🧪 Chemistry · Topic 8 of 10
Start with the study notes on Synthetic Fibres & Plastics (definitions, examples and a quick revision), then work through 60 practice questions, each with the correct answer and a clear explanation of why it is right. When you are ready, take this topic as an interactive quiz to test yourself.
Topic overview
A polymer is a very large molecule made by joining many small units, called monomers, into a long chain. The word means “many parts”.
Examples:
Rayon is made by chemically treating wood pulp. It looks and feels like silk but is much cheaper. Because its raw material is natural, it is called semi-synthetic.
Example: Bed sheets, carpets (mixed with wool) and medical dressings.
Nylon, made in 1931, was the first fully synthetic fibre, prepared from coal, water and air. It is strong, elastic and light, and dries quickly.
Example: Parachutes, climbing ropes, seat belts, fishing nets, socks, tents and toothbrush bristles.
Polyester is made of repeating units called esters. It does not wrinkle easily, stays crisp and is easy to wash. Terylene and PET are types of polyester.
Example: Shirts and dress material; PET bottles and food jars.
Acrylic looks and feels like wool but is cheaper, lasts longer and comes in many colours.
Example: Sweaters, shawls and blankets.
Fibres are often mixed to combine their good points:
Example: In a burning test, nylon melts into a hard bead, cotton burns to soft ash, and wool smells like burning hair.
Plastics are polymers that can be moulded into almost any shape. There are two kinds:
Can be softened by heating and reshaped again and again.
Example: Polythene (bags, bottles) and PVC (pipes, cable covers, raincoats).
Once set, they cannot be softened again by heating.
Examples:
A biodegradable material is broken down naturally by bacteria, e.g. vegetable peels, paper and cotton. Plastics are non-biodegradable: they stay in the environment for hundreds of years.
Reduce · Reuse · Recycle · Recover
Examples:
| Misconception | Correct understanding |
|---|---|
| Rayon is a natural fibre. | Rayon is made from natural wood pulp, but by a chemical process, so it is semi-synthetic. |
| All plastics melt when heated. | Thermosetting plastics such as bakelite do not soften again. |
| Synthetic clothes are best for hot weather. | They don't absorb sweat; cotton is more comfortable. |
| Plastics rot away in a few months. | They are non-biodegradable and last for hundreds of years. |
| Burning plastic is a clean way to get rid of it. | It releases poisonous gases. |
What is a polymer?
A large molecule made by joining many small units (monomers).
Why is rayon called artificial silk?
It looks and feels like silk but is made from wood pulp.
Why is nylon used for parachutes?
It is very strong, elastic and light.
Why are synthetic clothes unsafe in a kitchen?
They melt and stick to the skin if they catch fire.
What is the difference between a thermoplastic and a thermosetting plastic?
A thermoplastic can be softened again by heat; a thermosetting plastic cannot.
Why is bakelite used for electric switches?
It is a poor conductor of heat and electricity.
Why are plastics harmful to the environment?
They are non-biodegradable, so they build up in soil and water for centuries.
What are the 4 R's?
Reduce, Reuse, Recycle and Recover.
Key takeaway: Synthetic fibres and plastics are useful, cheap polymers, but nature cannot break them down, so we must reduce, reuse and recycle them.
Notes written by Velnov for Class 6–8 students, following the topics of the NCERT science syllabus.
Q1. easy
Fibres made by human beings from chemicals are called:
Answer: A — Synthetic fibres
Synthetic (man-made) fibres such as nylon, polyester, rayon and acrylic are produced from chemicals, mostly petrochemicals. Cotton, wool, silk and jute are natural.
Q2. easy
Which of these is a NATURAL fibre?
Answer: A — Cotton
Cotton comes from the cotton plant, wool from sheep, silk from silkworms and jute from the jute plant. Nylon, polyester and acrylic are synthetic.
Q3. medium
A synthetic fibre is made of many small units joined together. Each small unit is called a:
Answer: A — Monomer
Monomers are the repeating small molecules. When many join into a long chain, the result is a polymer - the basic structure of all synthetic fibres and plastics.
Q4. medium
A large molecule made by joining many small repeating units is called a:
Answer: A — Polymer
The word polymer comes from Greek: poly means many and mer means part. Cellulose in cotton is a natural polymer; nylon and polyester are synthetic polymers.
Q6. medium
Rayon is called ARTIFICIAL SILK because it:
Answer: A — Is made from natural wood pulp but resembles silk in appearance
Rayon is obtained by chemically treating wood pulp. Because it has a silk-like lustre and feel but is far cheaper, it is called artificial silk.
Q8. medium
Rayon is commonly used to make:
Answer: A — Bed sheets, carpets and surgical dressings, and is mixed with cotton or wool
Rayon can be dyed in many colours and blended with cotton for bed sheets or with wool for carpets. It is also used in medical dressings.
Q10. medium
Nylon was prepared from:
Answer: A — Coal, water and air
Nylon is a truly synthetic fibre - the first one made entirely from chemicals derived from coal, water and air, with no plant or animal source.
Q11. medium
Which property makes nylon suitable for parachutes and ropes for rock climbing?
Answer: A — It is very strong, elastic and light
Nylon is strong, elastic and lightweight, and dries quickly. A nylon thread is actually stronger than a steel wire of the same thickness.
Q13. medium
Polyester is made of repeating units of:
Answer: A — An ester
Polyester means many esters. Esters are the chemicals that give fruits their pleasant smell, and joining many of them produces the polyester fibre.
Q15. medium
PET, used to make bottles, jars and films, is a familiar form of:
Answer: A — Polyester
PET (polyethylene terephthalate) is a polyester. It is widely used for soft drink bottles, food containers, utensils and wires because it is strong and transparent.
Q17. medium
Terrycot is a fabric made by mixing:
Answer: A — Terylene and cotton
Blended fabrics combine the best of both fibres. Terrycot mixes terylene with cotton, and terrywool mixes terylene with wool, giving strength plus comfort.
Q19. medium
Acrylic is a synthetic fibre that resembles:
Answer: A — Wool
Acrylic is often called artificial wool. It is cheaper than natural wool, available in many colours, and used for sweaters, shawls and blankets.
Q21. medium
Which is a key ADVANTAGE of synthetic fibres over natural fibres?
Answer: A — They dry quickly, are durable, less expensive and easily available
Synthetic fibres are strong, cheap, easy to maintain and readily available. Their main drawbacks are poor sweat absorption and non-biodegradability.
Q24. medium
Plastics are:
Answer: A — Polymers that can be moulded into different shapes
Like synthetic fibres, plastics are polymers. Their units may be arranged in a straight line or in a cross-linked pattern, which determines how they behave on heating.
Q27. medium
Which of these is a THERMOPLASTIC?
Answer: A — Polythene
Polythene and PVC are thermoplastics used for bags, bottles, toys and combs. Bakelite and melamine are thermosetting.
Q29. medium
Melamine is used to make floor tiles, kitchenware and fire-resistant fabrics because it:
Answer: A — Resists fire and can tolerate heat better than other plastics
Melamine is a thermosetting plastic that resists heat and fire. Uniforms of firefighters are coated with melamine to make them flame-resistant.
Q31. medium
Teflon, used as a non-stick coating on cookware, is special because it:
Answer: A — Is oil and water repellent and withstands high temperatures
Teflon is a special plastic on which oil and water do not stick, and it stands up to cooking temperatures - which is why non-stick pans are coated with it.
Q33. medium
Which property of plastics makes them useful for making raincoats and water tanks?
Answer: A — They are waterproof and do not corrode
Plastics do not absorb water or rust, so they are ideal for raincoats, buckets, pipes and storage tanks - unlike metal, which corrodes.
Q35. medium
Plastics are a serious environmental problem mainly because they are:
Answer: A — Non-biodegradable and persist in the environment for hundreds of years
Micro-organisms cannot break plastics down, so discarded plastic accumulates in soil, rivers and oceans, clogging drains and harming wildlife for centuries.
Q37. medium
Polythene bags thrown carelessly are dangerous to cattle because:
Answer: A — Animals swallow them along with food and the bags choke their digestive systems
Stray cattle eat food waste wrapped in polythene. The plastic collects in their stomachs, blocking digestion and often killing them.
Q39. medium
Which is the BEST first step in dealing with the plastic problem?
Answer: A — Reduce the use of plastics, for example by carrying a cloth bag when shopping
Reducing use tackles the problem at the source. Carrying jute or cotton bags avoids the need for plastic bags in the first place.
Q41. medium
Which of these should be used INSTEAD of plastic bags?
Answer: A — Jute or cotton bags
Jute and cotton bags are biodegradable, reusable and strong. Using them for shopping cuts plastic waste substantially.
Q43. medium
Plastics are preferred over metals for many uses because they are:
Answer: A — Light, cheap, strong for their weight, and easy to handle
Compared with metal, plastic is lighter, cheaper, does not corrode and can be moulded into any shape - which is why it has replaced metal in so many products.
Q45. medium
Micro-organisms cannot decompose plastics because plastics:
Answer: A — Have long, strong chains that bacteria have no enzymes to break
Bacteria evolved enzymes for natural materials, not for man-made polymers. Their strong carbon chains resist biological attack for hundreds of years.
Q47. medium
Synthetic fibres are made from raw materials obtained from:
Answer: A — Petrochemicals (petroleum products)
Nylon, polyester and acrylic are all made from petrochemicals, which is why the synthetic fibre industry is linked to petroleum refining.
Q49. medium
Why are synthetic fibres used in seat belts and parachutes?
Answer: A — They have very high tensile strength and do not tear easily
Nylon and similar fibres can withstand large forces without breaking, while remaining light and flexible - exactly what safety equipment needs.
Q51. medium
Which of these clothes would be BEST for a firefighter?
Answer: A — Cotton coated with melamine (fire-resistant)
Synthetic fibres melt and stick to skin. Melamine-coated cotton resists fire and does not melt, making it far safer for firefighting uniforms.
Q53. medium
A jute bag is preferred over a plastic bag mainly because jute is:
Answer: A — Biodegradable and made from a renewable plant
Jute is grown from a plant, decomposes naturally after use, and can be reused many times - so it does not accumulate in the environment.
Q55. medium
Which fibre would keep you MOST comfortable on a hot summer day?
Answer: A — Cotton
Cotton absorbs sweat and allows it to evaporate, cooling the body. Synthetic fibres trap sweat against the skin and feel uncomfortable in heat.
Q57. medium
Which overall statement about synthetic fibres and plastics is CORRECT?
Answer: A — Both are polymers made from petrochemicals - useful and cheap, but non-biodegradable, so they must be used and disposed of carefully
This sums up the topic: rayon, nylon, polyester and acrylic are synthetic fibres; polythene, PVC, bakelite, melamine and teflon are plastics; all are polymers whose greatest drawback is that nature cannot break them down.
Q58. medium
Why do plastic buckets last longer than metal ones?
Answer: A — Plastic does not rust or corrode when exposed to water
Metal buckets rust when they stay wet, weakening and eventually leaking. Plastic does not react with water or air, so it survives daily use for years.
Q60. medium
Fishing nets made of nylon are a problem when abandoned in the sea because they:
Answer: A — Do not decompose and keep trapping fish and other marine animals for years
Nylon is non-biodegradable and very strong. Lost or discarded nets, called ghost nets, drift for decades entangling turtles, dolphins and fish - a serious form of plastic pollution.
Q5. hard
Which natural fibre is itself a polymer, made of repeating glucose units?
Answer: A — Cotton (cellulose)
Cotton is cellulose, a natural polymer of glucose. This shows polymers occur in nature too - synthetic polymers simply copy the idea using chemicals.
Q7. hard
Rayon is different from other synthetic fibres because it is:
Answer: A — Obtained from a natural source (wood pulp) though prepared by a chemical process
Rayon is described as a regenerated or semi-synthetic fibre: the raw material is natural cellulose, but chemical processing gives it new properties.
Q9. hard
Nylon was the FIRST fully synthetic fibre, prepared in:
Answer: A — 1931
Nylon was made in 1931 without using any natural raw material - it was prepared entirely from coal, water and air.
Q12. hard
Which of these is a common use of nylon?
Answer: A — Socks, ropes, tents, toothbrush bristles, parachutes and seat belts
Nylon's strength, elasticity and resistance to wear make it useful in fishing nets, ropes, car seat belts, curtains, sleeping bags and brush bristles.
Q14. hard
Which property makes polyester ideal for making dress material?
Answer: A — It does not get wrinkled easily and stays crisp
Polyester resists wrinkling, dries quickly and is easy to wash. Terylene, a well-known polyester, can be drawn into very fine yet strong fibres.
Q16. hard
Terylene is a well-known example of:
Answer: A — Polyester
Terylene is a popular polyester fibre that can be drawn into very fine but strong fibres, often blended with cotton or wool for clothing.
Q18. hard
Polycot is a blend of:
Answer: A — Polyester and cotton
Polycot combines the wrinkle resistance and strength of polyester with the softness and absorbency of cotton, making comfortable, easy-care clothing.
Q20. hard
Acrylic is preferred over natural wool for many garments because it is:
Answer: A — Cheaper, more durable and available in a wide range of colours
Acrylic garments cost less, wear well, and are easy to wash and dye. However, natural wool remains warmer and more breathable.
Q22. hard
Why are synthetic fibres UNCOMFORTABLE to wear in hot and humid weather?
Answer: A — They do not absorb sweat, so it stays on the skin
Cotton absorbs sweat and lets it evaporate, cooling the body. Synthetic fibres repel water, so sweat remains on the skin and feels sticky.
Q23. hard
Why should synthetic clothes NOT be worn while working in a kitchen or laboratory?
Answer: A — They melt and stick to the body when they catch fire, causing serious burns
Synthetic fibres melt on heating. Molten fabric sticks to the skin and causes deep burns, so cotton clothing is far safer near flames.
Q25. hard
Plastics that can be softened repeatedly by heating and remoulded are called:
Answer: A — Thermoplastics
Thermoplastics such as polythene and PVC have linear chains that slide over each other on heating, so they can be melted and reshaped many times.
Q26. hard
Plastics that once moulded CANNOT be softened again by heating are called:
Answer: A — Thermosetting plastics
Thermosetting plastics like bakelite and melamine have cross-linked chains that lock permanently on setting. They cannot be remoulded and will char rather than melt.
Q28. hard
Bakelite is used for electrical switches and handles of cooking utensils because it is:
Answer: A — A poor conductor of heat and electricity
Bakelite is a thermosetting plastic that resists heat and does not conduct electricity, making it safe for switches, plugs and pan handles.
Q30. hard
PVC, used for pipes and electric cable insulation, stands for:
Answer: A — Polyvinyl chloride
Polyvinyl chloride is a thermoplastic used for water pipes, cable insulation, raincoats and footwear because it is cheap, waterproof and durable.
Q32. hard
Plastics are used to store chemicals because they are:
Answer: A — Non-reactive - they do not react with air, water or most chemicals
Unlike metals, plastics do not corrode or react with acids and other chemicals, so they are safe for storing food, water, medicines and laboratory reagents.
Q34. hard
Materials that are broken down naturally by bacteria and other living organisms are called:
Answer: A — Biodegradable
Vegetable peels, paper, cotton cloth and wood are biodegradable - micro-organisms decompose them into simple substances that return to the soil.
Q36. hard
Burning plastic waste is harmful because it:
Answer: A — Releases poisonous gases that pollute the air and harm health
Burning plastics releases toxic fumes including dioxins and carbon monoxide, which cause respiratory problems and other serious illnesses.
Q38. hard
The '4 R principle' for tackling plastic waste stands for:
Answer: A — Reduce, Reuse, Recycle, Recover
We should first reduce our use of plastics, reuse items where possible, recycle what we can, and recover energy or materials from the rest.
Q40. hard
Why should we NOT put hot food directly in thin polythene bags?
Answer: A — Harmful chemicals from the plastic can leach into the food
Heat can cause chemicals in low-grade plastics to migrate into food, which may be harmful to health. Steel, glass or food-grade containers are safer.
Q42. hard
Recycling plastic has a limitation because:
Answer: A — Recycled plastic is usually of lower quality and adding colouring can make it harmful
Each cycle degrades the polymer, and dyes and additives used in recycling can be toxic. So reducing use matters more than relying on recycling alone.
Q44. hard
Plastics are used in healthcare for making:
Answer: A — Syringes, doctors' gloves, blood bags and many medical instruments
Disposable plastic syringes, gloves, tubes and blood bags are sterile, cheap and single-use, which prevents infections from spreading.
Q46. hard
Which of these is BIODEGRADABLE?
Answer: A — Vegetable peels
Vegetable peels, paper, wool, cotton and wood are broken down by micro-organisms. All plastics and synthetic fibres are non-biodegradable.
Q48. hard
In a burning test, a synthetic fibre such as nylon typically:
Answer: A — Melts and shrinks away, leaving a hard bead
Synthetic fibres melt because they are thermoplastic polymers. Cotton burns to a soft ash and wool smells of burning hair - a simple way to tell fibres apart.
Q50. hard
Why is a plastic chair preferred over a wooden one in some situations?
Answer: A — It is lighter, cheaper, waterproof and does not get attacked by termites
Plastic furniture resists water, insects and rot, is easy to clean and to move, and costs less than good-quality wood - though it is less durable in strong sunlight.
Q52. hard
Which statement about the manufacture of synthetic fibres is CORRECT?
Answer: A — Chemicals are made into a liquid and forced through fine holes to form filaments, which are then spun into yarn
The polymer is melted or dissolved, extruded through a spinneret with tiny holes, and the emerging filaments solidify and are twisted into yarn.
Q54. hard
Which of these is the MOST environmentally responsible practice?
Answer: A — Segregating waste into biodegradable and non-biodegradable bins
Segregation lets biodegradable waste be composted and non-biodegradable waste be recycled properly. Mixing, burning and dumping all cause pollution.
Q56. hard
Why do we still need synthetic fibres despite their disadvantages?
Answer: A — They are strong, cheap, durable and available in large amounts, and natural fibres alone cannot meet demand
The world's population needs far more fabric than cotton, wool and silk can supply. Synthetics fill the gap, so the sensible approach is to use them wisely and dispose of them responsibly.
Q59. hard
Why are the handles of screwdrivers and pliers covered with plastic?
Answer: A — Plastic is a poor conductor of electricity and protects against shocks
Plastic is an electrical insulator, so a plastic grip prevents current from passing to the user's hand if the metal touches a live wire. It also gives a comfortable grip.