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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