CBSE Class 8 Science Advanced Chemistry Synthetic Clothing Material and Polymer MCQs Set 01

Answer: (d) polymers.

Explanation:
1. Plastics and synthetic fibres are built from very long molecules made by joining many small repeating units.
2. A long molecule of this kind is called a polymer, and the small repeating units are the monomers.
3. So the large units are polymers.

Teacher's Note:
1. Poly means many and mer means unit.
2. Nylon and rayon are examples of polymers, not the name of the class.

Answer: (c) glucose

Explanation:
1. Rayon is regenerated cellulose.
2. Cellulose is itself a polymer whose repeating unit is the sugar glucose.
3. So the monomer unit of rayon is glucose.

Teacher's Note:
1. Do not choose cellulose: it is the polymer, not the monomer.
2. Starch and cellulose are both made of glucose units.

Answer: (b) Terylene

Explanation:
1. Nylon-66 is a polyamide, while Bakelite and melamine are thermosetting plastics.
2. Terylene is made of repeating ester units.
3. So the polyester is Terylene.

Teacher's Note:
1. Terylene is another name for polyester (also called Dacron).
2. Poly-ester means many ester links.

Answer: (b) Starch and cellulose

Explanation:
1. Starch, cellulose and protein are made by living things, so they are natural polymers.
2. Nylon and PVC are made in factories, so they are synthetic.
3. Only option (b) lists two natural polymers: starch and cellulose.

Teacher's Note:
1. Check each name in the pair; one wrong name spoils the option.
2. Natural polymers: starch, cellulose, protein, wool, silk.

Answer: (a) cellulose

Explanation:
1. Proteins are chains of amino acids and fats are not polymers.
2. Cellulose is a long chain of glucose units.
3. So the answer is cellulose.

Teacher's Note:
1. Starch is also made of glucose, but it is not given here.
2. Link: plants store energy as starch and build cell walls from cellulose.

Answer: (d) Wool

Explanation:
1. Polyethylene, PVC and nylon are all made in factories from petroleum products.
2. Wool is obtained from sheep, so it is a natural fibre.

Teacher's Note:
1. Natural fibres come from plants and animals.
2. Cotton, jute, silk and wool are common natural fibres.

Answer: (c) Polyester

Explanation:
1. Wool and silk come from animals and cotton comes from a plant.
2. Polyester is made by people from petrochemicals.
3. So the synthetic fibre is polyester.

Teacher's Note:
1. Synthetic fibres: nylon, polyester, acrylic, spandex.
2. Rayon is semi-synthetic because it starts from wood pulp.

Answer: (b) Rayon

Explanation:
1. Rayon is shiny and lustrous and looks like silk.
2. For this reason it is called artificial silk.

Teacher's Note:
1. Rayon is made from wood pulp, so it is not truly synthetic.
2. Its silky look explains the nickname.

Answer: (b) Styrene

Explanation:
1. Terylene is a polyester, and Terrycot and Terrywool are blends in which Terylene is mixed with cotton and wool.
2. Styrene is the small molecule (monomer) from which polystyrene is made; it is not a fibre at all.
3. So the odd one out is Styrene.

Teacher's Note:
1. Terry- in a name points to Terylene.
2. Styrene gives polystyrene (thermocol), a plastic.

Answer: (d) All of these

Explanation:
1. Acrylic fibre is the one that behaves like wool.
2. Orlon and Acrilan are trade names of acrylic fibre.
3. All three names refer to the same wool-like fibre, so the answer is all of these.

Teacher's Note:
1. Learn the other names: Orlon and Acrilan for acrylic, Lycra for spandex, Dacron for polyester.
2. 'All of these' is correct when each option is a name for the same thing.

Answer: (c) acrylic

Explanation:
1. Acrylic is warm, soft, light and cheaper than wool, and it can be knitted easily.
2. So acrylic is used in place of wool.

Teacher's Note:
1. Sweaters, shawls and blankets are made from acrylic.
2. Remember: acrylic is the artificial wool.

Answer: (d) cotton

Explanation:
1. The name Polycot combines poly(ester) and cot(ton).
2. So polycot is polyester blended with cotton.

Teacher's Note:
1. Blend names usually give away the two fibres.
2. Polyester with wool gives Terry wool.

Answer: (c) cotton

Explanation:
1. Silk comes from silkworm cocoons and wool from sheep.
2. Nylon is synthetic.
3. Cotton comes from the cotton plant: cotton.

Teacher's Note:
1. Plant fibres: cotton and jute.
2. Animal fibres: wool and silk.

Answer: (d) rayon

Explanation:
1. Fibres made from cellulose burn with the smell of burning paper.
2. Rayon is made from wood pulp (cellulose), so it burns with this smell.
3. The answer is rayon.

Teacher's Note:
1. Cotton and rayon give a paper smell; wool and silk give a burning-hair smell.
2. In the book rayon is counted with the synthetic fibres, though it is semi-synthetic.

Answer: (d) Polystyrene

Explanation:
1. Thermocol is a foam form of polystyrene.
2. The answer is polystyrene.

Teacher's Note:
1. Thermocol cups and packing blocks are made of PS.
2. Polythene is used for bags and bottles.

Answer: (d) recycling of plastic product

Explanation:
1. The numbers 1 to 7 stamped on plastic articles tell which type of plastic it is.
2. They are used to sort the plastics for recycling.
3. The number therefore represents recycling.

Teacher's Note:
1. Look for the small triangle with a number on a bottle.
2. The smaller the number, the easier the plastic is to recycle.

Answer: (b) PP

Explanation:
1. Polypropylene (PP) is used for ketchup bottles, yoghurt containers, medicine bottles and automobile battery casings.
2. So the answer is PP.

Teacher's Note:
1. Match each plastic with one use from the table.
2. HDPE is used for bottles of bleach and acids.

Answer: (b) PS

Explanation:
1. Polystyrene (thermocol) is used for disposable cups and for packing fragile goods.
2. So the answer is PS.

Teacher's Note:
1. LDPE is for polybags and PVC for pipes.
2. Thermocol is another name for foamed PS.

Answer: (d) Bakelite

Explanation:
1. PVC, polystyrene and polyethylene soften on heating and are thermoplastics.
2. Bakelite, once set, cannot be softened again, so it is a thermosetting plastic.
3. The answer is Bakelite.

Teacher's Note:
1. Thermosetting plastics: Bakelite and melamine.
2. Think of 'set' as 'set for ever'.

Answer: (b) teflon

Explanation:
1. Teflon (PTFE) does not let food stick and has a high melting point.
2. So non-stick pans are coated with Teflon.

Teacher's Note:
1. Teflon is the brand name of PTFE.
2. It was discovered by DuPont in 1938.

Answer: (b) thermoplastics

Explanation:
1. Both PVC and polythene soften on heating and harden on cooling, again and again.
2. Plastics with this behaviour are thermoplastics.
3. So the answer is thermoplastics.

Teacher's Note:
1. They are plastics, not fibres.
2. Remember: PVC, polythene, polystyrene are thermoplastics.

Answer: (d) melamine

Explanation:
1. Melamine is a fire-resistant plastic.
2. Fire-fighters' uniforms are coated with it to make them flame resistant: melamine.

Teacher's Note:
1. Teflon is used for non-stick pans, not for uniforms.
2. Melamine is also used for unbreakable crockery.

Answer: (c) mouldable

Explanation:
1. Plastics can be moulded into any shape and size.
2. This property, mouldability, is why plastic articles come in so many shapes.

Teacher's Note:
1. Moulding means shaping a soft material in a mould.
2. Thermoplastics are re-moulded again and again.

Answer: (d) plastic

Explanation:
1. Iron rusts and brass is heavy and costly; wood absorbs water.
2. Plastic is light, cheap, waterproof and does not corrode, so buckets are made of plastic.

Teacher's Note:
1. Plastics do not react with water or air.
2. Think of why buckets are no longer made of iron.

Answer: (d) recycling

Explanation:
1. Burning gives toxic gases and smoke, and dumping or burying leaves the waste in the soil for years.
2. Recycling reuses the material to make new products.
3. So the best solution is recycling.

Teacher's Note:
1. Remember the 4 R's: reduce, reuse, recycle, recover.
2. Burning plastic pollutes the air.