NCERT Solutions for Class 12 Chemistry chapter 15 Polymers

Solutions to In-Text Questions Ex 15.1 to 15.6

Question 15.1 What are polymers?

Answer :

Polymers- Poly means many and mer means unit or parts. Polymers are high molecular masses macromolecules . These are formed by joining of the repeated units of monomers.

Question 15.3 (1) Write the names of monomers of the following polymers

Answer :

The given above polymer is Nylon6, 6
So, the monomer is adipic acid and hexamethylene diamine

Question 15.3 (2) Write the names of monomers of the following polymers

Answer :

It is a polymer of Nylon6 . So, the monomeric unit is Caprolactum.

Question 15.3 (3) Write the names of monomers of the following polymers

Answer :

the above polymer is a Teflon (PTFE)
the monomeric unit is tetrafluroethene

Question 15.4 Classify the following as addition and condensation polymers: Terylene, Bakelite, Polythene, Teflon.

Answer :

• Addition Polymers are formed by the direct addition of repeated monomers. Example- polyethene and Teflon
• Condensation polymers are formed by condensation of two or more than two monomers by eliminating by-product like water and HCl. Example- terylene and bakelite

Question 15.5 Explain the difference between Buna-N and Buna-S.

Answer :

Buna-N
It is a copolymer of 1,3-Butadiene and acrylonitrile. It is resistant to the action of petrol, lubricating oil and organic solvents. It is used in making oil seals and tank lining etc.

Buna-S
It is formed by copolymerisation of 1,3-Butadiene and Styrene. It is used for making automobiles tyres and rubber soles etc.

Question 15.6 Arrange the following polymers in increasing order of their intermolecular forces.
Nylon 6,6, Buna-S, Polythene

Answer :

Increasing order in their intermolecular forces-
Buna-S(elastomers)<Polyethene<Nylon6, 6(fibres

• (Thermoplastics, intermediate forces between elastomers and fibres)
• ( strong H-bond or dipole-dipole interaction)
• elastomers weakest force of attraction

NCERT Solutions for Class 12 Chemistry Chapter 15 Polymers- Exercise Questions

Question 15.1 Explain the terms polymer and monomer.

Answer :

Polymers- Poly means many and mer means unit or parts. Polymers are high molecular masses macromolecules. These are formed by joining of repeating unit of monomers.
Monomers- These are simple reactive units, which combine together to form large molecules through covalent bond.examples- ethene and hexamethylene diamine, adipic acid.

Question 15.2 What are natural and synthetic polymers? Give two examples of each type.

Answer :

Natural Polymers-
Polymers that formed naturally like formed by animals and plants. these are found in nature. Example- protein, starch, cellulose etc.

Synthetic Polymers-
Polymers made by human beings are called synthetic or man-made polymers. Examples- plastic(polyethene), nylon6,6 and nylon 6 etc.

Question 15.3 Distinguish between the terms homopolymer and copolymer and give an example of each.

Answer :

HOMO-POLYMER
These types of polymers are formed by polymerisation of one type of monomers.
examples - polyethene is the homopolymer of ethene monomers.

CO-POLYMER-
These types of polymers are formed by the polymerisation of two different monomers.
example- Nylon6, 6 is the copolymer of adipic acid and hexamethylene diamine.

Question 15.4 How do you explain the functionality of a monomer?

Answer :

The functionality of a monomer is the number of binding sites present in it. For example, for propene and ethene functionality is one but for adipic acid and 1,3- butadiene is two.

Question 15.5 Define the term polymerisation.

Answer :

The process of formation of polymers or high molecular masses from its respective monomers is known as polymerisation. In polymers monomers are held by cobalent bonds.

Question 15.6 Is , a homopolymer or copolymer?

Answer :

, is a homopolymer because it is obtained from a single monomer of

Question 15 . 7 Why do elastomers possess elastic properties?

Answer :

In elastomers, the polymeric chains are held by weak intermolecular forces of attraction. These weak binding forces allow them to stretch and a few cross-links are there in between the chains, which helps them to retract after stretching or releasing forces. Due to this elastomers are elastic in nature.
Example- Buna-S, Buna-N and Neoprene etc.

Question 15.8 How can you differentiate between addition and condensation polymerisation?

Answer :

Addition Polymerisation- The process of repeated addition of monomer, having a double or triple bond to form polymers. For example, polyethene is formed by the addition polymerisation of ethene.

Condensation Polymerisation- Process of formation of polymers by repeated condensation reaction between two different monomers, having bi-functionality or tri-functionality. A small molecule is eliminated like water and in each condensation step. For example Nylon 6, 6 is a condensation polymerisation of adipic acid and hexamethylene diamine.

Question 15.9 Explain the term copolymerisation and give two examples.

Answer :

The process of formation of polymers of two or more different monomeric units is known as copolymerisation. For example, Buna-S is formed by the copolymerisation.

Question 15.10 Write the free radical mechanism for the polymerisation of ethene.

Answer :

In free radical mechanism, there are three main steps-

1. Chain initiation
2. Chain propagation
3. Termination

1. Chain Initiation - the polymerisation of ethene to polythene consists of heating or exposing to light a mixture of ethene with a small amount of benzoyl peroxide initiator. Generating new and larger free radicals.

2. Chain Propagation Step - As the radical reacts with another molecule of ethene. So, another bigger sized radical is formed. The repetition of this step is chain propagation.

3. Chain Termination step - At some time the product radical reacts with another radical to form the polymerised product and this step is called the chain terminating step.

Question 15.11 Define thermoplastics and thermosetting polymers with two examples of each.

Answer :

Thermoplastic polymers are linear or slightly branched chained molecules. It can be repeatedly softened and hardened on heating. Thus they can be modified again and again. Examples- polyethene and polystyrene. These polymers have intermolecular forces of attraction intermediate between elastomers and fibres. Some examples of common thermoplastics are polyethene, polystyrene, polyvinyls, etc.

Thermosetting Plastics are cross-linked and heavily branched molecules, which get hardened during the moulding process. These polymers cannot be reused. For examples bakelite and urea-formaldehyde resin etc.

Question 15.12(i) Write the monomers used for getting the following polymers.
(i) Polyvinyl chloride

Answer :

For PVC (polyvinyl chloride) we use vinyl chloride as a monomer.

Question 15.12(ii) Write the monomers used for getting the following polymers.
(ii) Teflon

Answer :

The monomeric unit of Teflon (PTFE) is tetraflouroethene ( ). It is resistant to heat and chemical attack.

Question 15.12(iii) Write the monomers used for getting the following polymers.
Bakelite

Answer :

The monomeric unit of abkelite is phenol and formaldehyde.
(a) phenol-
(b) formaldehude-

Question 15.14 How does the presence of double bonds in rubber molecules influence their structure and reactivity?

Answer :

Natural rubber is a linear polymer of isoprene (2-methyl-1, 3-butadiene) and is also called as cis - 1, 4 polyisoprenes. Due to the cis configuration about the double bond, it is difficult to come closer for effective compactness due to the weak intermolecular attraction (van der Waals). Thus natural rubber has a coiled structure and it can be stretched like spring(show elastic nature).

Question 15.15 Discuss the main purpose of vulcanisation of rubber.

Answer :

The natural rubber has many flaws in following ways like-

• it becomes soft at high temperature and brittle at low temperature (<283K). And
• show very high water absorption capacity
• soluble in a non-polar solvent and
• poor resistant to the attack of oxidising agents.

To improve all these physical properties we do vulcanisation of rubber. During this process, sulphur cross-links are formed, which makes it hard, tough with high tensile strength.

Question 15.16 What are the monomeric repeating units of Nylon-6 and Nylon-6,6?

Answer :

The monomeric repeating unit of Nylon 6 is caprolactam and the monomers of Nylon6, 6 is adipic acid and hexamethylene diamine.

Question 15.17(i) Write the names and structures of the monomers of the following polymers:
Buna-S

Answer :

Name of monomer of Buna-S -(a) (1,3 butadiene)
(b) Styrene

Question 15.17(ii) Write the names and structures of the monomers of the following polymers:
Buna-N

Answer :

The momomeric unit of buna-N is

• 1, 3-Butadiene
• Acrylonitrile

The structure of the monomer are-

Question 15. 17(iii) Write the names and structures of the monomers of the following polymers:
Dacron

Answer :

The monomer of Dacron is-

-Ethylene glycol
-Terephthalic acid

Structures are-

Question 15.17(iv) Write the names and structures of the monomers of the following polymers:
(iv) Neoprene

Answer :

Monomer of Neoprene is Chloroprene.(2-chloro-1, 3-butadiene)
Structure-

Question 15. 18 (i) Identify the monomer in the following polymeric structures.

Answer :

It is Nylon10, 6
So, the monomer is Decanoic acid [ ]and hexamethylene diamine [ ]

Question 15.18 (ii) Identify the monomer in the following polymeric structures.

Answer :

The above polymer is melamine
So, the monomer is melamine and fomaldehyde( )

Question 15.19 How is dacron obtained from ethylene glycol and terephthalic acid ?

Answer :

Dacron(terelyne) is obtained from polymerisation of ethylene glycol and terepthalic acid at around 420 to 460 K. Also used in blending of cotton and wool fibres.

Question 15.20 What is a biodegradable polymer ? Give an example of a biodegradable aliphatic polyester.

Answer :

Polymers which are decomposed by bacteria are called bio-degradable polymers. Their degraded product does not cause any serious effect on the environment.
Bio-degradable aliphatic polyesters are -
1. poly -hydroxybutyrates-co- -hydroxy valerate(PHBV)
2. Nylon-2-Nylon-6