NCERT Solutions for Class 12 Chemistry Chapter 15 Polymers

NCERT Solutions for Class 12 Chemistry Chapter 15 Polymers is prepared by experienced faculty of BYJU’S. The Solutions for Class 12 Chemistry Chapter 15 provides the answers to the textbook questions, exemplary questions, polymers class 12 important questions and worksheets which will help you to take polymers full chapter notes. Class 12 Chemistry Chapter 15 Polymers Solutions are given here for better understanding and clarification of the chapter.

Polymers are high molecular mass substances consisting of a very large number of simple repeating structural units joined together through covalent bonds in a regular fashion. Chapter 15 Polymers has been solved by expert teachers as per CBSE textbook guidelines. Students studying in class 12 have the pressure of scoring good marks in the board examination. To score good marks in the board examination one must solve the NCERT class 12th chemistry question papers.

Class 12 NCERT Solutions Chapter 15 – Polymers

NCERT Solutions for Class 12 Chemistry Chapter 15 includes the topics like – the terms Monomer, Polymer, Polymerisation. Classification of Polymers based on source: Natural polymers, Semi-synthetic polymers, Synthetic polymers. Classification of polymers based on structure: Linear Branched-chain, Cross-linked or Network Polymers. Classification of polymers based on the mode of polymerization: Addition polymers, Condensation polymers.

Classification of Polymers based on Molecular Forces:

Elastomers, Fibres, Thermoplastic And Thermosetting. Types of polymerization. The molecular mass of polymers. Biodegradable polymers. Two Greek words combine to form a term ‘polymer’. In Greek, ‘poly’ means many and ‘mers’ means part or unit. It is also referred to as macromolecules. Examples of polymers are Butadiene, Buna – N etc. Homo-polymers and Copolymers are two types of polymers which are based on their repeating structural unit. A chemical process to produce a chain-like structure or network of molecules called polymer by combining monomers is called polymerization.

There are two types of polymerization reactions:

  • Addition polymerization, It occurs in three steps:

Step 1: Chain initiation
Step 2: Chain propagation
Step 3: Chain termination

  • Condensation polymerization: It is also called as step-growth polymerization.

This was the introduction to the chapter 15th of chemistry class 12. Along with NCERT sample questions, one must solve previous year questions and participate in a mock test.

Subtopics of Class 12 Chemistry Chapter 15 – Polymers

  1. Classification of Polymers
  2. Types of Polymerisation Reactions
  3. Molecular Mass of Polymers
  4. Biodegradable Polymers
  5. Polymers of Commercial Importance

Class 12 Chemistry NCERT Solutions (Polymers) – Important Questions


Q1: Define the following terms: monomer and polymer.

Ans:

Polymers can be defined as a huge molecular mass macro-molecules made of repeating monomer-derived structural units. Polymers consists of a huge molecular mass of (103107u10^{3} -10^{7}u). Numerous units of monomers are combined together in one polymer by covalent bonds. The polymers either be both natural and synthetic. Examples of polymers include rubber, polythene, nylon 6, 6. Simple and reactive molecules, called monomers, fuse together in large groups by covalent bonds to produce polymers.

Eg: propene, ethene, vinyl chloride, styrene.

Q2: Explain synthetic polymers and natural polymers with the help of suitable examples of both the type?

Ans:

Polymers naturally found are known as Natural Polymer. Natural polymers are formed from animals and plants. Diverse natural polymer examples are protein, starch, cellulose, etc.

Polymers which are human-made are known as Synthetic Polymer. Various examples of the synthetic polymer are synthetic rubbers (Buna-5), synthetic fibres (nylon 6, 6), plastic (polythene).

Q3: Differentiate between homo-polymer and co-polymer by giving the example of both.

Ans:

HOMO-POLYMER CO-POLYMER
The polymerisation of a single monomer result in the creation of polymers called homo-polymers. Or put it another way, the repeating units of homo-polymers are formed from one monomer.

Example: homopolymer of ethane is polythene.

Co-polymers are polymers whose repeat units are obtained from two-type monomers.

Examples: Co-polymer of styrene and 1, 3 – butadiene is Buna – S.


Q4: Briefly explain the function of a monomer?

Ans:

The functional of a monomer may be defined as the total number of retaining sites, which are in this particular monomer.

For example, adipic acid and 1, 3-butadiene is two and that of propene and ethene is one

Q5: Explain the term polymerization.

Ans:

The mechanism of high molecular mass formation (103107u10^{3}-10^{7} u) macro-molecules, consisting of repeated structural units formed from monomers is known as polymerization. There are several monomer units in a polymer that are joined by tight covalent bonds.

Q6: Determine whether (NHCHRC0)n(-NH—CHR —C0-)_{n}, is a homo-polymer or a co-polymer?

Ans:

(NHCHRC0)n(-NH—CHR —C0-)_{n}  is a homo-polymer, the reason being that it is derived from a single monomer unit, NH2CHRCOOHNH_{2}—CHR—COOH.

Q7: Determine the groups where the polymers are graded according to molecular forces?

Ans:

Polymers are classified into groups given below based on the intermolecular magnitude of forces present in polymers:

(a) Fibres

(b) Elastomers

(c) Thermosetting polymers

(d) Thermoplastic polymers

Q8: Differentiate between condensation and addition polymerization?

Ans:

Condensation Polymerisation: The process in which the polymers are formed by the repeating condensation reactions between the two different bifunctional or trifunctional monomers. In this process molecules such as hydrochloric acid or water is eliminated.

For example, nylon 6, 6 is the result of adipic acid and hexamethylenediamine polymerization of the reaction condensation.

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Addition Polymerisation: The process in which, the monomers having double or triple bonds are added repeatedly to form polymers.

For example, Addition polymerization of ethene leads to the formation of Polyethene.

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Q9: Explain co-polymerization with the help of two examples.

Ans:

Co-polymerisation is the mechanism by which polymers are formed from two or more monomeric units. In a copolymer, there are multiple units of every monomer. Example of copolymerization is the process of forming polymer Buna-S from 1, 3-butadiene and styrene.

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The formation of copolymer Nylon 6, 6 is from adipic acid and hexamethylenediamine.

Q10: Explain free radical mechanism for polymerisation of the ethene.

Ans:

Ethene polymerization into polythene consists of exposing or heating as the initiator a mixture of ethene with a small amount of benzoyl peroxide to light.

Polymerization

 

Q 11: Define thermosetting and thermoplastics polymers? Give two examples of thermosetting and thermoplastics polymers?

Ans:
Thermosetting polymers are called polymers which are cross-linked or strongly branched polymers which are hardened during the moulding process. Through heating, they can not be softened yet again.
Eg: urea-formaldehyde resins, bakelite.

Thermoplastic polymers are called polymers which are linear slightly branched long-chain polymers which can be softened and hardened repeatedly when heated.

Eg: polystyrene, polythene.

Q 12: List out the monomers used for obtaining the below polymers.
(1) Polyvinyl chloride (2) Teflon (3) Bakelite

Ans:

(1) Vinyl chloride (CH2=CHClCH_{2}=CHCl)
(2) Tetrafluoroethylene (CF2=CF2CF_{2}= CF_{2})
(3) Phenol (C6H5OHC_{6}H_{5}OH) and Formaldehyde (HCHO)

Q 13: Write a common initiator’s name and structure used in free radical polymerization.

Ans:

Benzoyl peroxide is one of the common initiator’s name and structure used in free radical polymerization.

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Q 14: How do double bonds in the rubber molecules affect their structure and reactivity?

Ans:

Natural rubber is a linear cis-polyisoprene consisting of double bonds between the two units of isoprene C2  and  C3C_{2}\;and\;C_{3} .

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Intermolecular interactions between the different isoprene strands are relatively weak because of this cis-configuration. On account of this different natural rubber, strands are arranged randomly. So it’s showing elasticity.

Q 15: Discuss the main purpose of vulcanization of rubber.

Ans:

Natural rubber is useful, but its use does have problems. The disadvantages of natural rubber are as follows:
1. The natural rubber, at room temperature, is sticky and soft. It gets even softer at elevated temperatures, i.e. greater than 335 K. It becomes brittle at low temperatures, i.e. fewer than 283K. Therefore natural rubber can only be used to maintain its elasticity at a temperature range of 283 K-335 K.
2. Natural rubber absorbs a large amount of water
3. The natural rubber has low resistance to abrasion and low tensile strength.
4. Natural rubber is soluble in non-polar solvents.
5. Natural rubber ieasy to attack by oxidizing agents.

Vulcanization is done primarily to enhance natural rubber properties.

During this process, a mixture of raw rubber with sulphur and a suitable additive is heated to a temperature range of between 373 K and 415 K.

Q 16: Gives the Nylon-6 and Nylon-6, 6, monomeric repeating units?

Ans:
Nylon 6 monomeric repeat unit is [NH(CH2)5CO]\left[NH-(CH_{ 2 })_{ 5}-CO \right], derived from Caprolactam. The nylon 6, 6 monomeric repeat complex is [NH(CH)2)6NHCO(CH2)4CO]\left[NH-(CH)_{ 2 })_{ 6}-NH-CO-(CH_{ 2 })_{ 4}-CO\right], which is derived from diamine hexamethylene and adipic acid.

Q 17: List the names and the monomeric structures for the following polymers:
(i) Buna-S (ii) Buna-N
(iii) Dacron (iv) Neoprene

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Q 18: Identify the monomer underneath in polymer structures.

(i) 

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(ii)

3

Ans:

(i) Hexamethylene diamine is the monomer of the given polymeric structure

[H2N(CH2)6NH2]\left[H_{2}N(CH_{2})_{6}NH_{2} \right ] and decanoic acid
[HOOC(CH2)8COOH]\left[HOOC-(CH_{2})_{8}-COOH \right ].
(ii) The monomers of the polymeric structure given are:

 

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Q 19: How can dacron be obtained from terephthalic acid and ethylene glycol?

Ans:

Dacron is formed by the condensation polymerisation of terephthalic acid and ethylene glycol.

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Q 20: What is a Polymer that is biodegradable? Tell an example of a biologically degradable aliphatic polyester.

Ans:

A polymer which bacteria can decompose is called a Biodegradable Polymer. Poly-β-hydroxybutyrate-CO-β-hydroxyvalerate (PHBV) an example of an aliphatic biodegradable polyester.

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