2nd PUC Chemistry Question Bank Chapter 15 Polymers

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Karnataka 2nd PUC Chemistry Question Bank Chapter 15 Polymers

2nd PUC Chemistry Polymers NCERT Textbook Questions

Question 1.
Explain the terms polymer and monomer.
Answer:
A substance of a high molecular mass (10³ – 10⁷ u) formed by the combination of a large number of simple molecules called monomers by chemical bonds. The process by which monomers are converted into polymers is called polymerisation.
A monomer is a simple molecule capable of undergoing polymerisation and leading to the formation of the corresponding polymer e.g., Ethene, Vinyl chloride, etc.

Question 2.
What are natural and synthetic polymers? Give two examples of each type.
Answer:
1. Natural Polymers: The polymers which occur in nature mostly in plants and animals are called natural polymers. A few common examples are starch, cellulose, proteins, rubber nucleic acids, etc. Among them, starch and cellulose are the polymers of glucose molecules. Proteins are formed from amino acids which may be linked in different ways. These have been discussed in detail in unit 15 on biomolecules. Natural rubber is yet another useful polymer which is obtained from the latex of the rubber tree. The monomer units are of the unsaturated hydrocarbon 2-methyl-i, 3-butadiene, also called isoprene.
Examples of natural polymers: Natural rubber, cellulose, nucleic acids, proteins etc.

2. Synthetic polymers: The polymers which are prepared in the laboratory are called synthetic polymers. These are also called man-made polymers and have been developed in the present century to meet the ever-increasing demand of the modem civilisation.
Examples of synthetic polymers: Dacron (or terylene), Bakelite, PVC, Nylon-66, Nylon-6, etc.

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

Homopolymer	Copolymer
The polymers that are formed by the polymer­ization of a single monomer are known as a homopolymer. In other words, the repeating units of homopolymers are derived only from one monomer. For example, polythene is a homopolymer of ethane.	The polymers whose repeating units are derived from two types of monomers are known as copolymers. For example, Buna-S is a copolymer of 1, 3 – butadiene and styrene.

Question 4.
How do you explain the functionality of a monomer?
Answer:
Functionality means the number of binding sites in a molecule. For example, the functionality of ethene, propene, styrene, acrylonitrile is one while that of 1,3-butadiene, adipic acid, terephthalic acid, hexamethylenediamine is two.

Question 5.
Define the term polymerisation.
Answer:
Polymerization is the process of formation of a high molecular mass polymer from one or more types of monomers. Polymerization leads to the linkage together of several repeating structural units with covalent bonds.

Question 6.
Is ( NH-CHR-CO )₈, a homopolymer or copolymer?
Answer:
(NH CHR-CO)₈ is a homopolymer because it is obtained from a single monomer unit, NH₂-CHR-COOH.

Question 7.
In which classes, the polymers are classified on the basis of molecular forces?
Answer:
On the basis of molecular forces present between the chains of various polymers, these are classified as:

• Elastomers
• Fibres
• Thermoplastics
• Thermo setting plastics.

Question 8.
How can you differentiate between addition and condensation polymerization?
Answer:
Addition polymerisation is the process of repeated addition of monomers, possessing double or triple bonds to form polymers. For example, polythene is formed by additional polymerization of ethene

Condensation polymerization is the process Of the formation of polymers by repeated condensation reactions between two different bi-functional or tri-functional monomers. A small molecule such as water or hydrochloric acid is eliminated in each condensation. For example nylon 6, 6 is formed by condensation polymerisation of hexamethylene diamine and adipic acid.

Question 9.
Explain the term copolymerization and give two examples.
Answer:
The formation of polymers from two or more different monomeric units is called copolymerization. Multiple units of each monomer are present in a copolymer. The process of forming polymer BunaS from 1, 3-butadiene, and styrene is an example of copolymerization.

Nylon 6,6 is also a copolymer formed by hexamethylene diamine and adipic acid.

Question 10.
Write the free radical mechanism for the polymerisation of ethene.
Answer:
Polymerization of ethene to polythene consists of heating or exposing to a light mixture of ethene with a small amount of benzoyl peroxide as the initiator. The reaction involved in this process is given below:

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

Thermosetting plastics: These are normally semifluid substances with low molecular masses. When heated, they become
hard and infusible due to the cross-linking between the polymer chains. As a result, they also become three-dimensional in nature, They do not melt when heated. A few common thermosetting polymers are bakelite, inelamine-formaldehyde, urea-formaldehyde and polyurethane etc.
Examples of thermosetting polymers: polythene, polystyrene.

Thermoplastics: These are linear polymers and have weak van der Waals forces acting in the various chains and are
intermediate of the forces present in the elastomers and in the fibres. When heated, they melt and form a fluid which sets into
a hard mass on cooling, Thus, they can be cast into different shapes by using suitable moulds. A few common examples are
polyethylene and polystyrene polyvinyls etc. These can be used for making toys, buckets, telephone apparatus, television cabinets etc.
Examples of thermoplastic polymers: Bakelite, melamine-formaldehyde polymer.

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

1. Polyvinyl chloride
2. Teflon
3. Bakelite

Answer:

1. Vinyl chloride (CH₂ = CHCI)
2. Tetrafluro ethylene (CF₂ = CF₂)
3. Formaldehyde (HCHO) and phenol (C₆H₅OH)

Question 13.
Write the name and structure of one of the common initiators used in free radical addition polymerisation.
Answer:
One common initiator used in tree radical addition polymerization is benzoyl peroxide. Its structure is given below.

Question 14.
How does the presence of double bonds in rubber molecules influence their structure and reactivity?
Answer:
Natural rubber is a linear cis-polyisoprene in which the double bonds are present C₂ and C₃ of the isoprene units.

Because of this cis — configuration, intermolecular interactions between the various standard of isoprene are quite weak. As a result, various strands in natural rubber are arranged randomly. Hence it shows elasticity.

Question 15.
Discuss the main purpose of vulcanisation of rubber.
Answer:
Vulcanisation of Rubber: Rubber as such is used in the temperature range of 283 to 335 K. At higher temperatures, it becomes very soft and below this temperature, it tends to become brittle. To make it more useful, natural rubber is subjected to vulcanisation.

Vulcanised rubber has the following advantages over natural rubber:

• It makes rubber quite resistant to the action of organic acids.
• It makes rubber resistant to wear and tear.
• The elasticity of rubber increases and it remains so over a wide temperature range.
• It makes rubber resistant to the attack by air and oxygen.

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

• Nylon 6: e-amino caporic acid or 6-aminohexanoic acid.
• Nylon 66: Adipic acid and hexamethylenediamine.

Question 17.
Write the names and structures of the monomers of the following polymers:
(i) Buna-S
(ii) Buna-N
(iii) Dacron
(iv) Neoprene
Answer:

Question 18.
Identify the monomer in the following polymeric structures.

Answer:
Monomers are:

Question 19.
How is dacron obtained from ethylene glycol and terephthalic acid?
Answer:
The condensation polymerisation of ethylene glycol and terephthalic acid leads to the formation of dacron.

Question 20.
What is a biodegradable polymer? Give an example of a biodegradable aliphatic polyester.
Answer:
Nature has provided us a variety of polymers which can be produced by the biological systems in plants and animals. These are called biopolymers. Polysaccharides, proteins, and nucleic acids are common examples of biopolymers. In the biological system, these polymers decompose or hydrolyse in the presence of different enzymes. This means that they are biodegradable.
An example of aliphatic biodegradable polyester is PHBV i. e., Polyhydroxybutyrate-Co-p-hydroxy valerate.

2nd PUC Polymers Additional Questions

Question 1.
How are polymers classified on the basis of the solution?
Answer:

• Linear polymers such as high-density polythene (HDP), Polyvinylchloride, nylons, polyester etc.
• Branched polymers such as low-density polythene (LDP), amylopectin, glycogen etc.

Question 2.
What is the difference between Buna-S and Buna-N?
Answer:
Both are copolymers basically Buna-N is a copolymer of
1,3- butadiene and acrylonitrile. Buna-S is a copolymer of
1,3- butadiene and styrene.

Question 3.
What are the monomeric units of Nylon 6 and Nylon 6, 6?
Answer:
The monomeric repeating unit of Nylon 6 :

which is derived from caprolactam monomeric repeating unit of Nylon 6,6:

which is derived from 2 monomers, hexamethylenediamine, and adipic acid, and has the following structure.

Question 4.
What are the disadvantages of natural rubber which are compromised by vulcanisation?
Answer:

• It becomes more soft and sticky at high temperatures and brittle at low temperatures.
• It. has a large water absorption capacity and low tensile strength and low resistance to abrasion.
• Not resistant to the action of organic solvents.
• Easily attacked by oxygen and other oxidising agents.

Question 5.
What does PMMA stand for?
Answer:
Poly(methyl methacrylate)

Question 6.
How are polymers classified on the basis of molecular forces?
Answer:

• Elastomers
• Fibres
• Thermoplastic
• Thermosetting.

Question 7.
What is copolymerisation (and give an example)?
Answer:
When 2 or more different monomers are allowed to polymerise together, the product is called a copolymer and the process is called copolymerisation.
Ex: Buna-S: 1, 3 – butadiene and styrene.

Question 8.
What thermoplastic and thermosetting polymers?
Answer:
Thermoplastics are linear polymers which can be repeatedly softened on heating and hardened on cooling and hence can.be repeatedly used.
ex: polythene, polypropene, etc.

Thermosetting polymers are on the other hand permanently setting polymers. On heating, they harden and cant is softened again.
ex: bakelite, urea-formaldehyde resin.

Question 9.
What is the functionality of a polymer?
Answer:
It is the number of binding sites in a molecule.
The functionality of styrene is one, whereas it is for adipic acid.

Question 10.
Write a free radical mechanism for polymerisation of ethene.
Answer:
Initiation: