Topic Fossil Fuels and Carbon Compounds

Fossil Fuels and Carbon Compounds

Unit 25 Fossil fuels

Unit 26 Homologous series, structural formulae and naming of carbon compounds

Unit 27 Alkanes and alkenes

Unit 28 Addition polymers

Topic 7

KeyC o ncepts

Fossil Fuels andCarbon Compounds

Fossil fuels• Origins anduses• Fractional distillationofpetroleum

andproperties of fractions• Consequences ofusing fossil fuels

Homologous series, structural formulae and naming of

carbon compounds• Unique natureof carbon• Structural formula, condensed

structural formula and skeletal formula• Homologous series and systematic

namingof alkanes, alkenes, alkanolsand alkanoic acids

Addition polymers• Monomers, polymers and repeating

units• Structures, properties anduses• Economic importanceofplastics• Environmental issues associatedwith

theuseofplastics

Alkanes and alkenes• Risks andbenefits ofusing fossil fuels• Cracking of fractionsofpetroleum• Important reactionsof alkanes and

alkenes

Topic 7� Fossil Fuels and Carbon Compounds

25.1 Fossil fuels—amajor energy source

25.2 Importance ofpetroleum

25.3 What is petroleumcomposedof?

25.4 Fractional distillationofpetroleum

25.5 Uses of fractionsofpetroleum

25.6 Demand for various fractionsofpetroleum

25.7 Combustion ofhydrocarbons

25.8 Carbon dioxide and the greenhouse effect

25.9 Majorairpollutantsfromcars,factories,incineratorsandpowerstations

25.10 Measures for reducing emissionof air pollutants

25.11 Impact of using fossil fuels on our quality of life and theenvironment

Unit 25 Fossil fuels

�Unit 25 Fossil fuels

25.1 – 25.6

Summary

1 Themajor fossil fuels are coal, petroleumandnatural gas.

2 Fossil fuelswereformedfromtheremainsofplantsandanimalsthat livedmillionsof years ago.

3 Petroleum is a mixture mainly composed of hydrocarbons. Hydrocarbons arecompounds that containonly atomsof carbonandhydrogen.

hydrocarbons found in petroleum

cycloalkanesaromatic

hydrocarbonsalkanes

4 Fractionaldistillationseparatespetroleumintofractionswithdifferentboilingpointranges.

Fraction Boiling point range (°C)

Number of carbon atoms per molecule General Properties

Refinery gases below40 1 – 4fractions containinghydrocarbonswith a smallernumberof carbonatoms in theirmolecules:

•lighter in colour

•less viscous

•easier to evaporate

•more flammable

•burn with a clearer flame

Petrol,naphtha 40 – 170 5 – 10

Kerosene 170 – 250 10 – 14

Diesel oil 250 – 350 14 – 25fractions containinghydrocarbonswith a greaternumberof carbonatoms in theirmolecules:

•darker in colour

•more viscous

•more difficult to evaporate

•less flammable

•burn with a sootier flame

Fuel oil,lubricatingoil

andwaxover 350 above25

5 Themainusesof refinedpetroleumare:

a) as fuels for transportation;

b)as fuels for generating electricity;

c) as fuels forheating; and

d)as rawmaterials in thepetrochemical industry.

ExamtipsExamtipsExamtipsExamtips ♦ DoNOTuse the terms ‘petroleum’ and ‘petrol’ interchangeably.

♦ Fractional distillation involves a physical change. Ethene is NOTmanufactureddirectly by fractional distillationof petroleum.


Example

Petroleum can be separated into different products such as petrol, diesel oil and fueloil by a certainprocess.

a) Name theprocess. (1mark)

b)Explainwhetherpetrol ordiesel oilhas ahigher viscosity. (2marks)

c) Explainwhetherpetrol ordiesel oil is a cleaner fuel. (2marks)

Answer

a) Fractionaldistillation (1)

b)Diesel oilhas ahigher viscosity. (1)

ThevanderWaals’forcesbetweenthemoleculesindieseloilarestrongerthanthoseinpetrol. (1)

c) Petrol is a cleaner fuel. (1)

Petrol burnsmore completely /has a lower carbon content thandiesel oil. (1)

25.7 – 25.11

Summary

1 Combustionofhydrocarbons is an exothermic reaction.

2 Burningof fossil fuelsproducescarbondioxideandwatervapour,whichcontributeto the greenhouse effect.

3 Major air pollutants fromusing fossil fuels include:

a) carbonmonoxide;

b)unburnthydrocarbons / volatile organic compounds;

➤Viscosity has beendiscussed in Topic 6Microscopic World II.

The viscosity of a liquid is ameasure of a liquid’s resistance to flow.

The viscosity of a liquid depends on:

– the strength of attractive forces betweenmolecules; and

– the tendency ofmolecules to becomeentangled with eachother.

A liquid with strong intermolecular forces has a higher viscosity than onewithweak intermolecular forces.

Ifthemoleculesofaliquidareintheformoflongchains,theycanbecomeentangled and the viscosity of the liquid will be high.

➤Questions oftengive two fuels and askwhich is a cleaner fuel.

e.g.

Comparing liquefiedpetroleum gas (LPG) anddiesel oil.

RemarksRemarks*

�Unit 25 Fossil fuels

c) suspendedparticulates;

d)oxidesofnitrogen;

e) sulphurdioxide.

4 The table below summarizes possible measures for reducing the emission of airpollutants from the combustionof fossil fuels.

Pollutant Measures for reducing the emission of the pollutant

Oxidesofnitrogen

•installing catalytic converters in exhaust systemsofmotor vehicles

•installing lownitrogenoxideburners inpower stations

Sulphurdioxide

•using low-sulphur coal insteadofhigh-sulphur coal

•installing flue gasdesulphurization systemsor scrubbers inpower stations

Particulates•using electrostaticprecipitators inpower stations

•installing particulate removaldevices inmotor vehicles

ExamtipsExamtipsExamtipsExamtips ♦ Although carbon dioxide is a greenhouse gas, it is NOT considered asan air pollutant.

♦ Water vapour is a greenhousegas.

♦ Carbondioxide doesNOT cause acid rain.

♦ Questions often ask about the current air pollution problems inHong Kong and possible measures for reducing the emission of airpollutants.

e.g.

– using natural gas to replace coal in generating electricity;

– using electricity to replacepetrol to drive cars.

♦ Questions often ask about acid rain.

– acid rain refers to rain with pH less than5.6;

– air pollutants that lead to acid rain (NOx and SO2);

– what environmental problems are causedby acid rain.

♦ Students should be able to match the device with the air pollutant(s)it can reduce.

♦ Gasohol is amixture of ethanol andpetrol.

– Advantages of using gasohol over ethanol:

✧gasohol is less flammable;

✧more energy canbeobtained fromgasohol.

– Advantages of using gasohol over petrol:

✧gasohol undergoes complete combustionmore readily;

✧gasohol gives less carbon monoxide / particulates / soot / smokeupon combustion.


Example

The exhaust gasofmotor vehicles contains carbonmonoxide,oxidesofnitrogenandparticulates.

a) i) Explainwhy the exhaust gas containsoxidesofnitrogen. (1mark)

ii)State ONE environmental problem associated with the emission of oxides ofnitrogen into the atmosphere. (1mark)

b)StateONEhealthhazard associatedwithparticulates. (1mark)

c) Suggest adevice that canbe installed inamotorvehicle to reduce the emissionofcarbonmonoxideandoxidesofnitrogen.Describethereactionsinvolvedandwriterelevant chemical equations. (3marks)

Answer

a) i) Insidetheenginesofmotorvehicles,theairgetssohotthatnitrogenandoxygenreact together, formingoxidesofnitrogen. (1)

ii)Formation of acid rain / formation of photochemical smog with unburnthydrocarbons. (1)

b)Irritate respiratory system (1)

c) Catalytic converter (1)

Oxidesofnitrogen reactwith carbonmonoxide as theypass through the catalyst.Nitrogen and carbondioxide are formed. (1)

2CO(g) + 2NO(g)catalyst

N2(g) + 2CO2(g)

The excess carbonmonoxide is oxidizedby air to carbondioxide. (1)

2CO(g) +O2(g)catalyst

2CO2(g)

➤Questions often ask how carbon monoxide and oxides of nitrogen areformed insidemotor vehicle engines.

➤Amongallthedevicesforreducingairpollution,questionsaskaboutreactionsoccurring in a catalytic convertermost often.

➤Be carefulwith the spelling of the term ‘catalytic converter’.

➤The following measures can help reduce the level of carbon monoxide atthe road side:

– using liquefiedpetroleum gas a fuel formotor vehicles;

– installing catalytic converter inmotor vehicles.

➤Catalyticconvertersincreasetheemissionofcarbondioxide.Thus,installingthemdoNOThelp reduceglobal warming.

➤A catalytic converter is NOTused to remove sulphur dioxide.

RemarksRemarks*

�Unit 26 Homologous series, structural formulae and naming of carbon compounds

26.1 A look atmolecules of compounds inpetroleum

26.2 Chemistry of carbon compounds

26.3 Representing molecular structuresof carbon compounds

26.4 Molecular models

26.5 Functional groups

26.6 Homologous series

26.7 The alkanes

26.8 Naming straight-chain andbranched-chain alkanes

26.9 Naming alkenes

26.10 Naming alkanols

26.11 Naming alkanoic acids

26.12 Physical properties of alkanes

Homologous series, structural formulae and naming of carbon compoundsUnit 26

Topic 710 Fossil Fuels and Carbon Compounds

26.1 – 26.12

Summary

1 Carboncompoundscanberepresentedbystructural formulae,condensedstructuralformulae and skeletal formulae.

Structural formula Condensed structural formula Skeletal formula

HH

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C CH3(CH2)3CH3

2 A functionalgroup isanatom,oragroupofatoms,whichdeterminesmostof theproperties of a compound.

3 Afamilyofcompoundscontainingthesamefunctionalgroupiscalledahomologousseries.

Members in ahomologous series show the following characteristics:

a) have the samegeneral formula;

b)eachmemberdiffers from thenextby a –CH2–unit;

c) showa gradual change inphysical properties; and

d)show similar chemicalproperties.

4 Alkaneshave the general formulaCnH2n+2.

Name Molecular formula Condensed structural formula

Methane CH4 CH4

Ethane C2H6 CH3CH3

Propane C3H8 CH3CH2CH3

Butane C4H10 CH3CH2CH2CH3

Pentane C5H12 CH3CH2CH2CH2CH3

Hexane C6H14 CH3CH2CH2CH2CH2CH3

Heptane C7H16 CH3CH2CH2CH2CH2CH2CH3

Octane C8H18 CH3CH2CH2CH2CH2CH2CH2CH3

The IUPACname for a branched-chain alkane consists of twoparts:

Prefixes

identify the alkyl groups and give their locations

Parent

describes the maincarbon chain

11Unit 26 Homologous series, structural formulae and naming of carbon compounds

5 Some commonhomologous series and functional groups

Homologous series

General formula

Functional group Naming Example(s)

Alkenes CnH2n C C

name the compoundswith the rules as if foralkanes, but using thesuffix –ene instead of–ane

CH3CH2CH=CH2

but-1-ene

CH3CH=CHCH3

but-2-ene

Alkanols CnH2n+1OH O H

name the compound byreplacing the last letter‘e’ of the correspondingalkaneby the suffix –ol

CH3CH2CH2CH2OHbutan-1-ol

CH3CH2CH(OH)CH3

butan-2-ol

Alkanoicacids CnH2n+1COOH

O

O HC

name the compound byreplacing the last letter‘e’ of the correspondingalkane by the suffix –oicacid; the carbon atomof the carboxyl group isassignednumber1.

CH3CH2CH2COOHbutanoic acid

6 a) The melting points and boiling points of alkanes rise as the number of carbonatoms in the alkanemolecules increases.

Name Molecular formula

Melting point (°C)

Boiling point (°C)

State at room temperature and pressure

Methane

Ethane

Propane

Butane

CH4

C2H6

C3H8

C4H10

–182

–183

–190

–138

–162

–89

–42

–0.5

gas

Pentane

Hexane

C5H12

C6H14

–130

–95

36

69liquid

Number of carbon atoms in the alkane molecule

Boi

lin

g p

oin

t of

al

kan

e (°

C)

b)Alkanes are insoluble inwater.


ExamtipsExamtipsExamtipsExamtips ♦ Studentsshouldbeabletodistinguishbetweenthe‘structuralformula’and the ‘molecular formula’ of a compound.

♦ Students should be able to recognize the number of carbon atoms intheparent chainofa compound.ThecarbonatomsmayNOTbe inastraight line.

e.g.

1C 2C 3C

4C

Br

H

H

H

H

H

H

H

The IUPACnameof the above compound is 3-bromobut-1-ene.

4CH3

1CH3

3C 2C OHH

H

H

The IUPACnameof the above compound is butan-2-ol.

3,4C2H5

H3C2C 1CH3

OH

The IUPACnameof the above compound is 2-methylbutan-2-ol.

♦ When drawing the structures of different compounds with the samemolecular formula,doNOT represent the samecompound indifferentways.

e.g.

are two differentways of representing hexane.

are two differentways of representing 2-methylpentane.

CH3

H C

H

C

H

H

C

H

C

H

H

C

H

H H H

C

H

H

H H C

H

C

H

H

C

H

C

H

H

C

H

H H

Hand

CH3CH3

H C

H

C

H

C

H

C

H

H

C

H

H H H

H H C

H

C

H

H

C

H

C

H

C

H

H H H

Hand

13Unit 26 Homologous series, structural formulae and naming of carbon compounds

Example

Both pentane (C5H12) and octane (C8H18) are members of the same homologousseries.

a) Name thehomologous series towhichpentane andoctanebelong. (1mark)

b)Using pentane and octane as examples, illustrate TWO characteristics of membersof ahomologous series. (2marks)

Answer

a) Alkanes (1)

b)Any twoof the following:

• Members in a homologous series have the same general formula. The generalformula forpentane andoctane isCnH2n+2. (1)

• Members in a homologous series show a gradual change in physical properties.The boiling point / melting point / viscosity of octane is higher than that ofpentane. (1)

• Members inahomologousseriesshowsimilarchemicalproperties.Bothpentaneandoctaneundergo substitution reactionwithbromine / chlorine. (1)

➤Members in the same homologous series have the same general formula,NOT the samemolecular formula. ✔

✘

➤The relative molecular mass of each successive member differs by 14 (i.e.relative atomic mass ofC+2 x relative atomicmass ofH).

RemarksRemarks*


27.1 Risks and benefits of using fossil fuels to the society andenvironment

27.2 Saturated andunsaturatedhydrocarbons

27.3 Important reactionsof alkanes

27.4 Meeting the demand for the petrol fraction from fractionaldistillationofpetroleum

27.5 Cracking of fractionsofpetroleum

27.6 Importance of cracking

27.7 Alkenes

27.8 Physical properties of alkenes

27.9 Important reactionsof alkenes

27.10 Wind power—Analternative sourceof energy

Unit 27 Alkanes and alkenes

1�Unit 27 Alkanes and alkenes

27.1 – 27.6

Summary

1 Hydrocarbons canbe classified as saturated andunsaturated.

saturated

containing only C–C bond(s)

hydrocarbons

unsaturated

containing C=C or C C bond(s)

2 The following table summarizes important reactionsof alkanes.

Reaction Examples

1 Combustion — in a good supply ofoxygen, alkanes burn completely toformcarbondioxide andwater

Complete combustion:

C5H12(g) + 8O2(g) 5CO2(g) + 6H2O(l)

Incomplete combustion:

C5H12(g) +11

2O2(g) 5CO(g) + 6H2O(l)

C5H12(g) + 3O2(g) 5C(s) + 6H2O(l)

2 Substitution reaction with halogens— formationofhaloalkanes

CH4(g) +Cl2(g) CH3Cl(g) +HCl(g)

CH3Cl(g) +Cl2(g) CH2Cl2(l) +HCl(g)

CH2Cl2(l) +Cl2(g) CHCl3(l) +HCl(g)

CHCl3(l) +Cl2(g) CCl4(l) +HCl(g)

ExamtipsExamtipsExamtipsExamtips ♦ Questions often ask students to decide which of the two givencompounds will burn with amore sooty flame.

e.g.

Which compound, pentane (C5H12) or octane (C8H18), will burn with amore sooty flame? Explain.

Octane will burn with amore sooty flame.

Octane has a higher percentage of carbon by mass. Its possibility ofundergoing incomplete combustion to give carbon is higher.


Example

Anon-luminousflameisobtainedwhentheairholeofaBunsenburnerisfullyopen.Methane is oneof the componentsof the gaseous fuelused in theBunsenburner.

With reference tomethane, explainwhy the flameobtained isnon-luminous. (2marks)

Answer

Enoughoxygen is providedwhen the airhole is fullyopen. (1)

Methaneundergoes complete combustion to give carbondioxide andwater. (1)

➤Whenusing aBunsenburnerwith the air hole closed, the fuel undergoesincomplete combustion. A luminous flame is obtained.

RemarksRemarks*

Example

Under suitable conditions,C2H6 reactswithBr2 to giveC2H5Br.

a) State the conditions required for the reaction. (2marks)

b)StateONEobservable change for the reaction. (1mark)

c) Outline themechanistic steps involved. (4marks)

Answer

a) Expose amixtureof ethane andbrominevapourunder sunlight / ultraviolet light. (1)

Use amixtureofC2H6 andBr2 in amole ratioof 1:1. (1)

b)Thebrowncolourof thebrominevapour fades. (1)

c) Initiation

(1)BrBr 2 Br

Propagation

(1)

H

H H

H H

C C H + Br

H+ BrH

H H

H H

C C


BrBrH

H H

H H

C C +

H

H H

H H

C C + BrBr

(1)

Termination

Anyoneof the following:

(1)BrBr+ BrBr

+ BrH

H H

H H

C C H

H H

H H

C C Br

(1)

H

H H

H H

C C +

H H

H H

C C H

H

H H

H H

C C H

H H

H H

C C

(1)

➤This substitution reactionof alkanewill NOToccur in thedark.

➤This substitution reaction is a redox reaction.

C2H6+Br2 C2H5Br+HBr

The oxidation number of Br decreases from0 to –1.

➤Studentsshouldbeabletospellcorrectlynamesofthestepsinvolvedinafreeradical substitution mechanism: initiation, propagation and termination.

➤This reaction isNOTaneffectivewayofpreparingbromoethanebecause itgives amixture of products (e.g.CH3CHBr2,CH3CBr3, etc.)

RemarksRemarks*


27.7 – 27.10

Summary

1 a) The melting and boiling points of alkenes are very close to those of thecorresponding alkanes.

Name Condensed structural formula

Melting point (°C)

Boiling point (°C)

State at room temperature and pressure

Ethene CH2=CH2 –169 –104

gasPropene CH3CH=CH2 –185 –47

But-1-ene CH3CH2CH=CH2 –185 –6

Pent-1-ene CH3(CH2)2CH=CH2 –138 30liquid

Hex-1-ene CH3(CH2)3CH=CH2 –140 63

b)Alkenes are insoluble inwater.

2 Alkenes areunsaturatedhydrocarbons. Theyundergo addition reactions.

C + XC CY C

X Y

3 The following table summarizes two addition reactions of alkenes. These reactionscanbeused as tests forunsaturated compounds.

Reaction Examples

Withbrominedissolved in anorganic solvent— theorangesolutionofbrominebecomescolourless rapidlywhen shakenwithan alkene

(g) + Br2 (in organic solvent)H

HH

HC C

H H (in organic solvent)

H

Br

C

H

Br

C

With cold acidifieddilutepotassiumpermanganatesolution— thepurple solutionofpotassiumpermanganatebecomes colourlessrapidlywhenshakenwith analkene

H

HH

HC C [O](g) + H2O(l)+ H H(aq)

H

O

C

H

O

H H

C

4 The followingdiagram summarizes some important information about cracking.

Cracking

The breaking down of larger hydrocarbon molecules with heat or catalyst to produce smaller hydrocarbon molecules.

Importance of cracking

• Producing extra petrol to meet demands

• As a source of alkenes to make a great variety of chemicals


Examples:

C14H30(l) C7H16(l) + C3H6(g) + 2C2H4(g)

tetradecane heptane propene ethene (a componentofpetrol)

C14H30(l) C12H26(l) + C2H4(g)

tetradecane dodecane ethene

ExamtipsExamtipsExamtipsExamtips ♦ Cracking is a chemical change.

It is an endothermic reaction.

It results in an increaseof number ofmolecules.

♦ Questions may ask students to compare cracking and fractionaldistillation.

– Both involve heating.

– Crackingisachemicalchangewhilefractionaldistillationisaphysicalchange.

♦ Questions often ask about the laboratory set-up for cracking.

DoNOTconfusethislaboratoryset-upwiththatforfractionaldistillationor reflux.

unglazed porcelainpieces (as a catalyst)

mineral wool soaked withmedicinalparaffin

heatclamp

gaseousproduct

water

♦ The reaction between an alkene and bromine / cold acidified dilutepotassium permanganate solution is an ‘addition reaction’, NOT‘additional reaction’. ✔

✘

♦ For the reaction between acidified dilute potassium permanganatesolution and excess propene,

– theoxidation number ofmanganese changes from+7 to+2;

– the acidified potassium permanganate solution is decolorized;

– the structure of theorganic product isCH3CH(OH)CH2OH.

♦ AC=Cbondcanonlyreactwithastrongeroxidizingagent,e.g.acidifiedpotassiumpermanganatesolution,butNOTwithaweakeronesuchasacidified potassium dichromate solution.


Example

Consider the following set-upof an experiment.

unglazed porcelain

glass wool with kerosene heat

tube A

tube B

blue litmus solution

tube C

acidified KMnO4(aq)

a) What is the chemicalprocess thatoccurs in the experiment. (1mark)

b)What is the functionof theunglazedporcelain? (1mark)

c) Will there be a colour change in each of the following solutions? Explain youranswer.

i) Solution in tubeB (2marks)

ii)Solution in tubeC (2marks)

Answer

a) Cracking (1)

b)As a catalyst (1)

c) i) There isno colour change in the solution (1)

becauseno acidic gas is formed in theprocess. (1)

ii)There is a colour change in the solution / the solution changes from purple tocolourless (1)

because alkenes are formed in theprocess. (1)

♦ Questions often ask about chemical tests for distinguishing betweenan alkane (a saturated hydrocarbon) and an alkene (an unsaturatedhydrocarbon). Do NOT just state a chemical test; mention the colourchange in each case,NOT just the final colour.

♦ Alkenes give negative results towards acidified dilute potassiumdichromate solution. Therefore the reagent CANNOT be used todistinguish an alkene froman alkane.

TestObservation

Alkane Alkene

Bromine (inorganic solvent)

the solution changes fromorange to colourless slowlyunder light

the solution changes fromorange to colourless rapidlyin thedark

AcidifieddiluteKMnO4(aq)

noobservable changethe solution changes frompurple to colourless

21Unit 27 Alkanes and alkenes

➤Questions often ask students to deduce molecular formulae of crackingproducts orwrite a chemical equation for the reaction.

Notice that thenumberof carbon / hydrogenatomson the left-hand sideand the right-hand side of the equation are equal.

e.g.

C12H26 2C2H4+C8H18

Number ofC atoms on left-hand side =12 =2 x 2+8 =number ofC atoms on right-hand side

Number ofH atoms on left-hand side =26 =2 x 4+18 =number ofH atoms on right-hand side

➤Questions often ask about the reactionbetweenbromine and alkene.

RemarksRemarks*

➤Questions often ask about the crackingprocess.

➤Crackingoccurswhen kerosenepasses over theunglazedporcelain.

➤Vaporization of keroseneoccurswhen theglasswool is heated.

No chemical reactionoccurs at theglass wool.

RemarksRemarks*

Example

Dodecane (C12H26)canbecracked intoetheneanda straight-chainalkaneXsuchthatthemole ratioof ethene : straight-chain alkaneX is 2:1.

a) Write a chemical equation for this reaction. (1mark)

b)A student performed an experiment to crack dodecane and collect the gaseousproducts byusing aboiling tube.

i) Thestudentaddedafewdropsofbrominedissolvedinanorganicsolventintotheboiling tubecontaining thegaseousproducts.Theorangecolourof thebrominesolutiondisappeared immediately.Why? (2marks)

ii)The student then dropped more bromine solution into the boiling tube untiltheorangecolourof thebrominesolutionpersisted.Afterabout10minutes, theorange colourdisappeared.Why? (2marks)

Answer

a) C12H26 2C2H4+C8H18 (1)

b)i) Theproducts of cracking contained alkenes / unsaturatedhydrocarbons (1)

whichdecolorized thebromine solution rapidlyby addition reaction. (1)

ii)Theproducts of cracking contained alkanes / saturatedhydrocarbons (1)

whichdecolorized thebromine solution slowlyby substitution reaction. (1)


28.1 Plastic items inmodernhomes

28.2 Why areplastics souseful?

28.3 What is apolymer?

28.4 Polymerization of ethene

28.5 The riseof themodernplastics industry

28.6 Addition polymerization

28.7 Some commonadditionpolymers

28.8 Uses of some commonadditionpolymers

28.9 Relating structures of thermoplastics to their thermalproperties

28.10 Economic importanceofplastics

28.11 Environmental issues associatedwith theuseofplastics

28.12 Common methods for treatingplasticwaste

28.13 Other possible solutions toplasticwastedisposal problems

28.14 The useofplastics forpackaging: anydisadvantages?

Addition polymersUnit 28

23Unit 28 Addition polymers

28.1 – 28.14

Summary

1 Petroleum is themost important rawmaterials used in theproductionofplastics.

2 Plasticsarepolymers.Apolymerisacompoundwhichconsistsofverylargemoleculesformedby joining togethermany smallmolecules repeatedly.

3 Polymerization is the process of repeatedly joining together many small moleculesto formvery largemolecules.

4 Arepeatingunitisthesmallestpartofapolymermolecule,andthewholepolymerstructure canbeobtainedby repeating it.

5 Addition polymerization is a reaction in which monomer molecules join togetherrepeatedlytoformpolymermolecules.Noatomsarelostfromthemonomermoleculesduring the reaction.

6 Some commonadditionpolymers are shownbelow:

Polymer Structure of monomer Structure of polymer

Lowdensitypolythene (LDPE)

H

H

C

H

H

C

H

H

C

H

H

C

n

Highdensitypolythene (HDPE)

H

H

C

H

H

C

H

H

C

H

H

C

n

Polypropene (PP)

H

H

C

H

CH3

C

H

H

C

H

CH3

C

n

Polyvinyl chloride(PVC)

Cl

H

C

H

H

C

Cl

H

C

H

H

C

n

Polystyrene (PS)

H

H

C

H

C

H

H

C

H

C

n

PerspexC O CH3

O

H

H

C

CH3

C

C O CH3

O

H

H

C

CH3

C

n

Theaboveadditionpolymersarethermoplastics.Theycanbemeltedorsoftenedbyheat at relatively low temperatures.


7 A comparisonofmethods for treatingplasticwaste.

Method for treating plastic waste Advantages Disadvantage(s)

Landfilling •alotofplasticwastecanbetreatedin a shortperiodof time

•does not cause much a i rpollution

•wasting land

•degradationofplastictakesalongtime

•m a y c a u s e p o l l u t i o n o fundergroundwater

•slowreleaseoftoxinsfromlandfillsites

Incineration •volume of solid waste can begreatly reduced

•energy canbeproduced

•reduce landwastage

•toxic gases areproduced

•thecostofoperatingacontrolledincinerationplant ishigh

Recycling •the amount of plastic waste canbe reduced

•conservepetroleumwhichisnon-renewable

•plastic waste can be convertedintousefulproducts

•it is difficult to separate plasticwaste fromotherwaste

•it isdifficult toseparatedifferentplasticwaste

•many plastics lose their originalpropertiesoversuccessiverecyclingcycles

•it isdifficult to removeadditivesinplasticwaste

•the process is uneconomical

Pyrolysis •conserve rawmaterials

•useful products (e.g. methane,ethene) canbeobtained

•a lot of energy is required

ExamtipsExamtipsExamtipsExamtips ♦ Questionsoftenaskabout theadvantagesofusingplasticsoverothermaterials formaking various objects.

e.g.

Suggest an advantage of using plastic over metal in making each ofthe following objects:

Object made Advantage of using plastic over metal

Casing for anelectric rice cooker

plastic canprevent electricity leakage

Drainagepipe plastic does not corrode

Helmet for soldier plastic has lowdensity

♦ Be careful with the term ‘addition polymerization’, NOT ‘additionalpolymerization’. ✔ ✘

♦ TheC=Cbonds inbenzeneandphenylgroupofaromaticcompoundsdoNOTundergo addition polymerization.

e.g.

CH2CH3

doesNOTundergo addition polymerization.

2�Unit 28 Addition polymers

Example

Manufacturerssometimesusepolyvinylchloride(PVC)tomakeproducts,suchaswaterpipes andwaterproofboots.

water pipe waterproof boots

a) i) Draw the structureof themonomerof PVC. (1mark)

ii)What characteristic in the structure of the monomer enables it to act as amonomer? (1mark)

♦ DoNOT confuse ‘monomer’with ‘repeatingunit’.

Whenasked togive the repeatingunitof apolymer,doNOTadd thevaluen.

✘

e.g.

the repeating unit of polythene is

H

H

C

H

H

C ,

NOT

H

H

C

H

H

C

n

.

✘

♦ When writing an equation for polymerization, remember to put thecoefficient ‘n’ in front of themonomer.

e.g.

CH3

H

H

C

H

C

n

polypropene

CH3

H

H

C

H

Cn

propene

♦ Spell the term ‘biodegradable’ correctly.

♦ Themajorityofhouseholdsolidwaste is treatedby landfillingwhereasthe rest is doneby recycling.

♦ Only thermoplastics are recycledby re-melting and re-shaping.

♦ Questions often ask students to compare the advantages anddisadvantages of possible methods for treatingplasticwaste.


b)Adding suitableplasticizers can reduce the rigidityofPVC, rendering it suitable formakingwaterproofboots.

plasticizer molecules

polymerchains

ExplainhowplasticizerscanhelpreducetherigidityofPVCintermsofintermolecularattractionsbetweenpolymer chains. (1mark)

c) Incineration is one of the ways to dispose of PVC waste. However, it may lead topollutionproblems.

i) SuggestTWOairpollutantsthatwillbeproducedduringtheincinerationofPVCwaste. (2marks)

ii) StateONEharmful effect of eachpollutant suggested in (i). (2marks)

iii) SuggestONEway to reduce the emissionof eachpollutant suggested in (i). (2marks)

Answer

a) i)

(1)

Cl H

C C

HH

ii)It contains carbon-carbondoublebond. (1)

b)Theintermolecularattractionsbetweenpolymerchainsweakenifthereareplasticizermolecules between thepolymer chains. (1)

c) i) Any twoof the following:

• Hydrogen chloride (1)

• Carbonmonoxide (1)

• Carbonparticles (1)

ii) Any twoof the following:

• Hydrogen chloride: irritant to the respiratory system / formationof acid rain (1)

• Carbonmonoxide: toxic (1)

• Carbonparticles: irritant to the respiratory system (1)

iii)Any twoof the following:

• Hydrogen chloride: installationof scrubbers (1)

• Carbonmonoxide: blasting air into the incinerator (1)

• Carbonparticles:installationofelectrostaticprecipitators/blastingairintotheincinerator (1)

2�Unit 28 Addition polymers

➤Questions often ask about PVC.

– PVC is a thermoplastic producedby additionpolymerization.

– ExamplesofflexibleproductsmadeofPVC—floortiles,showercurtains,raincoats,waterproof coating for folders andbags, insulating tapes andcoverings around electrical wires, seat coverings for taxis.

– Examples of rigid products madeof PVC—drain pipes andbottles.

RemarksRemarks*

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Topic Fossil Fuels and Carbon Compounds