12th Class Chemistry Unit 26 Polymers Short Questions

Q2.a.i.[Kevlar® is shown as a repeating structural unit: a benzene ring with a carbonyl (C=O) group on each side (one linking to the next repeat unit, one linking to an N-H), then another benzene ring also flanked by two N-H groups — i.e. the repeat unit is -C(=O)-⟨1,4-C₆H₄⟩-C(=O)-NH-⟨1,4-C₆H₄⟩-NH-, drawn with a bracket and subscript n.] Kevlar® is a thermally and mechanically very stable but flexible polymer; a section of this polymer is given below: Name the characteristic linkage and type of polymerisation in its structure.

The characteristic linkage is the amide linkage (-CO-NH-, a carbonyl group directly bonded to a nitrogen bearing an H). It is formed by condensation polymerisation.

Q2.a.ii.Identify the two functional groups that react to form it.

A carboxylic acid (-COOH) group (or the more reactive acyl chloride, -COCl) reacts with an amine (-NH₂) group; the acid/acyl-chloride and amine groups condense to form the -CONH- amide linkage, releasing water (or HCl if the acyl chloride route is used).

Q2.a.iii.Name the monomers from which it is formed.

Benzene-1,4-dicarboxylic acid (terephthalic acid, or its acyl chloride, terephthaloyl chloride) and benzene-1,4-diamine (p-phenylenediamine).

Q2.b.Explain why the reaction between an acyl chloride and ammonia is classified as a condensation reaction. Identify the small molecule that is eliminated during this reaction.

It is a condensation reaction because two molecules combine to form a larger molecule (an amide) while a small molecule is eliminated as a by-product, rather than simply adding together. The -COCl group of the acyl chloride reacts with the -NH₂/H of ammonia; a molecule of hydrogen chloride (HCl) gas is eliminated: R-COCl + NH₃ → R-CONH₂ + HCl.

Q2.c.I.[The monomers shown are ethanedioyl chloride, ClOC-CO-Cl (a dioyl chloride with two -COCl groups), and ethane-1,2-diol, HO-CH₂-CH₂-OH (a diol with two -OH groups).] For the following monomers: Predict the type of polymer formed.

A condensation polymer — specifically a polyester, since a diol is reacting with a dioyl chloride; each new ester bond forms with elimination of a molecule of HCl.

Q2.c.ii.Draw the repeat unit and a section of the expected polymer.

Repeat unit [-O-CH₂-CH₂-O-CO-CO-]ₙ. A section of the polymer: ...-O-CH₂-CH₂-O-CO-CO-O-CH₂-CH₂-O-CO-CO-...; each repeat is formed as -OH of the diol attacks -COCl of the dioyl chloride, eliminating HCl.

Q2.c.iii.Name this polymer systematically.

Poly(ethane-1,2-diyl ethanedioate).

Q2.d.i.[Monomers given: 1,6-hexanediamine, H₂N-(CH₂)₆-NH₂, and hexanedioic acid (adipic acid), HOOC-(CH₂)₄-COOH, printed in the question as "1,4-hexandioic acid acid".] For Nylon 6,6 (from 1,6-hexanediamine and 1,4-hexandioic acid acid): Name the linkage.

Q2.d.ii.Name the small molecule eliminated.

Water (H₂O).

Q2.d.iii.Draw the repeating unit.

[-NH-(CH₂)₆-NH-CO-(CH₂)₄-CO-]ₙ

Q2.e.i.For poly(chloroethene) (PVC): Name the monomer for PVC.

Chloroethene (vinyl chloride), CH₂=CHCl.

Q2.e.ii.Why can it undergo addition polymerization?

Chloroethene contains a carbon-carbon double bond (C=C). This bond can open up, allowing monomer units to link end-to-end into a long chain without loss of any atoms, which is the defining requirement for addition polymerisation.

Q2.f.State two properties of nylon that make it suitable for ropes and fishing nets.

Nylon has high tensile strength (strong and resistant to breaking, can withstand rubbing and wear) and is resistant to water wear, both of which make it durable for ropes and fishing nets used in wet, high-stress conditions. It is also stretchable/elastic, which helps it absorb strain.

Q2.g.Give two industrial applications for PVC and two for Nylon.

PVC (1) pipes and fittings for water supply, drainage and sewage systems; (2) electrical insulation for wires and cables. Nylon: (1) ropes and fishing nets/lines; (2) clothing such as stockings, activewear and swimwear (or automotive mechanical parts such as gears and bearings).

Q2.h.Draw the repeating unit of the polyester from propan-1,3-diol and benzene-1,4-dicarboxylic acid.

[-O-CH₂-CH₂-CH₂-O-CO-C₆H₄-CO-]ₙ, where the -OH groups of propan-1,3-diol (HO-CH₂CH₂CH₂-OH) have condensed with the -COOH groups of benzene-1,4-dicarboxylic acid, with loss of water at each new ester linkage.

Q2.i.State three distinct environmental problems caused by the disposal of non-degradable polymers.

(1) They stay in the environment for a very long time, accumulating in landfills, oceans and natural landscapes and causing persistent pollution. (2) They take up huge amounts of landfill space because they do not decompose, making it harder to find space for new landfills as population grows. (3) Animals, especially marine life, mistake plastic waste for food, leading to choking, internal injuries, starvation, or entanglement in debris. (A further problem is their breakdown into microplastics, which spread through soil, water and air and can enter the food chain.)

Q2.j.Name two different polymers used in artificial organs and state the specific application for each.

Poly(tetrafluoroethylene) (PTFE) is used for artificial blood vessel grafts, since its smooth surface prevents blood clots and allows it to replace or bypass blocked vessels. Polyurethane (or silicone) is used for artificial heart valves, since it is highly flexible and durable and resists clotting.

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Unit 26: Polymers — Short Questions