CBSE Class 12 Chemistry Polymers Board Exam Notes

1 MARK QUESTIONS
Q.1 What does the designation 6,6 mean in the name nylon ‐6,6 ?
Ans. The acid and amine parts ,which condense to give the polymer both contain 6 carbons each .

Q.2 Give an example of elastomers .
Ans. Buna ‐S , Buna ‐N and neoprene are examples of elastomers .

Q.3 Name the polymers used in laminated sheets and give the name of monomeric units involved in its function .
Ans. Urea ‐ formaldehyde resins . Monomer units are Urea and formaldehyde .

Q.4 Explain the difference between Buna‐N and Buna‐S .
Ans. Both are copolymers . Buna‐N is a copolymer of 1,3 ‐butadiene and acrylonitrile while Buna‐S is a copolymers of 1,3‐butadiene and styrene .

Q.5 Why are rubbers called elastomers ?
Ans. Rubbers are stretched on application of force and regain its original state after the force is removed , therefore these are called elastomers .

ASSERTION - REASON TYPE
A statement of assertion is followed by a statement of reason. Mark the correct

choice from the options given below :
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Both assertion and reason are false.

1. Assertion : Strong interparticle forces exist in thermosetting polymers.
Reason : These polymers are heavily cross - linked. ( Ans - a)

2. Assertion : Most of the synthetic polymers are non - biodegradable.
Reason : During polymerisation, the polymers become toxic and non - biodegradable. ( Ans - c)

3. Assertion : Teflon is used for making oil seals, gaskets and non - stick surface coating.
Reason : Teflon is chemically inert and resistant to attack by corrosive reagents. (Ans - a)

4. Assertion : Low density polythene is used in the insulation of electricity carrying wires.
Reason : It is chemically inert, tough, flexible and poor conductor of electricity. ( Ans - a)
ONE - WORD ANSWER
1. What is the commercial name of polyacrylonitrile? ( Ans - orlon)
2. Name a polymer having a vinylic monomeric unit. (Ans - Polystyrene)

2 Marks Questions
Q1 Arrange the following polymers in increasing order of their intermolecular forces .
(i) Nylon 6 ,6 , Buna‐S , polythene .
(ii) Nylon 6, neoprene , polyvinyl chloride .
Ans. The increasing intermolecular forces of attraction follows the order : Elastomer, Thermo plastic, Fibre .
(i) Buna‐S , polythene , Nylon 6, 6 .
(ii) Neoprene , polyvinyl chloride , Nylon 6 .

Q.2 Distinguish between the terms homopolymers and copolymers and give an example of each.
Ans. Homopolymers :‐ Polymers whose repeating structural units are derived from only one type of monomer units are called h omopolymers . For example , Polythene , PVC, PAN , teflon , etc .
Copolymers :‐ Polymers whose repeating structural units are derived from different types of monomer molecules .

For examples , Buna‐S , nylon 6 ,6 , polyester , bakelite , etc .
Q.3 Differentiate the following pairs of polymers based on the property mentioned against each
(i) Novolac and bakelite ( structure)
(ii) Buna‐S and terylene ( intermolecular force of attraction )
Ans. (i) Novolac is a linear condensation polymer formed by reaction between phenol and formaldehyde . Bakelite is a cross linked condensation polymer formed by reaction between phenol and formaldehyde .
(ii) Buna‐S has weak intermolecular forces of attraction. terylene has stronger intermolecular force of attraction (dipole‐ dipole attraction ).

Q.4 Write the name of monomers used for getting the polymers PVC and PMMA . State one use for each of these polymers .
Ans. PVC:‐ Vinyl chloride is the monomer used in PVC . It is used for making pipes and electrical insulators .
PMMA:‐Polymethyl methacrylate is the monomer used in PMMA . It is used as substitute of glass .

Q.5 Write one difference between chain growth and step growth polymerisation . Give one example of each .
Ans. Chain growth polymerisation involves addition of monomers by free radical mechanism . Generally unsaturated monomers react by this mode of polymerisation to give polymers . Example Polythene ,
polypropene .
Step growth polymerisation involves repetitive condensation reaction between two bifunctional monomers.
Ex Terylene.

3 Marks questions
Q.1 How does the presence of double bonds in rubber molecules influence their structure and reactivity?
Ans. Natural rubber is cis‐ 1,4 ‐polyisoprene and is obtained by linear polymerisation of isoprene units. The cis‐configuration at double bonds does not allow the polymer chains to come closer for effective interactions and hence intermolecular forces are quite weak. As a result, natural rubber i.e, cis‐polyisoprene has a randomly coiled structure and hence shows elasticity.

Q.2 How is bakelite made and what is its major use ? Why I s bakelite a thermosetting polymer?
Ans. Bakelite is obtained by condensation reaction of phenol and formaldehyde. It is used in making electrical switches and switch boards. It is thermosetting polymer because on heating it undergoes extensive cross linking in the mould.

Q.3 Draw the structures of the monomers of the following polymers :
(i) Polythene    (ii) PVC       (iii) Teflon
Ans  (i) Polythene:‐ The structure of the monomer of polythene is :
CH2= CH2
(ii) PVC( polyvinylchloride) :‐ The structure of monomer of PVC is given below :
CH2=CH _ Cl
Teflon:‐The structure of the monomer of t eflon is : CF2=CF2

Q.4 (a) Give an example of synthetic rubber and mention i ts main advantages.
(b) Write the monomers of Dacron.
(c) Arrange the following polymers in increasing order of tensile strength : Nylon‐6 , Buna‐S , Polythene.

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