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

BSEB > Class 12 > Important Questions > Chemistry Chapter 15: Polymers Long Answer Question

The long question answers for Chapter 15: Polymers of Class 12 Chemistry are provided here in English. These questions are based on the NCERT curriculum for Class 12. They are designed to help students develop a thorough understanding of the key concepts covered in the chapter. These long question answers will be useful not only for the Class 12 board exams but also for entrance exams like NEET. The questions and answers for Bihar Board Class 12 Chemistry, Chapter 15: Polymers, have been prepared by expert teachers at Vidyakul.

Long Question Answer

Question 1. What are natural polymers ? Explain some polymers with examples.
Answer :
Natural polymers:
Those polymers which are found in nature (generally in plants and animals) are called natural polymers. The followings are their example:

(a) Polysaccharides:
Starch and cellulose are important examples of polysaccharides. They are the polymers of glucose. Cellulose is the main structural material of plants. Plants store their food in the form of starch.

(b) Proteins:
Proteins are polymers of a-amino acids. They are the main constituents of animal cells. Natural silk, wool and leather are some examples.

(d) Natural rubber:
Natural rubber is prepared from latex which is obtained from rubber trees. It is a polymer of 2-methyl-1,3-butadiene (isoprene). It may be noted that polymers like polysaccharides, nucleic acids, proteins, etc. which control various life processes in plants and animals are also called biopolymers.

Question 2. On the basis of structure polymers are of how many types ? Explain.
Answer :
Classification based on structure:
This classification is based upon how the monomeric units are linked together. The polymers of this class are of three types:

(i) Linear polymers:
In this type of polymers, the monomer units are linked together to form long linear chains. These linear chains are placed one above the other and are closely packed in space. If A is the monomeric unit then a linear chain is formed as given in Fig.

Characteristics:
Due to close packed structure, they have high densities, high tensile strength and high melting point, e.g., polythene, nylon, polystyrene, etc.

(ii) Branched chain polymers:
In this type of polymers, the monomer units combine to form a long chain which is called the main chain. Many side chains are connected to the main chain. The side chains of different lengths constitute branches, e.g., A is the monomeric unit which forms a straight linear chain (main chain). Side chain of A is connected to the main chain as shown in Fig. They are not closely packed.

Characteristics:
Due to irregular packed structure, branched chain polymers have low densities, low tensile strength and low melting point, e.g., low density polythene, amylopectin, glycogen, etc.

(iii) Cross-linked polymers:
In these polymers, the monomer units combine to form a three-dimensional network.

Question.3. Write the method of preparation, properties and uses of Nylon-6,6.
Answer :
Preparation:
Nylon is a polymer containing amideNylon-6,6 is prepared by the polymerization of hexamethylenediamine and adipic acid. The meaning of 6,6 is that in the polymer chain both acid and diamine molecules contain 6,6 carbon atoms.

Properties:

Nylon threads possess high tensile strength.
They are hard.
They are elastic in nature.
Structure of nylon is like protein.

Uses:

It is used for coating of wire, cables and other electrical goods because PVC is a good insulator of electricity.
It is used for making plastic pipes, gramophone records, hand bags, raincoats, inflatable toys, etc.
For making vinyl flooring, shower, curtains, false ceiling, wall covering, doors and windows.
For making shoes, heels and foot wear.
For making sheets of tank-linkings, raincoats, lacquers, rods, tubes, packings, table cloths, light fittings, safety helmets, refrigeration components, trays, cycles, motorcycle mudguards, flexible articles such as toys, insulators, leather clothes, dolls, dipped goods such as protective gloves.
It is used in the manufacture of types of cords, fabrics and ropes.

Question.4. What is Zieglar – Natta catalyst ? Write its uses.
Answer :
Zieglar – Natta catalyst:
Mixture of titanium tetrachloride and aluminum compound in an inert solvent (hexane) is called Zieglar – Natta catalyst.

Uses:
(i) At low pressure and temperature polythene is formed from ethylene.

It is used for making toys, radio, TV cabinets.

(ii) At low temperature and pressure, propylene in presence of Zieglar – Natta catalyst for polypropylene

It is used for making bottles, pipes, and gramophone records.

Question.5. Differentiate between Nylon -6 and Nylon-6,6.
Answer :
Difference between Nylon-6 and Nylon-6,6 polymer:

Nylon-6:

This is prepared by the condensation of caprolactam molecules.
Caprolactam contains a chain of 6 atoms hence this polymer is nylon-6.
It is used in sheets, bristles for brushes. Crinkled nylon is also used in elastic hosiery.

Nylon-6,6:

This is obtained by the condensation of hexamethylenediamine and adipic acid monomers.
Adipic acid and hexamethylene di amine both the compounds contain a chain of 6 carbons hence the polymer is called nylon-6,6.
It is used in the manufacture of tyres, cords, fabrics and ropes.

Question.6. Describe the preparation, properties and uses of teflon.
Answer :
Teflon or Polytetrafluoroethylene (PTFE):
This is obtained by the polymer – ization of tetrafluoroethylene. Tetrafluoroethylene is heated under pressure in the presence of ammonium pero xo disulphate.

Properties:

It is hard, heat resistant and chemically inert. It melts at 330C. It is unaffected by concentrated acids (cone. HNO3, cone. H2SO4 , cone. HCl) and concentrated sodium hydroxide solution even at high temperature.
It is a bad conductor of electricity.

Uses:

It is used in making cans used to store concentrated acid, aqua regia etc.
It is used as a non sticky coating on utensils.

Question.7. How is bakelite prepared ? Write its uses also.
Answer :
Bakelite is cross – linked polymer. It is prepared by condensation of phenol and formaldehyde in presence of alkali.

Uses:
Soft bakelite formed due to less polymerization are used as binder in wooden items, in varnishes and liquors. Hard bakelite are formed by high degree of polymerization and are used for manufacture of electrical goods, comb, fountain pens, gramophone records, table tops like pharmica, etc.

Question.8. What is neoprene rubber? Write its uses.
Answer :
Neoprene is a thermoplastic polymer of 2-chloro -1,3- butadiene (Chloroprene).
Method of preparation: By polymerisation of chloroprene in presence of potassium persulphate.

Uses:

For making petrol delivery pipes.
For making conveyor belts used in coal mines.

Question.9. In a classroom discussion, Ramu said that bakelite on heating changes to a hard, infusible mass.

Is his statement correct?
What type of plastic is this?
What are the monomers used for the production of bakelite?
Can you convert a switch made from bakelite into a Formica tabletop? Comment.
How is the polymer bakelite different from the polymer PVC?

Answer :

Yes.
Thermosetting plastic.
Phenol and HCHO.
Bakelite is a thermosetting plastic having a three-dimensional network structure. Thermosetting plastic once shaped changes to a hard infusible mass that can’t be reshaped or restructured.
Bakelite is a thermosetting plastic and PVC is a thermoplastic.

Question.10. Identify the monomer in the following polymeric structures:

Answer :

(1) HOOC- (CH2)8-COOH and H2N-(CH2)6-NH2

Decanoic acid or sebacic Hexamethylene

Acid diamine

Question.11. Discuss the main purpose of the vulcanization of rubber.
Answer: 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 temperature (<283 K) it becomes brittle. Thus to maintain its elasticity, natural rubber is generally used in the temperature range of 283-335 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

6. Vulcanization of natural rubber is done to improve all these properties. In this process, a mixture of raw rubber with sulfur and appropriate additive is heated at a temperature range between 373 K and 415 K.

Question.12. How are polymers classified on the basis of structure?
Answer : On the basis of structure, polymers are classified into three types. These are linear chain polymers, branched chain polymers and crosslinked polymers.

1. Linear chain polymers: In this case, the monomer units are linked to one another to form long linear chains. These linear chains are placed one above the other and are closely packed in space. The close packing results in high densities, tensile strength and also high melting and boiling points. High density polyethene is a very common example of this type. Nylon, polyesters and PVC are also linear chain polymers.

2. Branched chain polymers: In this type of polymers, the monomer units are linked to form long chains which also have side chains or branched chains of different Lengths attached to them. As a result of branching, these polymers are not closely packed in space. They have low densities, low tensile strength as well as low melting and boiling points. Some common examples of such polymers are ; low density polyethene, amylopectin, starch, glycogen etc.

3. Cross: linked polymers. In these polymers, also called net—work polymers, the monomer units are linked together to form three dimensionaL net—work as shown in the figure. These are expected to be quite hard, rigid and brittle. Examples of cross linked polymers are bakelite, glyptal. melamine formaldehyde polymer etc.

Question.13. Explain the difference between Buna-N and Buna-S.
Answer : Both Buna-N and Buna-S are synthetic rubber and are co-polymers in nature. They differ in their constituents.
Buna-N: Constituents are : buta-1,3-diene and acrylonitrile.
Buna-S: Constituents are : buta-1,3-diene, and styrene. They condense in the presence of Na.

Buna -S: It is a co—polymer of 1,3-butadiene and styrene and is prepared by the polymerisation of these components in the
ratio of 3 :1 in the presence of sodium.

Buna-N (Nitrile rubber): h is a co-polymer of buta-1.3-diene and acrylonitrile. It is formed as follows:

Question.14. What are natural and synthetic polymers ? Give two examples of each.
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.
Example 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 modern civilisation.
Example of synthetic polymers: Dacron (or terylene), Bakelite, PVC, Nylon-66, Nylon-6 etc.

Question.15. In which classes, are the polymers classified on the basis of molecular forces?
Answer : Polymers are classified into four classes on the basis of molecular forces. These are:
elastomers, fibers, thermoplastic polymers and thermosetting polymers.

1. Elastomers: In these polymers, the intermolecular forces are the weakest. As a result, they can be readily stretched by applying small stress and regain their original shape when the stress is removed. The elasticity can be further increased by introducing some cross – links in the polymer chains. Natural rubber is the most popular example of elastomers. A few more examples are of: buna-S, buna-N and neoprene.

2. Fibers: Fibers represent a class of polymers which are thread-like and can be woven into fabrics in a number of ways. These are widely used for making clothes, nets, ropes, gauzes etc. Fibers possess high tensile strength because the chains possess strong intermolecular forces such as hydrogen bonding. These forces are also responsible for close packing of the chains. As a result, the fibers are crystalline in nature and have aJso sharp melting points. A few common polymers belonging to this class are nylon – 66, terylene and polyacrylonitrile etc.

3. 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 fibers. 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 molds. A few common examples are polyethene and polystyrene polyvinyls etc. These can be used for making toys, buckets, telephone apparatus, television cabinets etc.

4. 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, melamine-formaldehyde, urea-formaldehyde and polyurethane etc.

Question16. Difference between Thermoplastic polymer and Thermosetting polymer.
Answer :

Thermoplastic polymer	Thermosetting polymer
(i) These polymers have intermolecular forces of attraction between those of elastomers and fibres.	(i) These are semifluid substances with low molecular masses which when heated in a mold, undergo change in chemical composition to give a hard, infusible and insoluble mass.
(ii) These are linear or slightly branched chain polymers which are hard at room temperature and become soft and viscous on heating and again rigid on cooling.	(ii) These have extensive cross-linking between different polymers chains to give a three dimensional network solid on heating.
(iii) These can be melted again and again without any change. Example: PVC, polyethene	(iii) These can be heated only once when these are permanently set into a solid which cannot be remelted and reworked. Example: Bakelite, melamine

Question.17. Differentiate between condensation and addition polymerisations. Give one example each of the resulting polymers.
Answer :
Condensation polymerisation: In this, two or more bifunctional molecules undergo a series of independent con- densation reactions with the elimination of simple molecules like H2O , alcohol, NH3 , CO2 , HCl etc. to form a macromolecule.
Example: Formation of nylon 6 , 6

Addition polymerisation: In this, the molecules of the same or different monomers simply add on one another to form macromolecules. These molecules occur among molecules containing double and triple bonds.
Example: Formation of polyethene

Question 18. Write the names and structures of monomers used for getting the following polymers.
(i) Buna-S
(ii) Nylon-6 ,6
Answer :
(i) Buna-S:

(ii) Nylon-6 ,6: It has two repeating monomers
(a) Hexa methylene diamine

(b) Adipic acid

Question.19. Give one example each of
(i) addition polymers
(ii) condensation polymers
(iii) copolymers.
Answer: (i) Addition polymers

(ii) Condensation polymers

(iii) Copolymers

Question.20. Explain the term co-polymerization and give two examples of copolymers and the reactions for their preparations.

Answer:

Co-polymerization : Co-polymerization is a polymerization reaction in which a mixture of more than one monomeric species is allowed to polymerise and form a co- polymer.

Example: Buna-S, Buna-N .

Equations:

Question.21.
(a) Differentiate between chain growth and step growth polymerization.
(b) What is the function of sulfur in the vulcanization of rubber?
Answer:
(a) Chain growth polymerization involves successive addition of monomer units to the growing chain carrying a reactive intermediate such as a free radical, a carbocation or a carbanion.

Example: Polyethene, Teflon, PAN etc.

In step growth or condensation polymerization, the polymer is formed in a stepwise manner with the loss of simple molecules like H2O , alcohol etc.

Example: Polyamides like Nylon 6 ,6 Polyesters etc.

(b) Sulphur introduces sulfur bridges or crosslinks between polymer chains thereby impartins more tensile strength, elasticity and resistance to abrasion.

Question.22. Write the names and structures of the monomers of the following polymers:
(i) Terylene
(ii) Buna-S
(iii) Neoprene
Answer:
(i) Terylene:
Terephthalic acid and ethylene glycol

(ii) Buna-S:

(iii) Neoprene: Monomer is 2-chloro-1,3-butadiene

Question.23. Explain the term 'copolymerization' and give two examples of copolymerization.
Answer:
When two or more different monomers are allowed to polymerize together, the product formed is called a copolymer and the process is called copolymerization.

Co-polymerization is a polymerization reaction in which a mixture of more than one monomeric species is allowed to polymerize and form a copolymer. e.g. Buna-S, Buna-N.
Equations:

Question.24. What is polymerization? Define and explain e terms: addition polymerization, condensation polymerization and copolymerization. Give one example each type.
Answer:
Polymers can also be classified on the basis of mode of polymerization into two sub groups:
(1) Addition polymers and
(2) Condensation polymers.

(1) Addition Polymers: The addition polymers are formed by the repeated addition of monomer molecules possessing double or triple bonds and the process by which addition polymers are formed is called addition polymerization.
for example:

(2) Condensation polymers: The condensation polymers are formed by repeated condensation reactions between two different bifunctional or trifunctional monomeric units and the process by which the condensation polymers are formed is called condensation polymerization. In these polymerization reactions, the elimination of small molecules such as water, alcohol, hydrogen chloride etc. take place. For example, nylon 6,6 is obtained by condensation polymerization of two monomers i.eHexamethylenediamine and adipic acid, each containing two functional groups with the loss of water molecule.
example:

Question.25. Explain how 1 ,3-butadiene polymerizes different routes.
Answer:
Butadiene is a conjugated diene and its free polymerization can occur in following two ways:
(i) When the polymerisation takes place at C1 and of butadiene, an unbranched polymer is formed. It can be either as a mixture of both polymers.