JEE Chemistry Polymers MCQs Set 20

Answer: (d) 28 kg

Explanation:
1. Molar mass of \( \ce{CaC2} \) = 40.1 + 24 = 64.1 g/mol, so 64.1 kg is 1 kmol.
2. 1 kmol \( \ce{CaC2} \) gives 1 kmol \( \ce{C2H2} \), then 1 kmol \( \ce{C2H4} \).
3. Mass of 1 kmol ethene (28 kg/kmol) = 28 kg of polyethylene.

Teacher's Note:
1. Follow the mole ratio through each step (all 1:1).
2. Polymerisation conserves mass.

Answer: (b) \( \ce{CH2=C(Cl)-CH=CH2} \)

Explanation:
1. Neoprene is poly(chloroprene).
2. Chloroprene is 2-chlorobuta-1,3-diene, \( \ce{CH2=C(Cl)-CH=CH2} \).
3. It polymerises by 1,4-addition.

Teacher's Note:
1. Neoprene: chloroprene; Buna-S: butadiene + styrene; Teflon: tetrafluoroethene.
2. Neoprene is a synthetic rubber resistant to oils.

Answer: (c) methyl methacrylate

Explanation:
1. PMMA stands for poly(methyl methacrylate).
2. Its monomer is \( \ce{CH2=C(CH3)COOCH3} \).
3. It is a transparent thermoplastic used as organic glass.

Teacher's Note:
1. Methacrylate has the extra methyl group on the alpha-carbon.
2. PMMA is known as Plexiglas or Perspex.

Answer: (d) \( \ce{H2N-CO-OC2H5} \) (ethyl carbamate)

Explanation:
1. Urethane is the ester of carbamic acid, \( \ce{H2N-COOH} \).
2. With ethanol it is ethyl carbamate, \( \ce{H2N-COOC2H5} \).

Teacher's Note:
1. Polyurethanes contain -NH-CO-O- links.
2. Carbamic acid is unstable; its esters are stable.

Answer: (a) \( \ce{HOOC(CH2)4COOH} \) and \( \ce{H2N(CH2)6NH2} \)

Explanation:
1. Nylon-6,6 is a polyamide formed by condensation of adipic acid (6 carbons) with hexamethylenediamine (6 carbons).
2. Loss of water gives amide links.

Teacher's Note:
1. The two numbers refer to the number of carbons in the diamine and the diacid.
2. Terylene (Dacron) uses terephthalic acid and glycol.

Answer: (b) I-E, II-A, III-C, IV-B

Explanation:
1. Hexamethylenediamine with adipic acid gives nylon-6,6 (E).
2. Phenol with formaldehyde gives Bakelite (A).
3. Phthalic acid with glycol gives glyptal (C).
4. Terephthalic acid with glycol gives Dacron (B).

Teacher's Note:
1. Dacron = Terylene = PET.
2. Glyptal is a polyester used in paints and lacquers.

Answer: (d) Polytetrafluoroethylene

Explanation:
1. PTFE (Teflon) has strong C-F bonds, is chemically inert, has a very low coefficient of friction and withstands high temperature.
2. These properties give a non-stick coating.

Teacher's Note:
1. Teflon: tetrafluoroethene polymer.
2. PTFE is resistant to heat and chemicals.

Answer: (c) Dynel

Explanation:
1. Dynel is the copolymer of vinyl chloride and acrylonitrile, used for wigs.
2. PVC is a homopolymer of vinyl chloride; polyacrylonitrile (Orlon/Acrilan) is a homopolymer of acrylonitrile.

Teacher's Note:
1. Copolymer = more than one type of monomer.
2. Dynel is flame resistant.

Answer: (d) acrylonitrile (vinyl cyanide)

Explanation:
1. Acrilan (Orlon) is polyacrylonitrile.
2. Its monomer is \( \ce{CH2=CH-CN} \).

Teacher's Note:
1. Polyacrylonitrile is used as artificial wool.
2. Do not confuse with PMMA (methyl methacrylate).

Answer: (b) polyamide polymer

Explanation:
1. Nylons are polyamides because the monomers are joined through amide (-CO-NH-) links.
2. Hydrogen bonding between chains gives them high tensile strength.

Teacher's Note:
1. Nylon-6 is made from caprolactam, nylon-6,6 from adipic acid and hexamethylenediamine.
2. Polyamides are fibres.

Answer: (c) Nylon-66

Explanation:
1. Bakelite is a phenol-formaldehyde resin.
2. Terylene is a polyester, Teflon a fluoropolymer.
3. Nylon-66 contains amide linkages, so it is a polyamide.

Teacher's Note:
1. Look for -CO-NH- units.
2. Proteins are natural polyamides.

Answer: (c) Teflon

Explanation:
1. Teflon is poly(tetrafluoroethene), \( \ce{(CF2-CF2)n} \), with all hydrogens replaced by fluorine.
2. PVC has Cl, thiokol has sulphur, neoprene has Cl.

Teacher's Note:
1. Teflon is made from \( \ce{CF2=CF2} \).
2. Fully fluorinated = no C-H bonds.

Answer: (a) HCHO

Explanation:
1. Bakelite is a thermosetting phenol-formaldehyde resin.
2. Phenol condenses with formaldehyde (methanal) in acid or base to give a cross-linked network.

Teacher's Note:
1. Novolac (acid, excess phenol) and resol (base, excess HCHO) are stages.
2. Heating cures Bakelite into a rigid cross-linked polymer.

Answer: (b) \( \ce{CH2=CH-CN} \) and \( \ce{CH2=CH-CH=CH2} \)

Explanation:
1. Buna-N is made from 1,3-butadiene (Bu, Na for sodium catalyst) and acrylonitrile (N).
2. Buna-S is from butadiene and styrene.

Teacher's Note:
1. Buna-N is also called nitrile rubber; oil resistant.
2. N stands for nitrile (acrylonitrile).

Answer: (d) Glyptal

Explanation:
1. Neoprene, Buna-S and PMMA are formed by addition polymerisation of unsaturated monomers.
2. Glyptal is a polyester formed by step-growth condensation of glycol and phthalic acid.

Teacher's Note:
1. Addition polymers: polyalkenes, PVC, Teflon, neoprene, Buna rubbers.
2. Condensation polymers: nylons, polyesters, Bakelite, glyptal.

Answer: (c) Polythene

Explanation:
1. Melmac (melamine-formaldehyde), Bakelite and vulcanised rubber have cross-linked networks.
2. Polythene consists of linear (HDPE) or branched (LDPE) chains without cross links.

Teacher's Note:
1. Thermosets are cross-linked.
2. Vulcanisation adds sulphur cross links.

Answer: (b) \( \ce{RSiCl3} \)

Explanation:
1. Hydrolysis of \( \ce{RSiCl3} \) gives \( \ce{RSi(OH)3} \) with three OH groups, which condense in three directions to give a cross-linked network.
2. R2SiCl2 gives linear chains, R3SiCl gives chain terminators and R4Si does not hydrolyse.

Teacher's Note:
1. Functionality of silane decides the polymer: 1 end, 2 chain, 3 network.
2. R3SiCl is used to end-cap chains.