NCERT Exemplar Class 12 Chemistry Solutions Chapter 15 Polymers

Question 1. Which of the following polymers of glucose is stored by animals?
(i) Cellulose
(ii) Amylose
(iii) Amylopectin
(iv) Glycogen

Answer:

The answer is the option (iv). Amongst the given options, glycogen is a polymer of glucose that is found in liver, brain and muscles of animals.

Question 2. Which of the following is not a semisynthetic polymer?
(i) cis-polyisoprene
(ii) Cellulose nitrate
(iii) Cellulose acetate
(iv) Vulcanised rubber

Answer:

The answer is the option (i). Of all the given options, Cis-polyisoprene is not a semisynthetic polymer. m-polyisoprene is a natural polymer while the others are semisynthetic polymers.

Question 3. The commercial name of polyacrylonitrile is ______________.
(i) Dacron
(ii) Orlon (Acrilan)
(iii) PVC
(iv) Bakelite

Answer:

The answer is the option (ii). The commercial name of polyacrylonitrile is Orion (acrilan). It is used as a substitute for wool in making commercial fibres.

Question 4. Which of the following polymer is biodegradable?

Answer:

The answer is the option (iii). PHBV is biodegradable in nature. It is formed by the copolymerisation of 3-hydroxybutanoic acid and 3-hydroxypentanoic acid.

Question 5. In which of the following polymers ethylene glycol is one of the monomer units?

Answer:

The answer is the option (i). The polymer given below is obtained on condensation polymerisation of ethylene glycol and phthalic acid. The water molecule gets eliminated in the process.

Question 6. Which of the following statements is not true about low-density polythene?
(i) Tough
(ii) Hard
(iii) Poor conductor of electricity
(iv) Highly branched structure

Answer:

The answer is the option (iii). We can obtain low-density polythene by polymerisation of ethane under high pressure. It tough but flexible (not too hard) in nature and has a highly branched structure.

Question 7.

is a polymer having monomer units ____________.

Answer:

The answer is the option (i).

Question 8. Which of the following polymer can be formed by using the following monomer unit?

(i) Nylon 6, 6
(ii) Nylon 2–nylon 6
(iii) Melamine polymer
(iv) Nylon-6

Answer:

The answer is the option (iv). Nylon -6 is the polymer formed by heating caprolactam with water at a high temperature.

NCERT Exemplar Solutions Class 12 Chemistry Chapter 15: MCQ (Type 2)

All the MCQ (type 2) questions with solutions are given below:

Question 9. Which of the following polymers, need at least one diene monomer for their preparation?
(i) Dacron
(ii) Buna-S
(iii) Neoprene
(iv) Novolac

Answer:

The answer is the option (ii, iii) Buna-S and neoprene need at least one diene monomer in their preparation. Buna-S is prepared by copolymerisation of 1, 3-butadiene and styrene in the presence of peroxide catalyst.

Neoprene is formed by the free radical polymerisation of chloroprene.

Question 10. Which of the following are characteristics of thermosetting polymers?
(i) Heavily branched cross-linked polymers.
(ii) Linear slightly branched long-chain molecules.
(iii) Become infusible on moulding so cannot be reused.
(iv) Soften on heating and harden on cooling, can be reused.

Answer:

The answer is the option (i, iii) Thermosetting polymers or thermoset are heavily branched and cross-linked molecules. They cannot be reused as they become infusible on the moulding.

Question 11. Which of the following polymers are thermoplastic?
(i) Teflon
(ii) Natural rubber
(iii) Neoprene
(iv) Polystyrene

Answer:

The answer is the option (i, iv) Thermoplastic polymers can be repeatedly softened on heating and hardened on cooling. Thus, they can be remoulded again and again. Teflon and polystyrene are common examples of thermoplastics.

Question 12. Which of the following polymers are used as fibre?
(i) Polytetrafluoroethane
(ii) Polychloroprene
(iii) Nylon
(iv) Terylene

Answer:

The answer is the option (iii, iv) Fibres have high tensile strength and modulus due to strong intermolecular forces like H-bonding. This leads to close packing in chain resulting in crystalline nature. Polyamides (Nylon) and Polyesters (terylene) are used as fibres.

Question 13. Which of the following are addition polymers?
(i) Nylon
(ii) Melamine formaldehyde resin
(iii) Orlon
(iv) Polystyrene

Answer:

The answer is the option (iii, iv) Orion and polystyrene are examples of addition polymers formed by repeated addition of monomer molecules. Orion is made by polymerisation of ${\text{CH }}_2=\text{ CH - CN (acrylonitrile)}$ and polystyrene by ${\text{C}}_6{\text{H}}_5-{\text{CH=CH}}_2\text{(styrene)}$

Question 14. Which of the following polymers are condensation polymers?
(i) Bakelite
(ii) Teflon
(iii) Butyl rubber
(iv) Melamine formaldehyde resin

Answer:

The answer is the option (i, iv) Phenol when heated with formaldehyde gives an infusible solid mass known as bakelite. On condensation polymerisation of melamine and formaldehyde, melamine formaldehyde resin is obtained.

Question 15. Which of the following monomers form biodegradable polymers?
(i) 3-hydroxybutanoic acid + 3-hydroxypentanoic acid
(ii) Glycine + aminocaproic acid
(iii) Ethylene glycol + phthalic acid
(iv) Caprolactam

Answer:

The answer is the option (i, ii) The polymers which are easily decomposed are known as biodegradable polymer. PHBV is biodegradable in nature. It is formed by the copolymerisation of 3-hydroxybutanoic acid and 3-hydroxypentanoic acid. Glycine + amino caproic acid on copolymerisation give Nylon-2-nylon 6 which is also biodegradable.

Question 16. Which of the following is an example of a synthetic rubber?
(i) Polychloroprene
(ii) Polyacrylonitrile
(iii) Buna-N
(iv) cis-polyisoprene

Answer:

The answer is the option (i, iii)
Polychloroprene is a polymer of chloroprene and it is synthetic rubber.

Question 17. Which of the following polymers can have strong intermolecular forces?
(i) Nylon
(ii) Polystyrene
(iii) Rubber
(iv) Polyesters

Answer:

The answer is the option (i, iv). Polyamides (Nylon) and Polyesters (terylene) have high tensile strength and modulus due to strong intermolecular forces like H-bonding. This leads to close packing in the chain resulting in crystalline nature. That is why they are used as thread forming fibres.

Question 18. Which of the following polymers have vinylic monomer units?
(i) Acrilan
(ii) Polystyrene
(iii) Nylon
(iv) Teflon

Answer:

The answer is the option (i, ii, iv) Amongst the given options, acrilan, polystyrene and Teflon has vinylic
Monomer units.

Question 19. Vulcanisation makes rubber ______________.
(i) more elastic
(ii) soluble in inorganic solvent
(iii) crystalline
(iv) more stiff

Answer:

The answer is the option (i, iv). Vulcanisation is a chemical process wherein rubber is heated with Sulphur to form cross-links between rubber molecules. The process is carried to improve the physical properties like elasticity of natural rubber. It makes the rubber stiffer.

NCERT Exemplar Solutions Class 12 Chemistry Chapter 15: Short Answer Type

All the short-answer type questions with solutions are given below:

Question 20. A natural linear polymer of $\text{2-methyl-1, 3-butadiene}$ becomes hard on treatment with sulphur between 373 to 415 K and $\text{-S-S-}$ bonds are formed between chains. Write the structure of the product of this treatment?

Answer:

The structures of the Vulcanised rubber molecules are as given below.

Question 21. Identify the type of polymer.
$\text{-A-A-A-A-A-A-}$

Answer:

Polymerisation of single monomeric species (one type of monomer unit) gives homopolymers. In this case the unit is A.

Question 22. Identify the type of polymer.
$\text{-A-B-B-A-A-A-B-A-}$

Answer:

Polymers wherein repeating structural unit has 2 types of monomer units (let’s say A and B) are known as copolymers.

Question 23. Out of chain growth polymerisation and step-growth polymerisation, in which type willyou place the following.

Answer:

It is a type of chain growth polymerisation because only addition occurs in this.

Question 24. Identify the type of polymer given in the following figure.

Answer:

The polymer given in the diagram is a cross linked polymer because a 3- D network structure (giant molecule) is formed from various polymer chains.

Question 25. Identify the polymer given below :

Answer:

The polymer given is cis-polyisoprene (natural rubber) and has a coiled structure. It shows elastic properties as well.

Question 26. Why are rubbers called elastomers?

Answer:

Rubber is a natural polymer with elastic properties, i.e. it stretches and relaxes with the application or removal of external force. That is why these are called elastomers.

Question 27. Can the enzyme be called a polymer?

Answer:

Since enzymes are biocatalysts that are basically proteins, they can be called polymers.

Question 28. Can nucleic acids, proteins and starch be considered as step growth polymers?

Answer:

Step growth polymers are formed by condensation polymerisation reaction resulting in the loss of simple molecule like water, alcohol that in turn, results in the formation of high molecular mass polymers. Nucleic acids, proteins and starch are formed in the same way. Hence, they can be considered as step-growth polymers.

Question 29. How is the following resin intermediate prepared and which polymer is formed by this monomer unit?

Answer:

The given intermediate is formed by the condensation polymerisation of melamine and formaldehyde. Its polymerisation gives melamine formaldehyde.

Question 30. To have practical applications, why are cross-links required in rubber?

Answer:

Cross-links are formed in the process of vulcanisation which is done to improve the physical properties of natural rubber. By cross-linking, rubber gets hard and tough due to increased tensile strength. The vulcanised rubber has higher elasticity, increased stiffness and low water absorption tendency.

Question 31. Why does cis-polyisoprene possess elastic property?

Answer:

The cis-polyisoprene molecule has a coiled structure. In it, several chains are held together by weak van der Waals interactions. This is why they possess elastic property.

Question 32. What is the structural difference between $\text{HDP}$ and $\text{LDP}$? How does the structure account for different behaviour and nature, hence the use of a polymer?

Answer:

$\text{LDP}$ or Low-density polythene has a highly branched molecular structure. It has low density (0.92 g/cm 3) and low melting point, as the molecules do not pack well due to branching. It is transparent and chemically inert with moderate toughness.
$\text{HDP}$ or High-density polythene has linear chains, and thus the molecules are closely packed in space. Therefore, it has a higher density and melting point. In comparison to $\text{LDP}$, it is harder, tougher and has greater tensile strength.

Question 33. What is the role of benzoyl peroxide also polymerisation of alkenes? Explain its mode of action with the help of an example.

Answer:

The role of Benzoyl peroxide in free radical addition polymerisation of alkenes is to generate free radicals and act as an initiator of the reaction by providing chain initiation.

The free radical is added to the double bond of an alkene molecule forming the polymer.

The new free radical is added to a double bond of monomer to form a larger free radical, which when added to other alkene molecules forms the polymer.

Lastly chain termination step-

Question 34. Which factor imparts crystalline nature to a polymer like nylon?

Answer:

Polymers like nylon have strong intermolecular forces like hydrogen bonding that lead to close packing of polymer chains. This, along with the linear structure, gives a crystalline nature to the polymer.

Question 35. Name the polymers used in laminated sheets and give the name of monomeric units involved in its formation.

Answer:

The polymer is a urea-formaldehyde resin and the monomeric units are urea and formaldehyde.

Question 36. Which type of biomolecules has some structural similarity with synthetic polyamides? What is this similarity?

Answer:

The biomolecules having some structural similarity with synthetic polyamides are protein. The similarity is that the polyamides and proteins both contain amide linkage.

Question 37. Why should the monomers used in addition polymerisation through free radical pathway be very pure?

Answer:

The monomers used in addition polymerisation through free radical should be very pure because even a tiny amount of impurities may act as initiators leading to the formation of polymers with small chain lengths.

NCERT Exemplar Solutions Class 12 Chemistry Chapter 15: Matching Type

All the matching type questions with solutions are given below:

Question 38. Match the polymer of column I with a correct monomer of column II.

Answer:

(i $\to$ e), (ii $\to$ c), (iii $\to$a), (iv $\to$ b), (v $\to$d)

Question 39. Match the polymers given in Column I with their chemical names given in Column II.

Answer:

(i $\to$ c), (ii $\to$ a), (iii $\to$ b), (iv $\to$ e), (v $\to$ d)

Question 40. Match the polymers given in Column I with their commercial names given in Column II.

Answer:

(i $\to$ b), (ii $\to$ c), (iii $\to$ a), (iv $\to$ e), (v $\to$ d)

Question 41. Match the polymers given in Column I with their main applications given in Column II.

Answer:

(i $\to$ d), (ii $\to$ e), (iii $\to$ a), (iv $\to$ f), (v $\to$ b), (vi $\to$ c)

Question 42. Match the polymers given in Column I with the preferred mode of polymerisation followed by their monomers.

Answer:

(i $\to$ d), (ii $\to$ a), (iii $\to$ b)

(i) Nylon-6,6 follows condensation polymerisation. Each time a molecule of the diamine reacts with a molecule of the diacid, an amide bond (–CO–NH–) is formed and a water molecule is eliminated.

(ii) The monomer unit of PVC is vinyl chloride. Under pressure, heat, and the presence of a free radical initiator, vinyl chloride monomers undergo free radical addition polymerisation.

(iii) High-Density Polyethene (HDP) is a widely used plastic made by the polymerisation of ethene (ethylene) monomers. HDP follows Coordination polymerisation, carried out using Ziegler–Natta catalyst.

Question 43. Match the polymers given in Column I with the type of linkage present in they have given in Column II.

Answer:

(i $\to$ b), (ii $\to$ d), (iii $\to$ a), (iv $\to$ d), (v $\to$ c)

(i) Terylene is formed by condensation polymerisation of terephthalic acid and ethylene glycol. Each unit forms an ester linkage with the elimination of water.

(ii) Nylon is formed by condensation polymerisation of hexamethylenediamine and adipic acid, forming an amide bond (–CO–NH–) with the elimination of water. Therefore, amide linkage is present in nylon.

(iii) Cellulose is a natural polysaccharide made up of repeating units of β-D-glucose. The hydroxyl group (-OH) on carbon 1 (C₁) of one glucose reacts with the –OH on carbon 4 (C₄) of the next glucose. This forms a glycosidic bond.

(iv) Proteins are natural polymers made up of amino acids. A (–CO–NH–) bond is formed between the carboxyl group of one amino acid and the amino group of another. Therefore, amide linkage is present in proteins.

(v) RNA is a nucleic acid polymer made up of nucleotides. It consists of ribose sugar, a phosphate group and a nitrogenous base. The phosphate group of one nucleotide forms two ester bonds, one with the 3′-OH group and another with the 5′-OH group. Therefore, 3′-5′ phosphodiester linkage is present in RNA.

Question 44. Match materials are given in Column I with the polymers given in Column II.

Answer:

(i $\to$ f), (ii $\to$ e), (iii $\to$ a), (iv $\to$ c), (v $\to$ b), (vi $\to$ d)

Question 45. Match the polymers given in Column I with their repeating units given in Column II

Answer:

(i $\to$ d), (ii $\to$ a), (iii $\to$ b), (iv $\to$ e),(v $\to$ c)

NCERT Exemplar Solutions Class 12 Chemistry Chapter 15: Assertion and Reason Type

All the assertion-reason type questions with solutions are given below:

Question 46. In the following question a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices.
Assertion: Rayon is a semi-synthetic polymer and is taken as a better choice than cotton fabric.
Reason: Mechanical and aesthetic properties of cellulose can be improved by acetylation.
(i) Assertion and reason both are correct statements, but reason does not explain the assertion.
(ii) Assertion and reason both are correct statements, and reason explain the assertion.
(iii) Both assertion and reason are the wrong statements.
(iv) The assertion is correct statement and reason is the wrong statement.
(v) The assertion is the wrong statement and reason is the correct statement.

Answer:

The answer is the option (ii). Rayon is semi-synthetic polymer and is taken as a better choice than cotton fabric because mechanical and aesthetic properties of cellulose can be improved by acetylation. Thus, both assertion and reason are correct with the latter being the correct explanation.

Question 47. In the following question a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices.
Assertion: Most of the Synthetic polymers are not biodegradable.
Reason: Polymerisation process induces toxic character in organic molecules.
(i) Assertion and reason both are correct statements, but reason does not explain the assertion.
(ii) Assertion and reason both are correct statements, and reason explain the assertion.
(iii) Both assertion and reason are the wrong statements.
(iv) The assertion is correct statement and reason is the wrong statement.
(v) The assertion is the wrong statement and reason is the correct statement.

Answer:

The answer is the option (iv). Most of the synthetic polymers are non-biodegradable in nature i.e. they are not degraded by enzymatic, hydrolytic and environmental oxidation. Polymerisation process does not induce toxic characters in organic molecules.

Question 48. In the following question a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices.
Assertion: Olefinic monomers undergo addition polymerisation.
Reason: Polymerisation of vinyl chloride is initiated by peroxides/persulphates.
(i) Assertion and reason both are correct statements, but reason does not explain the assertion.
(ii) Assertion and reason both are correct statements, and reason explain the assertion.
(iii) Both assertion and reason are the wrong statements.
(iv) The assertion is correct statement and reason is the wrong statement.
(v) The assertion is the wrong statement and reason is the correct statement.

Answer:

The answer is the option (i). Olefinic monomers like ethene undergo addition polymerisation. The monomers used in addition polymerisation reaction are unsaturated compounds like alkenes, alkadienes etc. The assertion and reason both are correct statements but the reason does not explain the assertion.

Question 49. In the following question a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices.
Assertion: Polyamides are best used as fibres because of high tensile strength.
Reason: 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.
(i) Assertion and reason both are correct statements, but reason does not explain the assertion.
(ii) Assertion and reason both are correct statements, and reason explain the assertion.
(iii) Both assertion and reason are the wrong statements.
(iv) The assertion is correct statement and reason is the wrong statement.
(v) The assertion is the wrong statement and reason is the correct statement.

Answer:

The answer is the option (ii). Polyamides are best-used fibers because they have high tensile strength. They have closely packed chains and increased crystalline character due to presence of strong inter molecular forces like hydrogen bonding.

Question 50. In the following question a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices.
Assertion: For making rubber synthetically, isoprene molecules are polymerised.
Reason: Neoprene (a polymer of chloroprene) is a synthetic rubber.
(i) Assertion and reason both are correct statements, but reason does not explain the assertion.
(ii) Assertion and reason both are correct statements, and reason explain the assertion.
(iii) Both assertion and reason are the wrong statements.
(iv) The assertion is correct statement and reason is the wrong statement.
(v) The assertion is the wrong statement and reason is the correct statement.

Answer:

(v) Isoprene (2-methyl-1,3-butadiene) molecule is the monomer for natural rubber. Neoprene (a polymer of chloroprene) is a synthetic rubber.

Question 51. In the following question a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices.
Assertion: Network polymers are thermosetting.
Reason: Network polymers have high molecular mass.
(i) Assertion and reason both are correct statements, but reason does not explain the assertion.
(ii) Assertion and reason both are correct statements, and reason explain the assertion.
(iii) Both assertion and reason are the wrong statements.
(iv) The assertion is correct statement and reason is the wrong statement.
(v) The assertion is the wrong statement and reason is the correct statement.

Answer:

The answer is the option (i). Network polymers are thermosetting and have high molecular mass. However, the reason they are thermosetting is because of extensive cross-linking during polymerisation and not because of higher molecular mass.

Question 52. In the following question a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices.
Assertion: Polytetrafluoroethene is used in making non-stick cookware.
Reason: Fluorine has the highest electronegativity.
(i) Assertion and reason both are correct statements, but reason does not explain the assertion.
(ii) Assertion and reason both are correct statements, and reason explain the assertion.
(iii) Both assertion and reason are the wrong statements.
(iv) The assertion is correct statement and reason is the wrong statement.
(v) The assertion is the wrong statement and reason is the correct statement.

Answer:

The answer is the option (i). Polytetrafluoroethene or Teflon is used in making nonstick cookware, as it is chemically inert, resistant to attack by corrosive reagents and thermally stable.

NCERT Exemplar Solutions Class 12 Chemistry Chapter 15: Long Answer Type

All the long-answer type questions with solutions are given below:

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.

Answer:

Synthetic polymers are non-biodegradable as they are resistant to the environmental degradation process. They form a major share of the polymer solid waste material.
Biopolymers are natural polymers of amino acids or carbohydrates, linked together by peptide or glycosidic linkages. They are found in plants and animals.

Biopolymers may or may not be biodegradable. For example, while protein and starch are biodegradable, keratin is not. Biodegradable polymer is a polymer which are not resistant to the environmental degradation process, e.g., DHBV nylon-2, nylon-6. Both the biodegradable polymers and biopolymers contain similar functional groups.

Question 54. Differentiate between rubbers and plastics on the basis of intermolecular forces.

Answer:

Question 55. Phenol and formaldehyde undergo condensation to give a polymar (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?

Answer:

Polymer ‘A’ in the question is Novalac and ‘B’ is bakelite. The reactions involved are:

The main structural difference between them is that novolac is a linear chain polymer while bakelite is a 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.

Answer:

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.

Answer:

Thermoplastic polymers soften on heating and harden on cooling. Polythene, polyvinyl and polystyrene are thermoplastic polymers. Their intermolecular force of attraction is somewhere between elastomers and fibres. They soften on heating and harden on cooling.
Bakelite, urea-formaldehyde resin are examples of thermosetting polymers. They are cross-linked and cannot be reused.