CBSE Class 8 Science Advanced Chemistry Synthetic Clothing Material and Polymer Very Short Answer Questions Set 02

Very Short Answer Type

Question 1. Name the man made fibre made of wood pulp.
Answer:
Rayon (also called viscose or artificial silk).
In simple words: Rayon is made from wood pulp.

Teacher's Note:
1. Wood pulp is cellulose.
2. Rayon is semi-synthetic.

Question 2. What are natural fibres ?
Answer:
Natural fibres are fibres obtained from plants and animals, for example cotton, jute, wool and silk.
In simple words: Fibres that come from plants and animals are natural fibres.

Teacher's Note:
1. Give two examples with the definition.
2. Most are short fibres; silk is long.

Question 3. Give other name of spandex ?
Answer:
Spandex is also called Lycra (or elastane).
In simple words: Lycra is another name for spandex.

Teacher's Note:
1. Lycra and elastane are both used.
2. Its special feature is very high elasticity.

Question 4. Who discovered bakelite ?
Answer:
Leo Baekeland, in 1907.
In simple words: Leo Baekeland made the first fully synthetic plastic, Bakelite.

Teacher's Note:
1. Remember the year 1907.
2. Bakelite is a thermosetting plastic.

Question 5. Write the brand name of poly tetra fluoro ethylene.?
Answer:
Its brand name is Teflon.
In simple words: PTFE is sold under the name Teflon.

Teacher's Note:
1. PTFE is the short form.
2. Its monomer is \( \ce{CF2=CF2} \).

Question 6. Why teflon is used in making non-stick cooking pans ?
Answer:
Teflon does not allow food to stick to it, and it has a high melting point, so it can stand the heat of cooking. This makes cooking and cleaning easy.
In simple words: Food does not stick to Teflon and it does not melt at cooking heat.

Teacher's Note:
1. Give both reasons: non-stick and high melting point.
2. It is discovered by DuPont in 1938.

Question 7. Why is it dangerous to leave plastic bags near a burning gas stove ?
Answer:
Plastic bags melt and catch fire easily when they touch a hot flame or a hot pan, and this can cause a fire or burns. Burning plastic also gives off poisonous fumes.
In simple words: Plastic bags melt and burn near a flame.

Teacher's Note:
1. Plastics are inflammable.
2. Keep plastic and synthetic cloth away from the kitchen flame.

Question 8. What is the full form of LDPE ?
Answer:
Low Density Polyethylene.
In simple words: LDPE stands for low density polyethylene.

Teacher's Note:
1. HDPE is the high density form.
2. LDPE is used for polybags.

Techie Stuff

Question 9. Name the monomers units to obtain bakelite which is a thermosetting plastic.
Answer:
The monomers are phenol and formaldehyde, which react in the presence of a catalyst to give Bakelite.
In simple words: Phenol and formaldehyde make Bakelite.

Teacher's Note:
1. Formaldehyde is also called methanal.
2. Melamine-formaldehyde is another cross-linked plastic.

Ask Yourself

Question 10. What are the polymer ?
Answer:
A polymer is a compound of very high molecular mass formed by joining a large number of small molecules (monomers).
In simple words: A polymer is a very long molecule made of many small repeating units.

Teacher's Note:
1. Poly means many.
2. Give one natural and one synthetic example.

Question 11. What is the functional unit of polymers ?
Answer:
The functional (repeating) unit of a polymer is the monomer. Many monomer units joined together make the polymer.
In simple words: The monomer is the building block that repeats.

Teacher's Note:
1. Write the general idea as n monomers give (monomer)n.
2. Mer means unit.

Question 12. What is the monomer unit of PVC ?
Answer:
The monomer of PVC is vinyl chloride, \( \ce{CH2=CH-Cl} \).
In simple words: PVC is made by joining many vinyl chloride molecules.

Teacher's Note:
1. PVC = poly(vinyl chloride).
2. Learn the formula too.

Question 13. What are the monomer units of nylon ?
Answer:
Nylon-66 is made from adipic acid and hexamethylene diamine. (Nylon-6 is made from caprolactam.)
In simple words: Adipic acid and hexamethylene diamine join to give nylon-66.

Teacher's Note:
1. The two numbers in nylon-66 are the carbon atoms in the two monomers.
2. Nylon was prepared from coal, water and air.

Question 14. What is the monomer unit of polyester ?
Answer:
Polyester such as PET (Terylene) is made from ethylene glycol and terephthalic acid.
In simple words: Ethylene glycol and terephthalic acid react to give polyester.

Teacher's Note:
1. Two monomers join through ester links.
2. These are the same monomers shown for PET in the table.

Question 15. What are the acrylic fibre ?
Answer:
Acrylic fibres are synthetic fibres that resemble wool in properties. They are warm, soft, light, cheap and resistant to moths and sunlight, and they are known as Orlon or Acrilan.
In simple words: Acrylic is a man-made fibre that behaves like wool.

Teacher's Note:
1. Use it as artificial wool for sweaters and blankets.
2. Orlon and Acrilan are the other names.

Question 16. Give an example of synthetic polymer.
Answer:
Examples: PVC, polythene, polypropylene, nylon, polyester.
In simple words: PVC and nylon are synthetic polymers.

Teacher's Note:
1. Cellulose and protein are natural polymers.
2. Give two to be safe.

Question 17. What is the other name of terylene ?
Answer:
Terylene is also called Dacron (and the polyester film is known as mylar).
In simple words: Terylene is the same as Dacron.

Teacher's Note:
1. Terylene is a type of polyester.
2. Terrycot and Terrywool contain Terylene.

Question 18. Which fibre is made up of polyester polyurethane copolymer ?
Answer:
Spandex (Lycra or elastane).
In simple words: Spandex is the polyester-polyurethane copolymer.

Teacher's Note:
1. A copolymer is made from two different monomers.
2. Spandex is very elastic.

Question 19. What is the monomer unit of polythene ?
Answer:
The monomer of polythene is ethylene (ethene), \( \ce{CH2=CH2} \), which is \( \ce{C2H4} \).
In simple words: Many ethene molecules join to make polythene.

Teacher's Note:
1. Both HDPE and LDPE come from ethene.
2. The difference is in the arrangement of chains.

Question 20. Write uses of LDPE ?
Answer:
LDPE (low density polyethylene) is used for polybags, grocery bags and for packing frozen foods and bread.
In simple words: LDPE makes carry bags and food packets.

Teacher's Note:
1. LDPE has branched chains and is soft.
2. HDPE is the stronger one used for chemical bottles.

Question 21. Which pollutant is responsible for ozone hole ?
Answer:
Chlorofluorocarbons (CFCs), used earlier in refrigerators and aerosol sprays, damage the ozone layer.
In simple words: CFCs from refrigerators and sprays break down the ozone layer.

Teacher's Note:
1. This question goes beyond the chapter.
2. CFCs release chlorine in the upper atmosphere.

Question 22. What is the monomer unit of polystyrene ?
Answer:
The monomer is styrene (vinyl benzene), \( \ce{CH2=CH-C6H5} \).
In simple words: Styrene molecules join to form polystyrene.

Teacher's Note:
1. Thermocol is a form of polystyrene.
2. Do not confuse styrene with the polymer.

Question 23. What is the brand name of PTFE ?
Answer:
Teflon.
In simple words: PTFE is sold as Teflon.

Teacher's Note:
1. PTFE = polytetrafluoroethylene.
2. It coats non-stick pans.