NCERT Solutions for Class 12 Science Chemistry Chapter 15 - Polymers

Answer:

Gycogen is a polymer of glucose that is stored by animals. It is found in liver, brain and muscles of animals. Cellulose is a polymer found in plant whereas amylose and amylopectin are structured units of starch. 

Hence, the correct answer is option (iv).

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Cellulose nitrate, Cellulose acetate and vulcanised rubeer are semisynthetic polymers made from cellulose, cellulose and natural rubber respectively. Cis-polyisoprene is not a semisynthetic polymer. It is another name of natural rubber which may be considered as a linear polymer of isoprene (2-methyl-1, 3-butadiene).

Hence, the correct answer is option (i).

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The commercial name of polyacrylnonitrile is orlon (acrilan).



Hence, the correct answer is option (ii).

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The example of biodegradable polymer is Poly $\beta$–hydroxybutyrate–co–$\beta$–hydroxy valerate because it undergoes bacterial degradation in the environment.



Hence, the correct answer is option (iii).
 

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Glyptal is synthesised by the polymerisation of ethylene glycol and phthalic acid with the elimination of water molecule.


Hence, the correct answer is option (i).

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Low density polythene has highly branched structure and is a poor conductor of electricity and tough but it is not hard.

Hence, the correct answer is option (ii).

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 can be obtained by addition polymerisation of  as shown below.


Hence, the correct answer is option (i).

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Nylon–6 is the polymer formed by polymerisation of given monomer unit of caprolactam.

Hence, the correct answer is option (iv).

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Polymers that need atleast one diene monomer for their preparation are Buna–S and neoprene.
Buna–S is prepared by copolymerisation of 1,3–butadiene and styrene.

Neoprene is prepared by polymerisation of chloroprene.


Hence, correct answers are options (ii) and (iii).
 

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Thermosetting polymers are heavily branched cross linked polymers that become infusible on moulding, which is why they cannot be reused. 

Hence, correct answers are options (i) and (iii).

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Teflon and Polystyrene are thermoplastic from the given options of polymer because:
(i) Thermoplastic polymers are linear or slightly branched long chain molecules.
(ii) These polymers are hard at room temperature, and they become soft on heating and again rigid on cooling. This process can be repeated as number of times as desired without any change in chemical composition.

Hence, the correct answers are option (i) and (iv).

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Nylon and terylene are used as fibre due to strong intermolecular forces like H-bonding which lead to close packing in chain resulting in crystalline nature.

Hence, correct answers are options (iii) and (iv).

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Repeated addition of a large number of same or different monomers possessing double or triple bonds leads to the formation of addition polymers. We get Orlon by addition polymerisation of acrylonitrile in presence of a peroxide catalyst.


We get Polystyrene by addition polymerisation of styrene.



Hence, correct answers are options (iii) and (iv).

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Bakelite and Melamine formaldehyde resin are condensation polymers.
Condensation polymers are formed by repeated condensation reaction between two bifunctional or trifunctional monomer units usually with elimination of small molecules like water, alcohol, ${\mathrm{CO}}_2, \mathrm{HCl}, {\mathrm{H}}_2\mathrm{O}.$

• Novalac is obtained by polymerisation of phenol and formaldehyde.

• Novolac, obtained on heating with formaldehyde, undergoes cross- linking to form an infusible solid mass called bakelite.

• Melamine– formaldehyde–resin

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The polymers which do not cause any harm to the environment and are easily decomposed are called biodegradable polymer.
PHBV can be formed by condensation polymerisation of 3-hydroxybutanoic acid and 3-hyrdoxypentanoic acid.


Glycine and amino caproic acid on polymerisation given Nylon–2–nylon 6 which is also biodegradable. 


Hence, correct answers are options (i) and (ii).

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Polychloroprene and Buna–N are the example of synthetic rubber.
A synthetic Polymer is a polymer that is not found in nature and can be synthesised in laboratory and industry.

• Polychloroprene is a polymer of chloroprene (monomer).

• Buna– N can be obtained by copolymerisation of 1,3–Butadiene and acyrlonitrile.

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Nylon and polysters can have strong intermolecular forces due to strong tensile strength and presence of either H–bonding or dipole–dipole interactions.

Hence, correct answers are option (i) and (iv).

Answer:

Apart from Nylon, Acrilan, Polystyrene, and teflon has vinylic monomer units as shown below.


Hence, correct answers are options (i), (ii) and (iv).

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Vulcanisation makes rubber more elastic and more stiff. On vulcanization sulphur forms cross links at the reactive sites of double bonds or at their reactive allylic position and thus rubber gets stiffened.

Hence, the correct answers are options (i) and (iv).

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The process consisting of heating a mixture of raw rubber with sulphur and an appropriate additive at a temperature range between 373 K to 415 K is called vulcanisation of rubber. The product is called vulcanised rubber. The probable structures of vulcanised rubber molecules are shown below.

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It is Homopolymer. A Homopolymer contains only one type of monomer units, to form a polymeric structure. Since the given figure is made up of only A type of monomer, it is a homopolymer.
 

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The given figure is of Copolymer. A copolymer contains more than one type of monomer units. Since, the given polymer is made up of A and B types of monomer, it is a copolymer.

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This is a type of chain growth polymerisation as there is no loss of small molecules like methanol, water etc.

The basic difference between chain growth and step-growth polymerisation is that:
In case of step-growth polymerisation, bifunctional or trifunctional monomers in the growing chains further react with each other to form longer chains.
In case of chain-growth polymerisation, to continue the growing chain, only monomers react with each other.

Answer:

The given figure is of cross-linked or network polymer.
A cross-linked polymer is formed when monomeric units are joined together by covalent bonds and secondary branches are formed in the structure. We can see secondary branches in between the main straight chains in the given figure. 

Hence, it is a cross-linked polymer.

Answer:

The given figure is formed by 1,4–addition of 2–methylbuta–1,3–diene (isoprene). The stereochemistry is 'Cis' throughout.
Hence, the given polymer is 'Cis'–polyisoprene i.e., natural rubber.

Answer:

Rubbers can change their shape on applying force and regain original state after the force is removed. They possess elastic properties. Therefore, rubbers are called elastomers.

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Enzymes act as biocatalysts in living organisms. And, they are mainly formed of proteins. Proteins are the polymers having monomeric units known as amino acids. Hence, an enzyme can be called a polymer.

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Yes, nucleic acid, protein and starch can be considered as step growth polymers because in their polymerisation reaction, they lead to removal of water molecule or any neutral molecule also.
Step growth polymers are formed by condensation polymerisation reaction resulting in the loss of simple molecule like water, alcohol that results in the formation of high molecular mass polymers. Nucleic acids, proteins and starch are formed in the same way. Hence, they can be considered as step-growth polymers.

Answer:

The given intermediate is formed by the condensation polymerisation of melamine and formaldehyde. Its polymerisation gives melamine formaldehyde.

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Cross-links are formed in the process of vulcanisation that is done to improve the physical properties of natural rubber.
By cross-linking, rubber gets hard and tough due to increased tensile strength. The vulcanised rubber has higher elasticity, more stiffness and it also has low water absorption tendency.

Answer:

Cis-polyisoprene posses the elastic property due to the existence of weak van der Waal's interactions. Due to the presence of these weak forces, the polymers becomes easily stretchable by applying force. They return to their original state when the force is removed. This is due to the elastic property. 

Answer:

HDP or High-Density Polymer consists of linear chains, and because of it molecules are closely packed in space. HDP, therefore has a higher density and melting point and is considered a translucent polymer.
It is more tougher, harder and has greater tensile strength than LDP.
We can use HDP in the manufacturing of containers like (buckets, mugs, tubs). or toys.
LDP or Low Density Polymer consists of branched structure and hence it does not pack well. Due to this, it has low density.
Low density polythene is chemically inert and tough but flexible and a poor conductor of electricity. Hence, it is used as an insulation for electrical wires and cables or as packaging material or in the manufacturing of toys, flexibles pipes etc.

Answer:

The role of benzoyl peroxide is to initiate the free radical polymerisation reaction. Taking an example of polymerisation of ethene to polyethene, let's understand it's role:
(i) Chain initiation - 

We can see from the above reaction, benzoyl peroxide initiates the polymerisation reaction by generating the free radicals. Therefore, it acts as a chain Initiator.

(ii) Chain Propagation -

We can see that the larger free radical generated in the chain initiation step further reacts with the second molecule of ethane to form another larger free radical.

(iii) Chain Termination -
For termination of the long chain, these free radicals can combine in different ways to form polythene. One mode of termination of chain is shown as under

Answer:

Polymers like Nylon have strong intermolecular forces like hydrogen bonding that leads to close packaging of the chains. Hence, this imparts crystalline nature to a polymer like nylon.

Answer:

We use, urea – formaldehyde resin for laminating sheets.
The monomeric units involved in its formation are urea (NH₂CONH₂) and formaldehyde (HCHO).

Answer:

We can see similarity in the structure of proteins and synthetic polyamides.
Polyamides like nylon is formed through an amide linkage by the combination of glycine and aminocaproic acid molecule.
We can see the similar amide linkage in protein as well when two amino acids join with each other. The peptide bond in protein is an amide linkage.
Thus, amide linkage is present in proteins and synthetic polyamides.

Answer:

The monomers used in addition polymerisation through radical pathway should be very pure because even a tiny amount of impurities may act as inhibitors which leads to the formation of polymers with shorter length. It can even slow down or stop the polymerisation.
 

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Answer:

(i) Nylon 6 - When we heat caprolactum with water at high temperature, Nylon 6 is formed.
(ii) PVC - It is the polymer of vinyl chloride.
(iii) Acrilan - Polyacrylonitrile is formed when addition polymerisation of acrylonitrile takes place in the presence of a peroxide catalyst.
(iv) Natural Rubber - Natural Rubber consists of a linear polymer of 2-Methyl–1,3–butadiene which is commonly known as isoprene. It is also called Cis-1,4–polyisoprene or simply Cis-polyisoprene.
​(v) LDP – LDP is known as Low-Density polythene.

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Column I	Column II
(i) Acrilan
(ii) Polystyrene
(iii) Neoprene
(iv) Novolac
(v) Buna – N

Answer:

Rayon is a semisynthetic polymer which is cellulose acetate and has superior properties than natural cotton. The strength of cellulose is enhances by acetylation which can be used for making packing material.

Hence, the correct answer is option (ii).

Answer:

Most of the synthetic polymers are not biodegradable because they are not easily broken by soil organisms and harmful to the environment. Polymerisation process does not induce toxic character in organic molecules.

Hence, the correct answer is option (iv).

Answer:

Olefinic monomers undergo addition polymerisation because in addition polymerisation, the molecules of the similar monomer or different monomers add together on a large scale to form a polymer. The monomers that are used are unsaturated compounds like alkenes, alkadienes and their derivatives. This mode of polymerisation increases the chain length. The chain growth takes place through the formation of free radicals or ionic species.
Polymerisation of vinylchloride is initiated by peroxides/persulphates.

Hence, the correct answer is option (i).

Answer:

Polyamides are best used as fibres because of high tensile strength. This is because of strong intermolecular forces (like hydrogen bonding within polyamides) lead to close packing of chains and increases the crystalline character, this provide high tensile strength to polymers.
 
Hence, the correct answer is option (ii).

Answer:

The monomer for natural rubber is isoprene molecule whereas neoprene is a synthetic rubber which is formed by polymerisation of chloroprene.

Hence, the correct answer is option (v).

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Network polymers are thermosetting because they are cross-linked or heavily branched molecules. They can't be reused once they undergo heating as after heating, it undergoes extensive cross linking in moulds and again become infusible. They have high molecular mass.

Hence, the correct answer is option (i).

Answer:

Polytetrafluoroethene or teflon is used in making non-stick cook-wares because it is chemically inert and is thermally stable. It has resistant to attack by corrosive reagents.
Fluorine is the element with highest electronegativity in the periodic table.

Hence, the correct answer is option (i)

Answer:

Synthetic polymers are quite resistant to environment oxidation and enzyme actions. Since, they do not easily degrade and cause the accumulation of solid waste. The new biodegradable synthetic polymers have been designed and developed which contains similar functional groups as present in biopolymers.
Biodegradable polymers are those polymers that can be degradable always.
For eg.- PHBV nylon-2, Nylon-6

Poly β-hydroxybutyrate − co-β-hydroxy valerate (PHBV)

• Obtained by the co-polymerisation of 3-hydroxybutanoic acid and 3-hydroxypentanioic acid

Answer:

Rubber is a natural polymer that possess elastic properties. In rubber, the polymer chain is held together by the weakest intermolecular forces ,i.e., van der Waals forces. These weak binding forces allows polymers to be stretched.



Plastics on the other side, are generally polymers of ethene known as polythene. They consists of linear or slightly branched long chain molecules that are capable of repeated softening on heating and hardening on cooling. The posses intermediate intermolecular forces of attraction. 

Answer:

Phenol and formaldehyde undergo condensation to give a polymer novolac (A) which on heating with formaldehyde undergoes cross-lnkge to give an infusible solid called Bakelite (B).
The sequence of reaction is written as follows:



The structural difference between both is that Novolac is a linear polymer whereas Bakelite is a cross linked polymer.

Answer:

Low density polythene and high density polythene are obtained under different conditions. They both differ in their structural features.
LDP is obtained by free radical reaction at high pressure and high temperature in the presence of traces of dioxygen or a peroxide initiator (catalyst). They are highly branched structures. It is flexible and a poor conductor of electricity.
High-density polythene, on the other hand, consists of closely packed linear molecular.
It is obtained by addition polymerisation of ethene in the presence of hydrocarbon solvent at low pressure and temperature upto 350 K in the pressure of catalyst called Ziegler-Natta catalyst. The polymer obtained under such conditions, is highly tough and has high density due to close packing.
Compared to LDP, HDP is harder and tougher.

Answer:

Polythene, polyvinyls and polystyrene soften on heating and harden on cooling. These polymers are called thermoplastic polymers.
Thermoplastic polymers are linear array of slightly branched long chain molecules.
These possess intermolecular forces whose strength lies between strength of intermolecular forces of elastomers and fibres.
On the other hand, Bakelite, urea-formaldehyde resin are thermosetting polymers. They undergo extensive cross linking in moulds and again become inflexible while heating.