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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.
Topic 7� Fossil Fuels and Carbon Compounds
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.
Topic 7� Fossil Fuels and Carbon Compounds
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.
Topic 712 Fossil Fuels and Carbon Compounds
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*
Topic 71� Fossil Fuels and Carbon Compounds
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.
Topic 71� Fossil Fuels and Carbon Compounds
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
1�Unit 27 Alkanes and alkenes
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*
Topic 71� Fossil Fuels and Carbon Compounds
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
1�Unit 27 Alkanes and alkenes
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.
Topic 720 Fossil Fuels and Carbon Compounds
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)
Topic 722 Fossil Fuels and Carbon Compounds
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.
Topic 72� Fossil Fuels and Carbon Compounds
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.
Topic 72� Fossil Fuels and Carbon Compounds
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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