NEET Chemistry: Polymers – Practice Questions

I. Multiple Choice Questions (MCQs)

1. Question: Which of the following is a condensation polymer? a) Polythene b) PVC c) Nylon 6,6 d) Teflon

2. Question: Which of the following is a synthetic rubber? a) Natural rubber b) Isoprene c) Buna-N d) Gutta Percha

3. Question: The monomer of natural rubber is: a) Neoprene b) Isoprene c) Acrylonitrile d) Chloroprene

4. Question: The process of heating natural rubber with sulfur is called: a) Polymerization b) Vulcanization c) Esterification d) Condensation

5. Question: Which of the following is a thermoplastic polymer? a) Bakelite b) Melamine-formaldehyde resin c) Polythene d) Urea-formaldehyde resin

6. Question: Dacron is also known as: a) Orlon b) Terylene c) Acrilan d) Saran

7. Question: The monomers of Nylon 6,6 are: a) Caprolactam b) Hexamethylenediamine and Adipic acid c) Ethylene glycol and Terephthalic acid d) Phenol and Formaldehyde

8. Question: Which type of polymerization involves the elimination of small molecules? a) Addition polymerization b) Condensation polymerization c) Free radical polymerization d) Co-polymerization

9. Question: Which of the following is a biodegradable polymer? a) PVC b) PHBV c) Teflon d) Polypropene

10. Question: Ziegler-Natta catalyst is used in the preparation of: a) LDPE b) HDPE c) Teflon d) Nylon 6,6

11. Question: Which of the following is a cross-linked polymer? a) LDPE b) PVC c) Bakelite d) Nylon 6

12. Question: What is the repeating unit in PVC? a) −CH2​−CH2​− b) −CH2​−CHCl− c) −CF2​−CF2​− d) −CH2​−CH(CN)−

13. Question: Which of the following statements is true about thermosetting polymers? a) They can be re-molded on heating. b) They are linear or slightly branched. c) They become hard and infusible on heating. d) They have weak intermolecular forces.

14. Question: The monomer of Teflon is: a) Vinyl chloride b) Tetrafluoroethene c) Acrylonitrile d) Ethylene

15. Question: Buna-S is a copolymer of: a) 1,3-Butadiene and Acrylonitrile b) Isoprene and Styrene c) 1,3-Butadiene and Styrene d) Chloroprene and Isoprene

II. Assertion-Reason Type Questions

Directions: In the following questions, a statement of Assertion (A) is followed by a statement of Reason (R). Choose the correct option. a) Both A and R are true and R is the correct explanation of A. b) Both A and R are true but R is NOT the correct explanation of A. c) A is true but R is false. d) A is false but R is true.

16. Assertion (A): Bakelite is a thermosetting polymer. Reason (R): Thermosetting polymers become hard and infusible on heating and cannot be reused.

17. Assertion (A): Natural rubber is a linear polymer of isoprene. Reason (R): Natural rubber is cis-polyisoprene.

18. Assertion (A): HDPE has higher density and melting point than LDPE. Reason (R): HDPE has a more compact and linear structure due to Ziegler-Natta catalysis.

19. Assertion (A): Cellulose is a natural polymer. Reason (R): Cellulose is found in plants and is a polymer of α-D-glucose.

20. Assertion (A): Polymers have very high molecular masses. Reason (R): Polymers are formed by the repetition of a large number of monomer units.

III. Short Answer / Conceptual Questions

21. Question: Differentiate between homopolymers and copolymers with one example each.

22. Question: Give the full form and uses of PHBV.

23. Question: What are elastomers? Give two examples.

24. Question: Why are Bakelite and Melamine-formaldehyde polymers classified as thermosetting polymers?

25. Question: What is polydispersity index (PDI) and what does its value (PDI > 1 or PDI = 1) signify for synthetic and natural polymers?

Answers and Explanations

I. Multiple Choice Questions (MCQs) – Answers

1. Answer: c) Nylon 6,6 Explanation: Nylon 6,6 is formed by the condensation reaction between hexamethylenediamine and adipic acid with the elimination of water molecules. Polythene, PVC, and Teflon are addition polymers.

2. Answer: c) Buna-N Explanation: Buna-N (Acrylonitrile Butadiene Rubber) is a synthetic rubber. Natural rubber, Isoprene (monomer), and Gutta Percha (natural polymer, trans-polyisoprene) are natural.

3. Answer: b) Isoprene Explanation: Natural rubber is a polymer of isoprene (2-methyl-1,3-butadiene).

4. Answer: b) Vulcanization Explanation: Vulcanization is the process of heating natural rubber with sulfur to improve its physical properties like elasticity and tensile strength by forming cross-links.

5. Answer: c) Polythene Explanation: Thermoplastics can be softened on heating and re-molded. Polythene is an example of a thermoplastic. Bakelite, melamine-formaldehyde resin, and urea-formaldehyde resin are thermosetting polymers.

6. Answer: b) Terylene Explanation: Dacron is a polyester also commonly known as Terylene.

7. Answer: b) Hexamethylenediamine and Adipic acid Explanation: Nylon 6,6 is a condensation polymer formed from hexamethylenediamine and adipic acid.

8. Answer: b) Condensation polymerization Explanation: Condensation polymerization involves the elimination of small molecules (like water, alcohol, HCl) during the formation of the polymer from monomers. Addition polymerization does not involve such elimination.

9. Answer: b) PHBV Explanation: PHBV (Poly-β-hydroxybutyrate-co-β-hydroxyvalerate) is a well-known example of a biodegradable polymer. PVC, Teflon, and polypropene are non-biodegradable.

10. Answer: b) HDPE Explanation: Ziegler-Natta catalyst (e.g., TiCl4​ and (C2​H5​)3​Al) is used for the low-pressure polymerization of ethene to produce High Density Polythene (HDPE), which has a linear structure. LDPE uses free radical initiators.

11. Answer: c) Bakelite Explanation: Bakelite is a highly cross-linked, network polymer. LDPE and Nylon 6 are linear/branched, and PVC is linear.

12. Answer: b) −CH2​−CHCl− Explanation: PVC (Polyvinyl chloride) is formed from the monomer vinyl chloride (CH2​=CHCl). The repeating unit is −CH2​−CHCl−.

13. Answer: c) They become hard and infusible on heating. Explanation: Thermosetting polymers form extensive cross-links upon heating, making them rigid, infusible, and unable to be reshaped.

14. Answer: b) Tetrafluoroethene Explanation: Teflon (Polytetrafluoroethene) is formed from the monomer tetrafluoroethene (CF2​=CF2​).

15. Answer: c) 1,3-Butadiene and Styrene Explanation: Buna-S is a synthetic rubber which is a copolymer of 1,3-butadiene and styrene.

II. Assertion-Reason Type Questions – Answers

16. Answer: a) Both A and R are true and R is the correct explanation of A. Explanation: Bakelite is indeed a thermosetting polymer. The characteristic property of thermosetting polymers is that they undergo extensive cross-linking upon heating, becoming hard and infusible, and cannot be re-molded or reused.

17. Answer: b) Both A and R are true but R is NOT the correct explanation of A. Explanation: Natural rubber is a linear polymer of isoprene, and it specifically exists as cis-polyisoprene. However, being cis-polyisoprene explains its elasticity, not just its classification as a linear polymer of isoprene. The reason doesn’t directly explain why it’s a linear polymer of isoprene (which is simply its chemical composition and structure).

18. Answer: a) Both A and R are true and R is the correct explanation of A. Explanation: HDPE (High Density Polythene) has a linear and closely packed structure due to its preparation using Ziegler-Natta catalysts, which leads to higher density and melting point compared to LDPE (Low Density Polythene), which has a branched structure.

19. Answer: c) A is true but R is false. Explanation: Cellulose is a natural polymer found in plants. However, it is a polymer of β-D-glucose, not α-D-glucose (starch is a polymer of α-D-glucose).

20. Answer: a) Both A and R are true and R is the correct explanation of A. Explanation: Polymers are indeed macromolecules with very high molecular masses because they are formed by the repetitive linkage of a large number of small molecular units called monomers.

III. Short Answer / Conceptual Questions – Answers

21. Answer:

• Homopolymers: Polymers formed from only one type of monomeric unit.
  • Example: Polythene (formed from ethene monomers).
• Copolymers: Polymers formed from two or more different types of monomeric units that polymerize together.
  • Example: Buna-S (formed from 1,3-butadiene and styrene monomers).

22. Answer:

• Full Form: PHBV stands for Poly(β-hydroxybutyrate-co-β-hydroxyvalerate).
• Uses: It is a biodegradable polymer used in specialty packaging, orthopedic devices, controlled drug release, and in the production of disposable items due to its biocompatibility and biodegradability.

23. Answer:

• Elastomers are rubber-like polymers that possess elastic properties, meaning they can be stretched to several times their original length and return to their original shape when the stretching force is removed. This property is due to weak intermolecular forces holding the polymer chains together, allowing them to coil and uncoil.
• Examples: Natural rubber, Buna-S, Neoprene.

24. Answer: Bakelite and Melamine-formaldehyde polymers are classified as thermosetting polymers because they undergo extensive cross-linking (formation of strong covalent bonds between polymer chains) upon heating during their formation. Once formed and hardened, this cross-linked network structure makes them rigid, infusible, and insoluble. They cannot be softened, melted, or reshaped by further heating.

25. Answer:

• Polydispersity Index (PDI): PDI is a measure of the molecular mass distribution in a polymer sample. It is defined as the ratio of the weight average molecular mass (Mˉw​) to the number average molecular mass (Mˉn​).
  • PDI=Mˉn​Mˉw​​
• Significance:
  • For natural polymers, molecules are typically of uniform size, so their Mˉw​ and Mˉn​ are nearly equal, making their PDI = 1 (monodisperse).
  • For synthetic polymers, molecules usually have a range of different molecular masses due to variations in polymerization chain lengths. Therefore, their Mˉw​ is greater than Mˉn​, and their PDI > 1 (polydisperse). A higher PDI indicates a broader distribution of molecular masses.