Introduction to NCERT Exemplar Solutions for Class 12 Chemistry Chapter 15: Polymers
Polymers are large molecules composed of repeating units called monomers, linked together by covalent bonds. They are widely used in everyday life and industry due to their versatility, durability, and range of properties. Chapter 15 of Class 12 Chemistry explores the classification, methods of preparation, properties, and applications of polymers. The NCERT Exemplar Solutions provide detailed explanations to conceptual and application-based problems, helping students understand polymer Chemistry in depth.
Introduction and Classification
Polymers are classified into three main types:
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Natural polymers: These occur in nature, such as proteins, nucleic acids, starch, and rubber.
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Synthetic polymers: Produced artificially, like nylon, polyethylene, polyvinyl chloride, and polystyrene.
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Biodegradable and non-biodegradable polymers: Biodegradable polymers, such as polylactic acid, break down naturally, while non-biodegradable ones persist in the environment.
Exemplar questions often ask students to classify polymers based on their origin, functionality, or environmental impact.
Methods of Polymerization
Polymers are formed through two main mechanisms:
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Addition polymerization (chain-growth polymerization): Monomers with double bonds, such as ethene or propene, react to form long chains without the loss of any atom. Examples include polyethylene and polypropylene.
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Condensation polymerization (step-growth polymerization): Monomers with two functional groups react to form polymers along with the elimination of small molecules like water or methanol. Examples include nylon, terylene, and bakelite.
Exemplar solutions explain stepwise mechanisms, showing how functional groups react and form repeating units. Questions often require writing structural formulas for polymers derived from given monomers.
Important Synthetic Polymers
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Nylon: A polyamide formed by condensation of diamine and dicarboxylic acid. It is used in textiles, ropes, and carpets.
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Terylene (Dacron): A polyester formed from diacid and diol. It is used in fabrics, bottles, and films.
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Bakelite: A thermosetting polymer used in electrical appliances and as a heat-resistant material.
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Polyethylene and polypropylene: Widely used in packaging, containers, and household products.
Exemplar questions often require students to identify monomers, write the polymerization reaction, and distinguish between thermoplastic and thermosetting polymers.
Properties of Polymers
Polymers exhibit a range of physical and chemical properties depending on their structure:
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Thermoplastics soften on heating and can be remolded, e.g., polyethylene.
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Thermosetting plastics harden on heating and cannot be reshaped, e.g., bakelite.
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Elasticity is seen in rubber and certain synthetic fibers.
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Solubility and resistance: Polymers are generally insoluble in water and resistant to chemicals, making them useful in harsh environments.
Exemplar solutions provide reasoning-based questions comparing properties of different polymers, reinforcing conceptual clarity.
Applications of Polymers
Polymers have extensive applications in daily life and industry:
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Textiles: Nylon, polyester, and acrylic fibers.
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Packaging: Polyethylene and polypropylene films and containers.
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Medicine: Polymers are used in prosthetics, sutures, and drug delivery systems.
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Engineering materials: Bakelite and other thermosetting polymers in electrical equipment and automotive components.
Exemplar questions often highlight real-world applications, encouraging students to connect theoretical concepts with practical usage.
Environmental Impact
Polymers, especially non-biodegradable ones, pose environmental challenges due to their persistence in nature. The chapter emphasizes recycling, development of biodegradable polymers, and responsible usage. Exemplar solutions include questions on environmental chemistry, guiding students to think critically about sustainable practices.