CBSE Class 8 Science Advanced Chemistry Synthetic Clothing Material and Polymer Very Short Answer Questions Set 01

Fill in the Blanks

Question 1. Synthetic fibres are also called as ________ fibres.
Answer:
Filament. Synthetic fibres are long continuous filaments, unlike natural fibres, which are short.
In simple words: Man-made fibres come out of the spinneret as long continuous filaments.

Teacher's Note:
1. Natural fibres other than silk are short; synthetic ones are continuous.
2. Remember the phrase 'continuous filament fibres'.

Question 2. ________ is the first synthetic thermosetting plastics.
Answer:
Bakelite. It was made by Leo Baekeland in 1907 by reacting phenol with formaldehyde.
In simple words: Bakelite was the first completely synthetic plastic and it is thermosetting.

Teacher's Note:
1. Bakelite is hard, stiff and an insulator.
2. Switches, plugs and handles are made from it.

Question 3. ________ doesn't stick to the material and can be easily used in non-stick pans and other cookware.
Answer:
Teflon (PTFE). Food does not stick to it and it has a high melting point.
In simple words: Teflon is the non-stick coating on cooking pans.

Teacher's Note:
1. Teflon is the brand name of polytetrafluoroethylene.
2. Its monomer is tetrafluoroethylene.

Question 4. ________ is a natural fibre, with continuous filaments which can stretch upto 1 km.
Answer:
Silk. A single silk filament can be up to about 1 km long.
In simple words: Silk is the natural fibre with very long filaments.

Teacher's Note:
1. Most natural fibres are short; silk is the exception.
2. Silk comes from the cocoon of the silkworm.

Question 5. _________ is the first artificial fibre synthesized by human beings.
Answer:
Rayon. It is the first man-made fibre and is made from wood pulp. (Nylon is the first fully synthetic fibre.)
In simple words: Rayon was the first man-made fibre; nylon was the first fully synthetic one.

Teacher's Note:
1. Keep these two 'firsts' separate.
2. Rayon is semi-synthetic because wood pulp is its raw material.

Question 6. ________ and ______ are obtained from cotton plant and sheep.
Answer:
Cotton and wool. Cotton comes from the cotton plant and wool from the fleece of sheep.
In simple words: Cotton is a plant fibre and wool is an animal fibre.

Teacher's Note:
1. Both are natural fibres.
2. Wool is also obtained from goats and yaks.

Question 7. ________ is a thread or filament from which cloth is made
Answer:
Fibre. Fibres are spun into yarn and the yarn is woven or knitted into fabric.
In simple words: A fibre is the thread from which cloth is made.

Teacher's Note:
1. Order of steps: fibre, yarn, fabric.
2. Define fibre in one line.

Question 8. ___________ is spun thread used for sewing, weaving or knitting.
Answer:
Yarn. Fibres are twisted together (spun) to make yarn.
In simple words: Spinning fibres together gives yarn.

Teacher's Note:
1. Yarn is used to weave or knit fabric.
2. Do not mix up fibre and yarn.

Question 9. Plastics are __________ in water.
Answer:
Insoluble. This is why plastic bottles and buckets can store water.
In simple words: Plastics do not dissolve in water.

Teacher's Note:
1. Insoluble in water is a general property of plastics.
2. Use it to explain why buckets are made of plastic.

Question 10. These substances are capable of moulding and casting into various shapes and sizes ________ .
Answer:
Thermoplastics. They soften on heating and can be moulded and cast into new shapes again and again; plastics in general are easy to mould.
In simple words: Thermoplastics can be melted and moulded again and again.

Teacher's Note:
1. Thermosetting plastics cannot be re-melted.
2. Plastic means 'can be moulded'.

True or False

Question 11. Natural fibres are obtained from plants and animals where as synthetic fibres are obtained by chemical processing of petrochemicals. (True / False)
Answer:
True. Cotton, wool and silk come from plants and animals, while nylon, polyester and acrylic are made from petrochemicals.
In simple words: Natural fibres come from living things; synthetic ones are made from petroleum products.

Teacher's Note:
1. Petrochemicals are chemicals obtained from petroleum.
2. Say the source of each type to earn the mark.

Question 12. Plastics are eco-friendly. (True / False)
Answer:
False. Plastics are non-biodegradable, so they pile up, block the soil, harm animals and give toxic fumes when burnt.
In simple words: Plastics do not decay, so they harm the environment.

Teacher's Note:
1. Link the answer to non-biodegradable waste.
2. Suggest reduce and recycle as the remedy.

Question 13. Teflon is special plastic on which oil and water do not stick. (True / False)
Answer:
True. Teflon is slippery and non-stick, so oil, water and food do not stick to it.
In simple words: Nothing sticks to Teflon easily.

Teacher's Note:
1. That is why it is used on frying pans.
2. Teflon is PTFE.

Question 14. Plastics are generally good conductors of electricity. (True / False)
Answer:
False. Plastics are poor conductors of electricity, so they are used to cover wires and make switches.
In simple words: Plastics do not conduct electricity.

Teacher's Note:
1. Plastic covers on wires protect us from shocks.
2. Bakelite is used for plugs and switches.

Question 15. PVC is mainly used for electrical and sanitary fittings. (True / False)
Answer:
True. PVC is used for water pipes and sanitary fittings and for covering electrical wires.
In simple words: PVC is used for pipes, fittings and wire insulation.

Teacher's Note:
1. Name the use along with the plastic.
2. PVC is a thermoplastic.

Question 16. Cooking pans have plastic handles. (True / False)
Answer:
True. The handles are made of Bakelite, a thermosetting plastic that does not melt and is a poor conductor of heat, so the handle stays cool.
In simple words: Bakelite handles do not melt and stay cool.

Teacher's Note:
1. Plastic is a poor conductor of heat.
2. The Bakelite-handle activity proves it.

Question 17. Ropes made by Rayon are used in cranes and elevators. (True / False)
Answer:
False. Ropes of nylon and polyester are used in cranes and elevators because of their high strength and elasticity. Rayon is used for shirts, ties and linings.
In simple words: Nylon and polyester ropes, not rayon, are used in cranes.

Teacher's Note:
1. Change the fibre to make the statement true.
2. Nylon is strong and elastic.

Question 18. Fabric is the material produced be weaving of knitting yarn fibres. (True / False)
Answer:
True. Weaving or knitting yarn produces fabric.
In simple words: Weaving or knitting yarn gives fabric.

Teacher's Note:
1. Order: fibre, yarn, fabric.
2. Weaving and knitting are two ways of making fabric.

Question 19. Polystyrene and PVC are thermoplastics. (True / False)
Answer:
True. Both soften on heating, harden on cooling and can be re-moulded.
In simple words: Both soften on heating, so both are thermoplastics.

Teacher's Note:
1. Thermoplastics: polythene, PVC, polystyrene.
2. Thermosetting: Bakelite, melamine.

Question 20. Nylon has high elasticity and tensile strength. (True / False)
Answer:
True. Nylon is strong and elastic, so it is used for ropes, fishing nets and parachutes.
In simple words: Nylon is strong and stretchy.

Teacher's Note:
1. Tensile strength is the load a material can bear without breaking.
2. Nylon was the strongest thread in the activity (375 g).

Match the Column

Teacher's Note:
1. Match the sure pairs first: acrylic with woollens, spandex with swimwear.
2. Learn two uses of each fibre.

Very Short Answer Type

Question 22. Give two examples each of natural and synthetic fibre.
Answer:
Natural fibres: cotton and wool (also silk and jute).
Synthetic fibres: nylon and polyester (also acrylic and spandex).
In simple words: Cotton and wool are natural; nylon and polyester are synthetic.

Teacher's Note:
1. Natural comes from plants or animals.
2. Synthetic comes from petrochemicals.

Question 23. What are the sources of raw materials for synthetic fibre ?
Answer:
The raw materials are petrochemicals, which are chemicals obtained from petroleum.
In simple words: Synthetic fibres are made from petroleum products.

Teacher's Note:
1. Petroleum is also called crude oil.
2. Rayon is the exception: it uses wood pulp.