NCERT Solutions for Class 12 Chemistry Part 1 Chapter 15
Polymers Class 12
Chapter 15 Polymers Exercise Solutions
In text : Solutions of Questions on Page Number : 428
What are polymers?
How are polymers classified on the basis of structure?
Polymers are classified on the basis of structure as follows:
For e.g., high density polythene (HDP), polyvinyl chloride, etc.
For e.g., low density polythene (LDP), amylopectin, etc.
Classify the following as addition and condensation polymers: Terylene, Bakelite, Polyvinyl chloride, Polythene.
Addition polymers:
Polyvinyl chloride, polythene Condensation polymers: Terylene, bakelite
(i) Hexamethylenediamine and adipic acid
(iii) Tetrafluoroethene
Classify the following as addition and condensation polymers: Terylene, Bakelite, Polyvinyl chloride, Polythene.
Addition polymers:
Polyvinyl chloride, polythene Condensation polymers: Terylene, bakelite
Explain the difference between Buna-N and Buna-S.
Buna - N is a copolymer of 1, 3-butadiene and acrylonitrile. Buna - S is a copolymer of 1, 3-butadiene and styrene.
Arrange the following polymers in increasing order of their intermolecular forces.
(ii) Nylon 6, Neoprene, Polyvinyl chloride.
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)
Exercise : Solutions of Questions on Page Number : 437
Explain the terms polymer and monomer.
Polymers are high molecular mass macromolecules composed of repeating structural units derived from monomers. Polymers have a high molecular mass (103 - 107 u). In a polymer, various monomer units are joined by strong covalent bonds. Polymers can be natural as well as synthetic. Polythene, rubber, and nylon 6, 6 are examples of polymers.
What are natural and synthetic polymers? Give two examples of each type.
Natural polymers are polymers that are found in nature. They are formed by plants and animals. Examples include protein, cellulose, starch, etc.
Distinguish between the terms homopolymer and copolymer and give an example of each.
Homopolymer |
Copolymer |
The polymers that are formed by the polymerization of a single monomer are known as homopolymers. In other words, the repeating units of homopolymers are derived only from one monomer. For example, polythene is a homopolymer of ethene. |
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. |
Q4 :
Answer :
The functionality of a monomer is the number of binding sites that is/are present in that 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.
Define the term polymerisation.
Is , a homopolymer or copolymer?
In which classes, the polymers are classified on the basis of molecular forces?
On the basis of magnitude of intermolecular forces present in polymers, they are classified into the following groups:
(i) Elastomers
(ii) Fibres
(iii) Thermoplastic polymers
(iv)
How can you differentiate between addition and condensation polymerisation?
Explain the term copolymerisation and give two examples.
Write the free radical mechanism for the polymerisation of ethene.
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.
The reaction involved in this process is given below:
Define thermoplastics and thermosetting polymers with two examples of each.
Thermoplastic 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 polythene, polystyrene.
Write the monomers used for getting the following polymers.
Answer :
(i) Vinyl chloride (CH2=CHCl)
(ii) Tetrafluoroethylene (CF2 = CF2)
(iii)
Write the name and structure of one of the common initiators used in free radical addition polymerisation.
How does the presence of double bonds in rubber molecules influence their structure and reactivity?
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.
Discuss the main purpose of vulcanisation of rubber.
Natural rubber though useful has some problems associated with its use. These limitations are discussed below:
1. Natural rubber is quite soft and sticky at room temperature. At elevated temperatures (> 335 K), it becomes even softer. At low temperatures (< 283 K), it becomes brittle. Thus, to maintain its elasticity, natural rubber is generally used in the temperature range of 283 K-335 K.
2. It has the capacity to absorb large amounts of water.
3. It has low tensile strength and low resistance to abrasion.
4. It is soluble in non-polar solvents.
5. It is easily attacked by oxidizing agents.
What are the monomeric repeating units of Nylon-6 and Nylon-6, 6?
The monomeric repeating unit of nylon 6 is , which is derived from Caprolactam.
Write the names and structures of the monomers of the following polymers:
(iii) Dacron (iv) Neoprene
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Polymer |
Monomer |
Structure of monomer |
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i |
Buna-S |
1, 3-butadiene |
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Styrene |
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ii |
Buna-N |
1, 3-butadiene |
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Acrylonitrile |
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iii |
Neoprene |
Chloroprene |
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iv |
Dacron |
Ethylene glycol |
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Terephthalic acid |
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Q18 :
(ii)
(i) The monomers of the given polymeric structure are decanoic acid and hexamethylene diamine .
(ii)
How is dacron obtained from ethylene glycol and terephthalic acid?
What is a biodegradable polymer? Give an example of a biodegradable aliphatic polyester.
A polymer that can be decomposed by bacteria is called a biodegradable polymer.
Poly-β-hydroxybutyrate-CO-β- hydroxyvalerate (PHBV) is a biodegradable aliphatic polyester.