Question

NCERT Solutions Class 12 Chemistry Chapter 15 Polymers is made in such a way that it provides one-step solutions to all the difficult concepts with ease. Our experts at Sarthaks suggest students go through our NCERT Solutions to score good marks in their exams.

Some of the important concepts discussed in our NCERT Solutions Class 12 are:

• Polymers – a polymer is a long chain of natural or synthetic substances that are made of very big molecules which are known as macromolecules. There are different simple chemical units which are known as monomers. Polymers possess a wide range of properties. Polymer is also part of many living beings in the form of proteins, cellulose, and nucleic acids. Polymers are formed when there are many different numbers of monomers working together. A polymer can also be formed with different types of monomers attached.
• Classification of Polymers – polymer has a very complex structure and behavior and there is also various application of polymer. The main types of polymer are:
  • Natural Polymers
  • Semi-synthetic Polymers:
  • Synthetic Polymers:
  • Linear Polymers
  • Branched-chain Polymers
  • Cross-linked Polymers
  • Classification Based on Polymerization
  • Classification Based on Monomers
  • Classification Based on Molecular Forces
• Types of Polymerisation Reactions – the process of formation of a polymer with the help of monomer molecules is called polymerization. There are two types of polymerization. The first one is called the chain reaction (addition) and the step-reaction (condensation) polymerization. The macromolecule of polymer forms large linear or branched chains. There is a polymer that is formed with the large molecules which have also formed with the monomers.
• Molecular Mass of Polymers – the molecular mass of any polymer is calculated by the sum of atomic weights of individual atoms which consist of the molecules.

NCERT Solutions Class 12 Chemistry is explained in-depth to provide solutions to difficult concepts.

Answer 1

NCERT Solutions Class 12 Chemistry Chapter 15 Polymers

1. Explain the terms polymer and monomer.

Answer:

Polymers can be defined as huge molecular mass macro-molecules made of repeating monomer-derived structural units. Polymers consists of a huge molecular mass of (10³ − 10⁷u). 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.

Examples of monomer: propene, ethene, vinyl chloride, styrene.

2. What are natural and synthetic polymers? Give two examples of each type.

Answer:

Polymers naturally found are known as Natural Polymers. 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).

3. Distinguish between the terms homopolymer and copolymer and give an example of each.

Answer:

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.

4. How do you explain the functionality of a monomer?

Answer:

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

For example, the functionality of monomers such as ethene and propene is one and that of 1, 3-butadiene and adipic acid is two.

5. Define the term polymerisation.

Answer:

Polymerization is the process of forming high molecular mass (10³ − 10⁷ u) macromolecules, which consist of repeating structural units derived from monomers. In a polymer, various monomer units are joined by strong covalent bonds.

6. Is \((- NH-CHR-CO - )_n\), a homopolymer or copolymer?

Answer:

\((- NH-CHR-CO - )_n\) is a homopolymer, the reason being that it is derived from a single monomer unit,

\(NH_2-CHR-COOH.\) 

7. Determine the groups where the polymers are graded according to molecular forces?

Answer:

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

8. How can you differentiate between addition and condensation polymerisation?

Answer:

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.

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.

9. Explain the term copolymerisation and give two examples.

Answer:

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. An example of copolymerization is the process of forming polymer Buna-S from 1, 3-butadiene and styrene.

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

10. Write the free radical mechanism for the polymerisation of ethene.

Answer:

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.

11. Define thermoplastics and thermosetting polymers with two examples of each.

Answer:

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.

12. Write the monomers used for getting the following polymers.

(i) Polyvinyl chloride 

(ii) Teflon 

(iii) Bakelite

Answer:

(1) Vinyl chloride (CH₂ = CHCl)

(2) Tetrafluoroethylene (CF₂ = CF₂)

(3) Phenol C₆​H₅​OH) and Formaldehyde (HCHO)

13. Write the name and structure of one of the common initiators used in free radical addition polymerisation.

Answer:

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

14. How does the presence of double bonds in rubber molecules influence their structure and reactivity?

Answer:

Natural rubber is a linear cis-polyisoprene consisting of double bonds between the two units of isoprene C₂​ and C₃​.

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.

Answer 2

15. Discuss the main purpose of vulcanisation of rubber.

Answer:

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 is easy 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.

16. What are the monomeric repeating units of Nylon-6 and Nylon-6,6?

Answer:

Nylon 6 monomeric repeat unit is [NH−(CH_2​)₅​−CO], derived from Caprolactam. 

The nylon 6, 6 monomeric repeat complex is 

[NH−(CH₂)​₆​−NH−CO−(CH₂​)_4​−CO], which is derived from diamine hexamethylene and adipic acid.

17. Write the names and structures of the monomers of the following polymers:

(i) Buna-S 

(ii) Buna-N 

(iii) Dacron 

(iv) Neoprene

Answer:

18. Identify the monomer in the following polymeric structures.

(i) 

(ii)

Answer:

(i) Hexamethylene diamine is the monomer of the given polymeric structure [H₂​N(CH₂​)6​NH₂​] and decanoic acid [HOOC−(CH₂)₈​−COOH].

(ii) The monomers of the given polymeric structure are

19. How is dacron obtained from ethylene glycol and terephthalic acid ?

Answer:

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

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

Answer:

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.