Nutrition and Digestion Chapter 41. Breaking It Down Major macromolecules: polymers monomers?
OSBINCBSE€¦ · CBSE Class–12 Subject Chemistry NCERT Solutions Chapter – 15 Polymers In-text...
Transcript of OSBINCBSE€¦ · CBSE Class–12 Subject Chemistry NCERT Solutions Chapter – 15 Polymers In-text...
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CBSEClass–12SubjectChemistry
NCERTSolutions
Chapter–15
Polymers
In-textQuestion
1.Whatarepolymers?
Ans. Polymers are high molecular mass macromolecules, which consist of repeating
structuralunitsderivedfrommonomers.Polymershaveahighmolecularmass(103-107u).
Inapolymer,variousmonomerunitsarejoinedbystrongcovalentbonds.Thesepolymers
can be natural as well as synthetic. Polythene, rubber, and nylon 6, 6 are examples of
polymers.
2.Howarepolymersclassifiedonthebasisofstructure?
Ans.Polymersareclassifiedonthebasisofstructureasfollows:
1.Linearpolymers:
Thesepolymersareformedoflongandstraightchains.
Thesepolymersarerepresentedas:
Fore.g.,highdensitypolythene(HDP),polyvinylchloride,etc.
2.Branchedchainpolymers:
Thesepolymersarebasicallylinearchainhavingsomebranches.
Thesepolymersarerepresentedas:
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Fore.g.lowdensitypolythene(LDP),glycogen,etc.
3.Cross-linkedorNetworkpolymers:
These polymers havemany cross-linking bonds that give rise to a network-like structure.
These polymers contain bi-functional and tri-functional monomers and strong covalent
bondsbetweenvariouslinearpolymerchains.
Thesepolymersarerepresentedas:
Examplesofsuchpolymersincludebakeliteandmalamine.
3. Classify the following as addition and condensation polymers: Terylene, Bakelite,
Polyvinylchloride,Polythene.
Ans.Additionpolymers:
Polyvinylchloride,polythene
Condensationpolymers:
Terylene,bakelite
4.Writethenamesofmonomersofthefollowingpolymers:
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Ans.(i)Hexamethylenediamine andadipicacid
(ii)
(iii)Tetrafluoroethene
5. Classify the following as addition and condensation polymers: Terylene, Bakelite,
Polyvinylchloride,Polyethene.
Ans.Additionpolymers:
Polyvinylchloride,polyethene
Condensationpolymers:
Terylene,bakelite
6.ExplainthedifferencebetweenBuna-NandBuna-S.
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Ans.Buna-Nisacopolymerof1,3-butadieneandacrylonitrile.
Buna-Sisacopolymerof1,3-butadieneandstyrene.
7.Arrangethefollowingpolymersinincreasingorderoftheirintermolecularforces.
(i)Nylon6,6,Buna-S,Polythene.
(ii)Nylon6,Neoprene,Polyvinylchloride.
Ans. Different types of polymers have different intermolecular forces of attraction.
Elastomers or rubbers have the weakest while fibres have the strongest intermolecular
forces of attraction. Plastics have intermediate intermolecular forces of attraction. Hence,
theincreasingorderoftheintermolecularforcesofthegivenpolymersisasfollows:
(i)Buna-S<polythene<Nylon6,6
(ii)Neoprene<polyvinylchloride<Nylon6
ChapterEndQuestion
1.Explainthetermspolymerandmonomer.
Ans. Polymers are the high molecular mass macromolecules composed of repeating
structuralunitsderivedfrommonomers.Polymershaveahighmolecularmass(103-107u).
Inapolymer,variousmonomerunitsarejoinedbystrongcovalentbonds.Polymerscanbe
naturalaswellassynthetic.Polythene,rubber,andnylon6,6areexamplesofpolymers.
Monomers are simple, reactivemolecules that combinewith each other in large numbers
throughcovalentbondstogiverisetopolymers.Forexample,ethene,propene,styrene,vinyl
chloride.
350-570K,1000-2000atatm
nCH2=CH2------------------tracesofO2-------------------------------->---(CH2-CH2)n----
EthenePolyethene
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(monomer)(polymer)
2.Whatarenaturalandsyntheticpolymers?Givetwoexamplesofeachtype.
Ans.Naturalpolymersarepolymersthatarefoundinnature.Theyareformedbyplantsand
animals.Examplesincludeprotein,cellulose.
Syntheticpolymersarepolymersmadebyhumanbeingsinthelaboratory.
Examplesincludeplastic(polythene),syntheticfibres(nylon6,6).
3.Distinguishbetweenthetermshomopolymerandcopolymerandgiveanexampleof
each.
Ans.
4.Howdoyouexplainthefunctionalityofamonomer?
Ans.Thefunctionalityofamonomeristhenumberofbindingsitesthatis/arepresentinthat
monomer.
Forexample,thefunctionalityofmonomerssuchasetheneandpropeneisoneandthatof1,
3-butadieneandadipicacidistwo.
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5.Definethetermpolymerisation.
Ans. Polymerization is the process of forming high molecular mass (103 - 107 u)
macromolecules called polymer, which consist of repeating structural units derived from
monomers.Inapolymer,variousmonomerunitsarejoinedbystrongcovalentbonds.
6.Is ,ahomopolymerorcopolymer?
Ans. isahomopolymerbecauseinittherepeatingstructuralunithas
onlyonetypeofmonomeri.e. -CHR-COOH.
7.Inwhichclasses,thepolymersareclassifiedonthebasisofmolecularforces?
Ans.Onthebasisofmagnitudeof intermolecular forcesofattractionpresent inpolymers,
theyareclassifiedintothefollowinggroups:
(i)Elastomers,example-bunaS
(ii)Fibres,example-nylon-6,6
(iii)Thermoplasticpolymers,example-polyethene
(iv)Thermosettingpolymers,example-bakelite
8.Howcanyoudifferentiatebetweenadditionandcondensationpolymerisation?
Ans. Addition polymerization is the process of repeated addition of same or different
monomer molecule, possessing double or triple bonds to form polymers. For example,
polytheneisformedbyadditionpolymerizationofethene.
Condensation polymerization is the process of formation of polymers by repeated
condensation reactions between two different bi-functional or tri-functionalmonomers. A
smallmoleculesuchaswaterorhydrochloricacid iseliminated ineachcondensation.For
example, nylon 6, 6 is formed by condensation polymerization of hexamethylenediamine
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andadipicacid.
9.Explainthetermcopolymerisationandgivetwoexamples.
Ans.Theprocessofformingpolymersfromtwoormoredifferentmonomericunitsiscalled
copolymerization.
Example-Theprocessof forming copolymerBuna-S from1, 3-butadieneand styrene is an
exampleofcopolymerization
Nylon6,6isalsoacopolymerformedbyhexamethylenediamineandadipicacid.
10.Writethefreeradicalmechanismforthepolymerisationofethene.
Ans.Polymerizationofethenetopolytheneconsistsofheatingorexposingtolightamixture
ofethenewithasmallamountofbenzoylperoxideastheinitiator.
Thereactioninvolvedinthisprocessisgivenbelow:
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ChapterEndQuestion
11.Definethermoplasticsandthermosettingpolymerswithtwoexamplesofeach.
Ans.Thermoplasticpolymersarelinear(slightlybranched)longchainpolymers,whichcan
be repeatedly softened onheating andhardened on cooling.Hence, they can bemodified
againandagain.Examplesincludepolythene,polystyrene.
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Thermosetting polymers are those polymers which on heating undergoes excessive cross
linkingandbecomehard.Thesepolymerscannotbesoftenedagainonheating.
Examplesofthermosettingpolymersincludebakelite,terylene.
12.Writethemonomersusedforgettingthefollowingpolymers.
(i)Polyvinylchloride
(ii)Teflon
(iii)Bakelite
Ans.(i)Vinylchloride
(ii)Tetrafluoroethene
(iii)Formaldehyde(HCHO)andphenol
13.Writethenameandstructureofoneofthecommoninitiatorsusedinfreeradical
additionpolymerisation.
Ans.Onecommoninitiatorusedinfreeradicaladditionpolymerizationisbenzoylperoxide.
Itsstructureisgivenbelow.
14. How does the presence of double bonds in rubber molecules influence their
structureandreactivity?
Ans.Natural rubber is a linear cis-polyisoprene in which the double bonds are present
between oftheisopreneunits.
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These cis-double bonds do not allow the polymer chains to come closer for effective
interactionsthereforethisintermolecularforceofinteractionsbetweenthevariousstrands
ofisopreneunitarequiteweak.Asaresult,variousstrandsinnaturalrubberarearranged
randomly.Hence,itshowselasticity.
15.Discussthemainpurposeofvulcanisationofrubber.
Ans. Natural rubber though useful has some problems associated with its use. These
limitationsarediscussedbelow:
1.Naturalrubberisquitesoftandstickyatroomtemperature.Atelevatedtemperatures(>
335K), it becomes even softer.At low temperatures (< 283K), it becomes brittle. Thus, to
maintain itselasticity,naturalrubber isgenerallyused in the temperaturerangeof283K-
335K.
2.Ithasthecapacitytoabsorblargeamountsofwater.
3.Ithaslowtensilestrengthandlowresistancetoabrasion.
4.Itissolubleinnon-polarsolvents.
5.Itiseasilyattackedbyoxidizingagents.
Vulcanizationofnaturalrubberisdonetoimproveuponalltheseproperties.Inthisprocess,
amixtureofrawrubberwithsulphurandappropriateadditiveisheatedatatemperature
rangebetween373Kand415K.
16.WhatarethemonomericrepeatingunitsofNylon-6andNylon-6,6?
Ans.Themonomericrepeatingunitofnylon-6is ,whichisderived
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fromCaprolactam.
The monomeric repeating unit of nylon 6, 6 is
, which is derived from hexamethylene
diamineandadipicacid.
17.Writethenamesandstructuresofthemonomersofthefollowingpolymers:
(i)Buna-S
(ii)Buna-N
(iii)Dacron
(iv)Neoprene
Ans.
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18.Identifythemonomerinthefollowingpolymericstructures.
(i)
(ii)
Ans.(i)Themonomersofthegivenpolymericstructurearedecanoicacid
andhexamethylenediamine .
(ii)Themonomersofthegivenpolymericstructureare
2,4,6-triamino-1,3,5-triazine Formaldehyde
19.Howisdacronobtainedfromethyleeglycolandterephthalicacid?
Ans.In thepresence of zinc acetate and antimony trioxide at 420-460K the condensation
polymerisationofethyleneglycolandterephthalicacidleadstotheformationofdacronwith
theremovalofwatermolecule.
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20.What is a biodegradable polymer? Give an example of a biodegradable aliphatic
polyester.
Ans.Apolymerthatcanbedecomposedbybacteriaiscalledabiodegradablepolymer.
Poly- -hydroxybutyrate-CO- - hydroxyvalerate (PHBV) is a biodegradable aliphatic
polyester.
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