NCERT Exemplar Problems Class 12 Chemistry Chapter 15 Polymers

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NCERT Exemplar Problems Class 12 Chemistry Chapter 15 Polymers

Multiple Choice Questions

Single Correct Answer Type
Question 1. Which of the following polymers of glucose is stored by animals?
(a) Cellulose (b) Amylose (c) Amylopectin (d) Glycogen
Solution: (d) Glycogen is a polymer of glucose found in liver, brain and muscles of animals. Cellulose is a polymer found in plant while amylase and amylopectin are structural units of starch.

Question 2. Which of the following is not a semisynthetic polymer?
(a) cis-polyisoprene (b) Cellulose nitrate
(c) Cellulose acetate (d) Vulcanised rubber
Solution: (a) m-polyisoprene is a natural polymer.

Question 3. The commercial name of polyacrylonitrile is
(a) Dacron (b) Orion (acrilan)
(d) Bakelite
Solution: (b) The commercial name of polyacrylonitrile is Orion or acrilan.

Question 4. Which of the following polymer is biodegradable?
Solution: (c)

Question 5. In which of the following polymers ethylene glycol is one of the monomer units?
Solution: (a) Given polymer can be obtained condensation polymerization of ethylene glycol and phthalic acid with the elimination of water molecule.

Question 6. Which of the following statements is not true about low density polythene?
(a) Tough (b) Hard
(c) Poor conductor of electricity (d) Highly branched structure
Solution: (b) Low density polythene is tough but flexible (not too hard) and a poor conductor of electricity. It has highly branched structure.

Question 7.
Solution: (a)

Question 8. Which of the following polymer can be formed by using the following monomer unit?
Solution: (d) Nylon -6 is the polymer formed by polymerisation of caprolactam.

More than One Correct Answer Type

Question 9. Which of the following polymers, need at least one diene monomer for their preparation?
(a) Dacron (b) Buna-S (c) Neoprene (d) Novolac
Solution: (b, c) Buna-S and neoprene are two such polymers which need at least one
diene monomer for their preparation.
(b) Buna-S is prepared by copolymerization of 1, 3-butadierie and styrene.

Question 10. Which of the following are characteristics of thermosetting polymers?
(a) Heavily branched cross linked polymers.
(b) Linear slightly branched long chain molecules.
(c) Become infusible on moulding so cannot be reused.
(d) Soften on heating and harden on cooling, can be reused.
Solution: (a, c) Thermosetting polymers are heavily branched cross linked polymers. They cannot be reused because they cannot melt on heating and cannot be remoulded.

Question 11. Which of the following polymers are thermoplastic?
(a) Teflon (b) Natural rubber (c) Neoprene (d) Polystyrene
Solution: (a, d) Teflon and polystyrene are thermoplastics since they can be moulded again by heating and melting.

Question 12. Which of the following polymers are used as fibre?
(a) Polytetrafluoroethane (b) Poly chloroprene
(c) Nylon (d) Terylene
Solution: (c, d) Nylon and terylene are used as fibres due to strong intermolecular forces like H-bonding which lead to close packing in chain and thus impart crystalline nature.

Question 13. Which of the following are addition polymers?
(a) Nylon (b) Melamine formaldehyde resin
(c) Orion (d) Polystyrene
Solution: (c, d) Orion and polystyrene are addition polymers made by polymerisation of CH2 = CH – CN (acrylonitrile) and, C6H5 – CH = CH2 styrene respectively.

Question 14. Which of the following polymers are condensation polymers?
(a) Bakelite (b) Teflon
(c) Butyl rubber (d) Melamine formaldehyde resin
Solution: (a, d) Bakelite is a condensation polymer of phenol and formaldehyde. Melamine formaldehyde resin is a condensation polymer of melamine (2, 4, 6-triamino-1, 3, 5-triazine) and formaldehyde.

Question 15. Which of the following monomers form biodegradable polymers?
(a) 3-hydroxybutanoic acid +3-hydroxypentanoic acid
(b) Glycine + aminocaproic acid
(c) Ethylene glycol + phthalic acid
(d) Caprolactam
Solution: (a, b) The polymers which are easily decomposed and not harmful for the environment are known as biodegradable polymer.
(i) PHBV is obtained by condensation polymerization of 3 hydroxybutanoic acid and 3 hxydroypentanoic acid.

Question 16. Which of the following are examples of synthetic rubber?
(a) Polychloroprene (b) Polyacrylonitrile
(c) Buna-N (d) cis-polyisoprene
Solution: (a, c)

Question 17. Which of the following polymers can have strong intermolecular forces?
(a) Nylon (b) Polystyrene (c) Rubber (d) Polyester
Solution: (a, d) Nylon and polyester are thread forming fibres which possesses high tensile strength and high melting point. They have strong intermolecular forces like hydrogen bonding.

Question 18. Which of the following polymers have vinylic monomer units?
(a) Acrilan (b) Polystyrene (c) Nylon (d) Teflon
Solution: (a, b, d) Acrilan, polystyrene and teflon has vinylic monomer units shown as follows:

Question 19. Vulcanisation makes rubber .
(a) more-elastic (b) soluble in inorganic solvent
(c) crystalline (d) more stiff
Solution: (a, d) Vulcanisation makes rubber more elastic and more stiff. On vulcanization sulphur forms cross links at the reactive sites of double bonds or at their reactive allylic position and thus rubber gets stiffened.

Short Answer Type Questions

Question 20. A natural linear polymer of 2-methyl-l,3-butadiene becomes hard on treatment with sulphur between 373 to 415 K and -S – S – bonds are formed between chains. Write the structure of the product of this treatment?
Solution: Vulcanized rubber.

Question 21. Identify the type of polymer.
Solution: It is a homopolymer, since its repeating structural unit is derived from only one type of monomer units, i.e., A.

Question 22. Identify the type of polymer.
Solution: It is a copolymer, since, its repeating structural unit is derived from two types of monomer units, i.e., A and B.

Question 23. Out of chain growth polymerisation and step growth polymerisation, in which type will you place the following.
Solution: It is an example of chain growth polymerisation, since in this polymerisation only addition occurs.

Question 24. Identify the type of polymer given in the following figure.
Solution: It is a cross linked polymer, since the various polymer chains are joined together to form a three-dimensional network structure (giant molecule).

Question 25. Identify the polymer given below:
Solution: The polymer is cis-polyisoprene (natural rubber), since the polymer is formed by 1, 4-addition of 2-methyl buta-1, 3-diene (isoprene).

Question 26. Why are rubbers called elastomers?
Solution: Rubbers are stretched on application of force and come to its original position after the force is removed. Therefore, these are called elastomers.

Question 27. Can enzyme be called a polymer?
Solution: Enzymes are biocatalysts which are proteins and thus can be called polymers.

Question 28. Can nucleic acids, proteins and starch be considered as step growth polymers?
Solution: Yes, step growth polymers (nucleic acids, proteins and starch) are conden¬sation polymers and they can be formed by the loss of simple molecule like water leading to the formation of high molecular mass polymers.

Question 29. How is the following resin intermediate prepared and which polymer is formed by this monomer unit?
Solution: Melamine and formaldehyde are starting materials for this intermediate. Its polymerisation gives melamine formaldehyde polymer.

Question 30. To have practical applications why are cross links required in rubber?
Solution: The cross links make the rubber hard, tough with greater tensile strength. The vulcanized rubber has excellent elasticity, low water absorption tendency, resistance to oxidation arid organic solvents.

Question 31. Why does cw-polyisoprene possess elastic property?
Solution: The cw-polyisoprene molecule consists of various chains held together by weal van der Waals interactions and has a coiled structure. Thus, it can be stretched like a spring and shows elastic properties.

Question 32. What is the structural difference between HDP and LDP? How does the structure account for different behaviour and nature, hence the use of a polymer?
Solution: LDP consists of highly branched chain molecules. Due to branching, the molecules do not pack well and therefore, it has low density (0.92 g cm 3) and low melting point. LDP is transparent of moderate tensile strength and high toughness. It is chemically inert.
HDP consists of linear chains and therefore, the molecules can closely pack in space. Therefore, it has high density (0.97 g cm 3) and high melting point. It is quite hard, tougher and has greater tensile strength than LDP.

Question 33. What is the role of benzoyl peroxide in addition polymerization of alkenes? Explain its mode of action with the help of an example.
Solution: Benzoyl peroxide acts as an initiator in free radical addition polymerisation of alkenes by providing chain initiation.
The radical formed adds to the carbon-carbon double bond of an alkene molecules and ultimately forms the polymer.
The new free radical adds to a double bond of monomer to form a larger free radical which adds to another alkene molecules and ultimately forms the polymer.

Question 34. Which factor imparts crystalline nature to a polymer like nylon?
Solution: Strong intermolecular forces like hydrogen bonding and linear structure lead to close packing of polymer chains that imparts crystalline character.

Question 35. Name the polymers used in laminated sheets and give the name of monomeric units involved in its formation.
Solution: The polymer is urea-formaldehyde resin

Question 36. Which type of biomolecules have some structural similarity with synthetic polyamides? What is this similarity?
Solution: Proteins have structural similarity with synthetic polyamides. Polyamides and proteins both contain amide linkage.

Question 37. Why should the monomers used in addition polymerisation through free radical pathway be very pure?
Solution: Pure monomers are required because even the traces of impurities may act as initiators which leads to the formation of polymers of small chain lengths.

Matching Column Type Questions

Question 38. Match the polymers of Column I with correct monomers of Column II.
Solution: (i —> e), (ii —» c), (iii —»a), (iv -» b), (v —»d)

Question 39. Match the polymers given in Column I with their chemical names given in Column II.
Solution: (i —> c), (ii —» a), (iii —»b), (iv -» e), (v —»d)

Question 40. Match the polymers given in Column I with their main applications given in Column II.
Solution: (i —» b), (ii —> c), (iii —> a), (iv —> e), (v -> d)

Question 41. Match the polymers given in Column I with their main applications given in Column II.
Solution: (i —> d), (ii —> e), (iii —» a), (iv —»f), (v —> b), (vi —» c)

Question 42. Match the polymers given in Column I with their main applications given in Column II.
Solution: (i —> d), (ii —> a), (iii —» b)

Question 43. Match the polymers given in Column I with the type of linkage present in them given in Column II.
Solution: (i —> b), (ii —> d), (iii —» a), (iv -> d), (v -» c)

Question 44. Match materials given in Column I with the polymers given in Column II.
Solution: (i —> f), (ii -» e), (iii —» a), (iv —> c), (v —> b), (vi —> d)

Question 45. Match the polymers given in Column I with their repeating units given in Column 11.
Solution: (i —> d), (ii —> a), (iii —> b),(iv -> e),(v -> c)

Assertion and Reason Type Questions

In the following questions, a statement of Assertion (A) followed by a statement of
Reason (R) is given. Choose the correct answer out of the following choices:
(a) Assertion and Reason both are correct statements but Reason is not the correct explanation of Assertion.
(b) Assertion and Reason both are correct statements and Reason is the correct explanation of Assertion.
(c) Both Assertion and Reason are false.
(d) Assertion is correct but Reason is false.
(e) Assertion is false but Reason is correct.

Question 46. Assertion (A): Rayon is a semi-synthetic polymer and is taken as a better choice than cotton fabric.
Reason (R): Mechanical and aesthetic properties of cellulose can be improved by acetylation.
Solution: (b) Rayon is semi-synthetic polymer and is a better choice than cotton because properties of cellulose are improved by acetylation while processing.

Question 47. Assertion (A): Most of the synthetic polymers are not biodegradable.
Reason (R): Polymerisation process induces toxic character in organic molecules.
Solution: (d) Most of the synthetic polymers are not degraded by enzymatic hydrolytic and environmental oxidation. Polymerisation does not induce toxic characters.

Question 48. Assertion (A): Olefinic monomers undergo addition polymerization.
Reason (R): Polymerisation of vinyl chloride is initiated by peroxides/ persulphates.
Solution: (a) Olefins like ethene undergo addition polymerization to give polymer like polythene.

Question 49. Assertion (A): Polyamides are best used as fibres because of high tensile strength.
Reason (R): Strong intermolecular forces (like hydrogen bonding within polyamides) lead to close packing of chains and increase the crystalline character, hence, provide high tensile strength to polymers.
Solution: (b) Polyamides like nylons are best used fibres. They have high tensile strength due to presence of strong inter molecular hydrogen bond.

Question 50. Assertion (A): For making rubber synthetically, isoprene molecules are polymerised.
i Reason (R): Neoprene (a polymer of chloroprene) is a synthetic rubber.
Solution: (e) Isoprene molecule is the monomer for natural rubber, while neoprene a synthetic rubber is formed by polymerisation of chloroprene.

Question 51. Assertion (A): Network polymers are thermosetting.
Reason (R): Network polymers have high molecular mass.
Solution: (a) Extensive cross linking during polymerisation leads to the formation of three-dimensional network which is hard, infusible and insoluble.

Question 52. Assertion (A): Polytetrafluoroethene is used in making non-stick cookware. Reason (R): Fluorine has highest electronegativity.
Solution: (a) Teflon is used in making nonstick cookware as it is chemically inert and thermally stable.

Long Answer Type Questions

Question 53. Synthetic polymers do not degrade in the environment for a long time. How can biodegradable synthetic polymers be made. Differentiate between biopolymers and biodegradable polymers and give examples of each type.
Solution: Synthetic polymers are quite resistant to environmental degradation process and are responsible for accumulation of polymer solid waste material. New biodegradable synthetic polymers have been designed and developed. These polymers contain similar functional groups as present in biopolymers, e.g., aliphatic polyesters
Biopolymers are polymers of amino acids or carbohydrates which are linked to each other by peptide or glycosidic linkages as shown below
Polymer of amino acid Biopolymer can or cannot be biodegradable.
e.g., protein, starch etc., are biodegradable but keratin are non-biodegradable. Biodegradable polymer are polymers which can be degradable always, e.g., DHBV nylon-2, nylon-6.

Question 54. Differentiate between rubbers and plastics on the basis of intermolecular forces.
Solution: Rubber is a natural polymer which is capable of returning to its original
length, shape or size after being stretched or deformed. It is a common example of an elastomer. The m-polyisoprene molecule (natural rubber) consists of various chains held together by weak van der Waals interactions and has a coiled structure.
Thermoplastics are the polymers in which intermolecular forces of attraction are in between those of elastomers and fibres. They are neither very strong nor very weak and have no cross links between the chains molecules capable of repeatedly softening on heating and hardening on cooling.

Question 55. Phenol and formaldehyde undergo condensation to give a polymer (A) which on heating with formaldehyde gives a thermosetting polymer (B). Name the polymers. Write the reactions involved in the formation of (A). What is the structural difference between two polymers?
Solution: Polymer ‘A’ is Novalac and‘‘B’ is Bakelite. The reactions involved in the formation of these two polymers are given below:
Novalac on heating with HCHO undergo cross-linkage to form an infusible solid called Bakelite.
Novolac is linear chain polymer while Bakelite is cross linked polymer.

Question 56. Low density polythene and high density polythene, both are polymers of ethane but there is marked difference in their properties. Explain.
Solution: Low density and high density polythenes are obtained under different reaction conditions. LDP is obtained through free radical addition at high pressure (1000 to 2000 atm) and a temperature of 350 K to 570 K and is highly branched structure. LDP is chemically inert and tough but slightly flexible.
High density polythene or HDP is obtained by addition polymerisation of ethene in presence of hydrocarbon solvent at low pressure of hydrocarbon solvent at low pressure (6-7 atm) and a temperature of 333 K to 343 K in presence of Ziegler-Natta catalyst. Under these conditions the polymer is linear and has high density due to close packing. It is tougher, and harder than LDP.

Question 57. Which of the following polymers soften on heating and harden on cooling? What are the polymers with this property collectively called? What are the polymers with this property collectively called? What are the structural similarities between such polymers? Bakelite, urea-formaldehyde resin, polythene, polyvinyl, polystyrene.
Solution: Polythene, polyvinyl and polystyrene soften on heating and harden on cooling. Such polymers are called thermoplastic polymers. These possess intermolecular forces of attraction whose strength lies between strength of intermolecular forces of elastomers and fibres. These polymers are linear or slightly branched long chain molecules.

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