# NCERT Solutions for Class 12 Chemistry Chapter 15 Polymers

## NCERT Solutions For Class 12 Chemistry Chapter 15 PDF Free Download

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
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 macro-molecules having high molecular mass, which is made of repeating structural units derived from monomers. Polymers consists of a high molecular mass ($10^{3} -10^{7}u$). In one polymer, numerous monomer units are combined together by strong covalent bonds. Polymers can be both synthetic and natural. Rubber, polythene and nylon 6, 6 are examples of polymers. Simple and reactive molecules called monomers, fuse with each other in large groups through covalent bonds to give rise to polymers. Eg: propene, ethene, vinyl chloride, styrene.

Q2: Explain natural and synthetic polymers with the help of two examples of each type?

Ans:

Polymers that are found in nature are called Natural Polymer. They are formed from plants and animals. Various examples of the natural polymer are protein, starch, cellulose, etc.

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

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

Ans:

 HOMO-POLYMER CO-POLYMER Polymerization of a single monomer leads to the formation of polymers which are known as homo-polymers. In other words, from one monomer, the repeating units of homo-polymers are formed. Example: homopolymer of ethane is polythene. Co-polymers are polymers whose repeating units are derived from monomers which are of two types. Examples: Co-polymer of 1, 3 – butadiene and styrene 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 binding sites, which are present in that 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 process of forming a high molecular mass ($10^{3}-10^{7} u$) macro-molecules, consisting of repeated structural units formed or derived from monomers is known as polymerization. Various monomer units are joined by strong covalent bonds in a polymer.

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

Ans:

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

Q7: Determine the classes in which the polymers are classified on the basis of molecular forces?

Ans:

On the basis of intermolecular forces magnitude present in polymers, polymers are classified in groups given below:

(i) Elastomers

(ii) Fibres

(iii) Thermosetting polymers

(iv) 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 condensation polymerization of hexamethylenediamine and adipic acid.

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.

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

Ans:

Co-polymerisation is the process of forming polymers from two or more different monomeric units. In a copolymer, multiple units of each monomer are present. Example of copolymerization is the process of forming polymer Buna-S from 1, 3-butadiene and styrene.

Nylon 6, 6 a copolymer formed by hexamethylenediamine and adipic acid.

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

Ans:
Polymerization of ethene to polythene consists of heating or exposing to light a mixture of ethene with a small amount of benzoyl peroxide as the initiator.

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

Ans:
Polymers which are cross-linked or heavily branched polymers which get
hardened during the moulding process are called thermosetting polymers. They cannot be softened again on heating
Eg: urea-formaldehyde resins, bakelite.

Polymers which are linear (slightly branched) long-chain polymers, which can be repeatedly softened and hardened on heating are called thermoplastic polymers. Hence, they can be modified again and again.                                                                                            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 ($CH_{2}=CHCl$)
(2) Tetrafluoroethylene ($CF_{2}= CF_{2}$)
(3) Formaldehyde (HCHO) and phenol ($C_{6}H_{5}OH$)

Q 13: Write the name and structure of one common initiator, which are used in free radical addition polymerisation.

Ans:

Benzoyl peroxide is one of the common initiator used in free radical addition polymerization.

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

Ans:
Natural rubber is a linear cis-polyisoprene in which the double bonds are present between
$C_{2}\;and\;C_{3}$ of the isoprene units.

Because of this cis-configuration, intermolecular interactions between the various strands
of isoprene are quite weak. As a result, various strands in natural rubber are arranged
randomly. Hence, it shows elasticity.
Q 15: Discuss the main purpose of vulcanization of rubber.

Ans:

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

Vulcanization is done mainly to improve the properties of natural rubber. In this process, a mixture of raw rubber with sulphur and appropriate additive is heated at a temperature range between 373 K and 415 K.

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

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

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

Q 18: Identify the monomer in the following polymeric structures.

(i)

(ii)

Ans:

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

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.

Q 20: What is a biodegradable polymer? Give an example of a biodegradable aliphatic polyester.

Ans:

A polymer, which can be decomposed by bacteria are called as Biodegradable polymer.  Poly – β – hydroxybutyrate – CO – β – hydroxyvalerate (PHBV) an example of a biodegradable aliphatic polyester.

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