Bihar Board - Class 12 Chemistry - Chapter 15: Polymers Short Answer Question

                                        Short Question Answer

Question.1. What are polymers?

Answer: Polymers are high molecular mass substances (103-107 u) consisting of a very large number of simple repeating structural units joined together through covalent bonds in a linear fashion. They are also called macromolecules. Ex: polythene, nylon 6 , 6 , bakelite, rubber, etc.

Question.2. Explain the terms polymer and monomer.

Answer: 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. Polymers are also called macromolecules. Some examples are polythene, nylon-66, bakelite, rubber, etc. Monomers are the. simple and reactive molecules from which the polymers are prepared either by addition or condensation polymerisation. Some examples are ethene, vinyl chloride, acrylonitrile, phenol and formaldehyde etc.

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Question.3. Distinguish between the terms homopolymer and copolymer and give an example of each.
Answer: Polymers whose repeating structural units are derived from only one type of monomer units are called homopolymers, e.g., PVC polyethene, PAN, teflon, polystyrene, nylon-6 etc.
Polymers whose repeating structural units are derived from two or more types of monomer molecules are copolymers, e.g., Buna-S, Buna-N, nylon-66, polyester, bakelite.

Question.4. How do you explain the functionality of a monomer?
Answer: Functionality of a monomer implies the number of bonding sites present in it. For example, monomers like propene, styrene, acrylonitrile have functionality of one which means that they have one bonding site.
Monomers such as ethylene glycol, hexamethylenediamine, and adipic acid have functionality of two which means that they have two bonding sites.

Question.5. Define the term polymerisation?
Answer:  It is a process of formation of a high molecular Sol. mass polymer from one or more monomers by linking together a large number of repeating structural units through covalent bonds.

Question.6. Define thermoplastics and thermosetting polymers with two examples of each

Answer: Thermoplastics polymers are linear polymers which can be repeatedly melted and molded again and again on heating without any change in chemical composition and mechanical strength. Examples are polythene and polypropylene.

Thermosetting polymers, on the other hand, are permanently setting polymers. Once on heating in a mold, they get hardened and set, and then cannot be softened again. This hardening on heating is due to cross- linking between different polymeric chains to give a three dimensional network solid. Examples are bakelite, melamine-formaldehyde polymer etc.

Question.7. Are polyesters and polyacrylates the same ? Justify your answer.
Answer:
Polyesters and polyacrylates are different types of polymer and differ in following ways:

• Polyacrylates are homopolymer, while the polyesters are co-polymer in nature.

• The mode of synthesis of polyacrylates is addition polymerization, while those of polyester is condensation polymerization.

• Polymerization occurs across C=C bond in polyacrylates whereas, in polyesters it is through ester linkage.

Question.8.  What is meant by 'copolymerisation'?
Answer:
When two or more different monomers are allowed to polymerize together, the product formed is called a copolymer and the process is called copolymerisation. 

Question.9.  What are biodegradable polymers?
Answer:
Biodegradable polymers: All those biopolymers which disintegrate by themselves in biological systems during a certain period of time by enzymatic hydrolysis are called biodegradable polymers.
Example: Poly--Hydroxybutyrate-Co--Hydro- ky valerate (PHBV)
Uses: These are used 

1. in packaging 

2. in orthopedic devices 

3. in controlled drug release 

4. in bacterial degradation 

Question.10.  Define the term, 'homopolymerization' giving an example. 

Answer:

The polymer formed by the polymerization of single/same monomeric species is known as homopolymerization. 

Example: Polythene/PVC/Polypropene. 

Question.11.  How does a homopolymer differ from a copolymer? 

Answer:

Homopolymers: Polymers whose repeating structural units are derived from only one type of monomer units are called homopolymers. Example: Polyethene, PVC, teflon. 

Copolymers: Polymers whose repeating structural units are derived from two or more types of monomer molecules are copolymers. Example: Buna-S, Nylon 6, 6 .

Question.12. Draw the structures of the monomers of the following polymers: 

(i) Teflon 

(ii) Polyethene 

Answer:

(i) Teflon 

(ii) Polyethene

Question.13.  What is the repeating unit in the condensation polymer obtained by combining HO2CCH2CH2CO2H (succinic acid) and H2NCH2CH2NH2 (ethylene diamine)? 

Answer:

Question 14. Define thermoplastics and thermosetting polymers with two examples of each.
Answer:
Thermoplastics polymers are linear (slightly branched) long-chain polymers, which can be repeatedly softened and hardened on heating. Hence, they can be modified again and again. Examples include polyethylene, polystyrene.

Thermosetting polymers are cross-linked or heavily branded polymers that get hardened during the molding process. These plastics cannot be softened again on heating. Examples of thermosetting plastics include bakelite, urea-formaldehyde resins.

Question.15.  Mention two important uses of each of the following:
(i) Bakelite
(ii) Nylon-6
Answer:
(i) Bakelite: 

1. It is used in making handles of utensils. 

2. Also used in production of billiard balls, dominoes and pieces for games like chess. 

(ii) Nylon-6: 

1. Nylon is used in making stockings. 

2. It is also used for making parachutes. 

Question.16. In which classes, the polymers are classified on the basis of molecular forces?
Answer:
On the basis of the magnitude of intermolecular forces present in polymers, they are classified into the following groups:

• Elastomers

• Fibers

• Thermoplastic polymers

• Thermosetting polymers

Question.17. What is teflon ? Write its uses.

Answer:

It is a polymer obtained by the polymerization of tetrafluoroethylene in presence of benzoyl peroxide.

Uses: For making gasket, packing of pump, valve seal, bearing, etc.

Question.18.How does the presence of double bonds in rubber molecules influence their structure and reactivity?

Answer: From the structural point of view, the natural rubber is a linear cis- 1,4-polyisoprene. In this polymer, the double bonds are located between C2 and C3 of isoprene units. This cis-configuration about double bonds does not allow the chains to come closer for effective interactions and hence intermolecular forces are quite-weak. Therefore, natural rubber has a coiled structure and shows elasticity.

Question.19.  Write the names of the monomers of the following polymers:
(i) Polythene
(ii) Polyvinyl chloride
(iii) Bakelite
Answer:
(i) Polyethene

(ii) PVC (Polyvinyl chloride)

(iii) Bakelite → Phenol and formaldehyde → Condensation polymer 

Question.20. What is the basic difference between following pairs:

(a) Elastomers and fibres

(b) Thermosetting polymer & thermoplastic polymers.

Answer:(a)

(b)

Question. 21. 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 between C2 and C3 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.

Question.22. Arrange the following polymers in increasing order of their intermolecular forces.

(i) Nylon 6 , 6 ,Buna-S Polythene.

(ii) Nylon 6 Neoprene  , Polyvinyl chloride.

Answer :  Different types of polymers have different intermolecular forces of attraction. Elastomers or rubbers have the weakest while fibres have the strongest intermolecular forces of attraction. Plastics have intermediate intermolecular forces of attraction. Hence, the increasing order of the intermolecular forces of the given polymers is as follows:

(i) Buna -S < polythene < Nylon 6 , 6

(ii) Neoprene < polyvinyl chloride < Nylon 6

Question.23. How is dacron obtained from ethylene glycol and terephthalic acid?

Answer : 

Dacron is obtained by the polymerization of ethylene glycol and terephthalic acid.

Question.24. Is (NH-CHR-CO)n a homopolymer or copolymer?

Answer : 

It is a homopolymer because the repeating structural unit has only one type of monomer unit, i.e., NH2-CHR-COOH.

Question.25. Explain the term co-polymerization and give two examples.

Answer : 

When two or more different monomers unite together to polymerize, the result- product is called a copolymer and the process is termed copolymerization. Thus, a copolymer contains a large number of units of each monomer used in the same polymeric chain. For example, Buna-S and Buna-N whereas Buna-S is a copolymer of 1 , 3-butadiene and styrene while Buna-N is a copolymer of 1 , 3-butadiene and acrylonitrile.