Polymer Chemistry Exercise Solutions | KalviGavani

Polymer Chemistry — Exercise Solutions Guide

Solve every exercise question on your own first, then compare your answers with the solutions below. Understanding the reasoning behind each answer is more important than memorising the final choice.

I. Multiple Choice Questions (MCQs)

Q1. The first man-made fibre is — (c) Rayon (obtained by chemically treating wood pulp)

Q2. Which is the strongest? — (b) Nylon (stronger than a steel wire of same thickness)

Q3. Natural fibre in a flame — (b) Burns (natural fibres burn; synthetic fibres melt)

Q4. Synthetic fibre similar to wool — (c) Acrylic (called artificial wool)

Q5. A good application of plastic — (a) Blood bags (safe, sterile, non-reactive)

Q6. A non-biodegradable material — (d) Wool (Note: debatable — wool is actually biodegradable; as per textbook key (d) is listed)

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Additional MCQs

II. Fill in the Blanks

1. Raincoat is an example of polyester fabric. 2. Resin codes are used to identify different types of plastics. 3. A polymer is a long chain made up of many repeated small units called monomers. 4. The fully natural fibre is called a plant fibre. 5. A natural fibre obtained by boiling cocoons is called silk.

Additional Fill in the Blanks

6. Polymers are long chains of repeating smaller molecules called monomers.

7. All proteins in your body are polymers. Proteins are made of amino acid monomers.

8. Cellulose is made of sugar molecules and is the main component of cotton.

9. Ethylene and propylene are building block monomers for many plastics.

10. Fibres are long strands of polymers interwoven into linear, string-like structures.

11. Fibres made from petroleum raw materials are synthetic fibres.

12. Cellulose dissolves in chemicals producing a syrup called viscose, which is then spun into rayon threads.

13. Nylon is made of chemical units called polyamides.

14. Spandex is a synthetic fibre that is strong and elastic.

15. Syringes are made from polypropylene — a lightweight, sterile thermoplastic.

16. The first plastic, created by Edmund Alexander Parkes, was called Parkesine.

17. Melamine resists fire and can tolerate heat.

18. PLA (Poly Lactic Acid) is a compostable and bioactive thermoplastic.

III. True or False

Additional True or False

IV. Match the Following

Additional Match

V. Arrange in Correct Sequence

1. Mix water, starch, vinegar, and glycerin in a cooking pot. 2. Continuously mix on medium heat until the liquid turns clear. 3. When the liquid begins to bubble, take it off the stove. 4. Spread the gel onto aluminium foil and allow it to cool. 5. Shape the material to form a cup or bowl. 6. Let the article cool for 24 hours before use.

Key idea: Starch = natural polymer, vinegar = cross-linking agent, glycerin = plasticiser for flexibility.

VI. Analogy

1. Cotton : natural :: Polyester : Synthetic Cotton is a natural fibre; polyester is made from chemicals.

2. PLA spoon : compostable :: Plastic spoon : Disposable PLA (Poly Lactic Acid) spoons break down naturally; regular plastic spoons are single-use but persist in the environment.

3. Nylon : melts on heating :: Silk : Burns on heating Synthetic nylon melts when heated; natural silk burns and chars.

VII. Assertion and Reason

Q1. A: Vegetable peels buried in soil disappear within two weeks. R: Vegetable peels are compostable. Answer: (a) Both A and R are true, and R correctly explains A.

Q2. A: Nylon takes very long to break down, but cotton decomposes in ~6 months. R: Nylon is non-biodegradable; cotton is biodegradable. Answer: (a) Both A and R are true, and R correctly explains A.

Q3. A: It is good to avoid plastics. R: Plastics end up polluting the environment. Answer: (a) Both A and R are true, and R correctly explains A.

VIII. Very Short Answers

Q1. What is the chemical name of the polymer in cotton? Cellulose. Cotton is composed of long chains of cellulose, a natural polymer of glucose.

Q2. What gives plastic different qualities? Different chemical additives. Additives change properties like flexibility, colour, UV resistance, and flame retardance.

Q3. Why is it not advisable to burn plastic and synthetic fabrics? Burning produces super-toxic chemicals that are difficult to store or dispose of safely, releasing harmful gases and dioxins.

Q4. Why doesn't a plastic bucket rust like iron? Plastic does not react with oxygen and humidity. Iron reacts with oxygen and moisture (rusting), but plastic is chemically inert.

Q5. Why is it better to avoid plastic products? Plastics do not decompose naturally and are often designed for single use, creating enormous waste that pollutes land and water.

Q6. Give two examples of thermosetting plastics. Bakelite and Melamine.

Q7. What is the 5R principle? Refuse, Reduce, Reuse, Recycle, and Recover — five strategies to manage plastic waste.

Additional Very Short Answers

Q8. What is the full form of PVC? Poly Vinyl Chloride.

Q9. Which synthetic fibre is like wool? Acrylic.

Q10. Why are plastics available in all shapes and sizes? Plastics are easily mouldable — they can be melted and poured into moulds of any shape.

Q11. What is the unit used in polymer formation? Monomer.

Q12. Which form of polyester replaces glass for bottles and jars? PET (Polyethylene Terephthalate).

Q13. What type of plastic is used for PVC pipes? Thermoplastic.

Q14. Which plastic is coated on firemen's uniforms? Melamine.

Q15. Name the natural polymer found in plants. Cellulose and Starch.

Q16. Why does burning wool smell like burning hair? Wool is made from sheep hair (a protein called keratin), so it smells similar to burning hair.

Q17. What is polymerisation? The process of linking monomers by covalent bonds to form polymers.

IX. Short Answers

Q1. What does biodegradable mean? A material that decomposes through natural processes and bacterial action. Examples include cotton, jute, paper, and food waste. Non-biodegradable materials like plastic do not decompose naturally.

Q2. What fabric is suitable for summer? Why? Cotton is the best fabric for summer. Synthetic fibres absorb very little moisture and do not allow air circulation, making them hot and uncomfortable. Cotton absorbs sweat, allows air to pass through, and keeps the body cool.

Q3. How do plastics impact animals and the environment? Plastics do not biodegrade, leading to waste accumulation and pollution in land and water. Animals confuse plastic for food and eat it, which can block their digestive system and cause death. Microplastics also enter the food chain.

Additional Short Answers

Q4. Why is rayon called artificial silk? Rayon has properties similar to silk — it is shiny, soft, and drapes well. It is obtained by chemical treatment of wood pulp, making it a semi-synthetic fibre that costs much less than natural silk.

Q5. What are the methods of disposing plastics? The 5R principle — Refuse, Reduce, Reuse, Recycle, and Recover. Refuse plastic when possible; reduce usage; reuse items; recycle what can be processed; and recover energy from non-recyclable plastic waste.

Q6. What is compostable plastic? Compostable plastic is derived from renewable resources like corn, sugarcane, avocado seeds, or shrimp cells. Microbes can break it down completely, leaving no toxic residue. PLA is an example.

Q7. Why do some animals eat plastic? Animals confuse plastic for food because of its shape, colour, or smell. Leftover food in plastic containers attracts animals by its scent, leading them to ingest the plastic along with the food.

Q8. What are microplastics? Microplastics are very small pieces of synthetic material from petrochemicals that persist in the environment. They break down from larger plastics but never fully decompose, polluting soil and water bodies.

Q9. Name household products that contain microbeads. Toothpaste, facewash, and body scrubs previously contained microbeads (tiny plastic particles). Many countries have now banned microbeads in these products.

Q10. Differentiate thermoplastics and thermosetting plastics. Thermoplastics soften on heating and can be bent and reshaped repeatedly (e.g., PVC, polythene). Thermosetting plastics, once moulded, cannot be softened by heating — they become hard and rigid permanently (e.g., Bakelite, melamine).

Q11. Why shouldn't hot food be kept in polythene containers? Polythene is a thermoplastic. Hot food can cause the container to deform or release harmful chemical substances into the food, posing health risks.

Q12. Why have plastics occupied our lives? Plastics are lightweight, strong, mouldable, flexible, waterproof, UV resistant, cheap, and convenient. These versatile properties make them hard to replace in daily use.

X. Detailed Answers

XI. Higher Order Thinking Skills (HOTS)

Q1. Why has the Tamil Nadu Government banned single-use plastics? Single-use plastics are the largest source of plastic pollution because they are designed to be used once and discarded. They do not biodegrade, accumulate in land and water bodies, harm wildlife, and clog drainage systems causing floods. The Tamil Nadu Government banned them to reduce these negative environmental consequences and encourage people to switch to sustainable alternatives.

Q2. A plastic bag in soil takes approximately 500 years to decompose. If a new generation starts every 30 years, how many generations would it take? Number of generations = 500 / 30 = 16.67, which means approximately 16 to 17 generations would pass before a single plastic bag fully decomposes. This highlights the extreme persistence of plastic in the environment.

Additional HOTS

Q3. Why did Ram choose nylon ropes for rock climbing? Nylon ropes are significantly stronger than natural fibre ropes. They are more elastic (absorb the shock of a fall), lighter in weight, and a nylon rope of the same thickness is stronger than a steel wire. These properties make nylon ropes the preferred choice for safety-critical activities like rock climbing.

Q4. Why did Ramya's mother advise her not to wear synthetic clothes in the kitchen? Why does Ramya like synthetic clothes? Synthetic fibres melt on heating. If they catch fire, the melted fabric sticks to the body and causes severe burns — this is why Ramya's mother advised against wearing them near a flame or in the kitchen. However, Ramya likes synthetic clothes because they dry quickly after washing, are durable, less expensive than natural fibres, readily available, and easy to maintain without wrinkling.

Common Mistakes to Avoid

1. Calling a single small molecule a polymer — A single unit is a monomer. Polymers are long chains of many monomers linked together.

2. Confusing thermoplastics and thermosetting plastics — Thermoplastics soften on reheating (PVC, polythene); thermosetting plastics do not (Bakelite, melamine). Electric switches are thermosetting, not thermoplastic.

3. Thinking all plastics are bad — Plastics have essential uses: blood bags, helmets, syringes, and fire-resistant coatings on firemen's uniforms.

4. Saying cotton is a synthetic fibre — Cotton is a natural fibre grown on plants. Only fibres made from chemicals (nylon, polyester, acrylic) are synthetic.

5. Confusing rayon with natural silk — Rayon is artificial silk made from wood pulp through chemical processing. Natural silk comes from silkworm cocoons.

6. Forgetting that nylon melts while natural fibres burn — Nylon melts and sticks to skin; natural fibres like cotton and silk burn and turn to ash.

7. Saying plastics dissolve in water — Plastics are insoluble in water. They resist water, which is actually one of their useful properties.

Exam Checklist

• [ ] Natural vs synthetic fibres — identify examples (cotton, jute, wool vs nylon, polyester, acrylic, rayon)
• [ ] Types of plastics — thermoplastic vs thermosetting (with examples)
• [ ] 5R principle — Refuse, Reduce, Reuse, Recycle, Recover
• [ ] Properties of rayon, nylon, polyester, and acrylic
• [ ] PET — full form (Polyethylene Terephthalate) and uses
• [ ] Biodegradable vs non-biodegradable materials
• [ ] Microplastics and their environmental impact
• [ ] Resin codes for plastic identification (1–7)
• [ ] Steps for making bioplastic (starch + vinegar + glycerin)
• [ ] Plastic-eating bacteria — Ideonella sakaiensis and PETase enzyme
• [ ] Advantages and disadvantages of synthetic fibres (table)
• [ ] Polymerisation — monomers linked by covalent bonds to form polymers
• [ ] Glass manufacturing — SiO2 heated with sodium carbonate, rapid cooling
• [ ] Cellulose as the natural polymer in cotton