foradditional help.

ASSESSEvaluateUnderstandingHave students make flashcards for thekey concepts and vocabulary in thissection. For example, for each type of unsaturated hydrocarbon, they canmake a card that has an example and a definition. Students can use theflashcards to quiz one another.

ReteachUse the structural formulas in the texton pp. 265 and 266 to review each typeof hydrocarbon.

In a saturated solution, the solventcontains the maximum amount of soluteat a given temperature. A saturatedhydrocarbon contains the maximumnumber of hydrogen atoms for eachcarbon atom. More solute can be addedto an unsaturated solution. Morehydrogen atoms can be added to anunsaturated hydrocarbon.

If your class subscribesto iText, use it to review key concepts in Section 9.1.

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Carbon Chemistry 269

5. Carbon dioxide and water6. As a straight chain, a branched chain, or a ring7. Carbon dioxide does not contain anyhydrogen atoms.8. C C C C C

C C C C(2-methylbutane)

C(2, 2-dimethylpropane)

Section 9.1 Assessment

1. Diamond, graphite, and fullerenes are formsof carbon.2. Factors that determine the properties of a hydrocarbon are the number of carbonatoms and how the atoms are arranged.3. The three types of unsaturated hydro-carbons are alkenes, alkynes, and aromatichydrocarbons.4. Three types of fossil fuels are coal, naturalgas, and petroleum.

Answer to . . .

Figure 8 Molecules of compounds in petroleum gas contain one to fourcarbon atoms.

Breathing EasyCoal-burning power stations produce more than halfthe electricity used in the United States. An averagecoal-burning power station emits about 10,000 tonsof sulfur dioxide and the same amount of nitrogenoxides each year.

Air in

FURNACE 2

Morelimestoneadded

Hot airjets

Unburnedfuel fromfurnace 1

FURNACE 1Cyclone separator

Hot gases out

Air in

Coal

Cycloneseparator

■1 Washing coalThe coal is crushedand washed toremove sulfur fromits surface. When thecoal is placed in awater-filled tank, thecoal floats to thesurface while thesulfur impurities sinkto the bottom.

■2 Furnace 1 A mixture of coal andlimestone floats on a stream of hot airin the furnace. Calcium carbonate in thelimestone reacts with sulfur dioxide toform calcium sulfate. The amount of airis limited and the temperature is heldlow to keep nitrogen from reactingwith oxygen.

■4 Furnace 2 Unburned coal fromthe first furnace is transferred intofurnace 2 for further burning. Morelimestone is added to react with anysulfur dioxide produced.

■3 Cycloneseparator Thecyclone separatesthe unburned fuelfrom the hot gases.

Coal andlimestone

270 Chapter 9

Oxides of sulfer and nitrogen cause smog and acid rain. Theyalso can irritate your lungs. The United States has a Clean CoalTechnology Program that encourages the development oftechnologies for reducing emissions of these harmful gases. Thediagram shows steps in the process for reducing these emissions.The process begins when sulfur is washed from the surface ofcoal and ends when cleaner air is released into the atmosphere.

270 Chapter 9

Breathing EasyBackgroundThe Department of Energy began The Clean Coal Technology Program inresponse to concerns about acid rain. Thediagram illustrates some of the methodsused to reduce emissions of nitrogenoxides and sulfur dioxide. (1) Sulfur that is not bonded to carbon is removed whencoal is crushed and washed. (2) Jets of air keep limestone and crushed coalsuspended so that the limestone can react with the sulfur dioxide. Because the temperature in the furnace is low andthe amount of air is limited, most of theoxygen reacts with fuel, not nitrogen. (7) Smokestacks may contain electrostaticprecipitators and scrubbers. As particles of ash pass through the precipitator, theygain a charge. They can be collected on a plate with an opposite charge. In onetype of scrubber, limewater is sprayed intothe stream of waste gases. The calciumhydroxide reacts with sulfur dioxide andforms solid calcium sulfate.

Build Science SkillsObserving

Purpose In this activity, students will use physical properties to separate a mixture of coal and sulfur.

Materials 100-mL beaker containing a 1:1 mixture of sulfur powder and coal dust, 100-mL graduated cylinder,stirring rod, distilled water, plastic pipet,100-mL beaker

Class Time 10–15 minutes

Procedure Provide each group with a beaker containing 10 g of the sulfur-coal mixture. Have them add 30 mL ofwater to the beaker and mix using astirring rod. Allow layers to form in themixture. Next have students use a pipetto transfer the layer of water containingcoal dust to a second beaker. Stir themixture and allow layers to form again.Have students compare their activity to the process described in Step 1 of the diagram.

Safety Students should wear safetygoggles and aprons.

L2

L2

Catalytic Converters The combustion ofpetroleum products in internal combustionengines produces emissions that contribute to air pollution. In a vehicle’s exhaust system,there is a catalytic converter. This devicecontains a mixture of catalysts for the oxi-dation of carbon monoxide and unburned

hydrocarbons to carbon dioxide and waterand the reduction of nitrogen oxides tonitrogen. The catalysts may be transitionmetals, such as platinum palladium, andrhodium; or oxides of transition metals, such as CuO and Cr2O3.

Facts and Figures

� Research the process of coal gasification. Writea paragraph describing one of the methodsused to convert coal into flammable gases.What gases are produced?What are the benefits ofcoal gasification? Are thereany problems withthe technology?

� Take a Discovery Channel VideoField Trip by watching“Clean Energy.”

Going Further

Gas turbine

Electricgenerator

Steamturbine

Condenser

Particlefilters

Heatexchanger

Chimney

Steamout

Boiler

Water in

■6 Particle filterHot gases from the furnacesare fed through filtersmade of tightly wovenfabric. The filters trap tinyparticles of coal and ashand prevent them fromentering the gas turbine.

■7 Heat exchanger Wastegases are cooled in theheat exchanger by a coilcontaining cold water. Thecooled and cleaned gases,containing dramaticallyreduced amounts of sulfurdioxide and nitrogenoxides, are emitted fromthe chimney.

■5 Boiler Water from thecondenser flows through pipesin the boiler. Hot gases fromfurnace 2 are fed into theboiler to heat the water. Thesteam created is used to spin asteam turbine. The exhaustgases are recycled back tofurnace 2. Video Field Trip

Carbon Chemistry 271

Expected Outcome Most of the sulfurwill settle to the bottom of the first beakerwhile the coal dust floats. Any remainingsulfur will settle to the bottom of thesecond beaker. This activity demonstrateswhat happens when coal is crushed andwashed prior to burning.Visual, Kinesthetic

Going FurtherThe United States Department of Energy has funded research into coalgasification. They are encouraging thedevelopment of methods for convertingsolid coal into gases that can be used to generate power. During gasification,coal reacts with steam and oxygen at a high temperature and pressure. Themethods produce a mixture of gases.Hydrogen and carbon monoxide aretypical products. The hydrogen can be separated from the raw mixture and used directly as fuel or it can becombined with carbon monoxide toproduce methane. Any carbon dioxideproduced is captured for commercialapplications or sequestered to prevent its release into the atmosphere.

If students search the Internet, theywill find descriptions of multiple methodsfor coal gasification, and information on the advantages and drawbacks of the methods. The main advantages ofcoal gasification are a reduction in airpollution and an increase in efficiency(more energy produced from the sameamount of coal). For now, drawbacksinclude the cost of equipment and ahigher cost per kilowatt for powergeneration. Other drawbacks are theamount of water required and theamount of wastewater produced. Verbal, Portfolio

L3

Carbon Chemistry 271

After students have viewed the Video Field Trip, askthem the following questions: What substancesdoes a fuel cell use to produce energy? Whatform of energy is produced? (The fuel cell usesoxygen [from air] and hydrogen. The fuel cellproduces electrical energy.) What technologicaladvance made fuel cells more efficient? (Thedevelopment of a new kind of membrane to separatethe oxygen and hydrogen) Give one advantage

that a fuel cell has over an internal combustionengine. (Student answers may include having nomoving parts, producing only water as a product, and being quieter.) What advantage does a vehi-cle that uses a fuel cell have over a vehicle thatuses batteries? (As long as fuel is provided, the fuelcell will continue to work.) If fuel cells are moreefficient (that is, if they have a higher ratio ofoutput energy to input energy) than internalcombustion engines, why do most cars still have internal combustion engines? (Because ofthe large investment already made in internal engine technology)

Video Field Trip

Clean Energy