Free Polymers MCQs with Answers

1. A polymer is a large molecule formed by

• A. the joining together of many small repeating units called monomers
• B. the breaking of a large molecule into small units
• C. mixing two liquids without any reaction
• D. heating a metal until it melts

Explanation: Thousands of monomer units link together to form a chain whose properties are quite different from those of the monomer, so gaseous ethene becomes solid polythene. The process is called polymerisation and it is either addition, in which nothing is lost, or condensation, in which a small molecule such as water is eliminated at each link. Breaking a polymer back into monomers is depolymerisation.

2. Polythene is manufactured from ethene by

• A. condensation polymerisation
• B. addition polymerisation
• C. hydrolysis
• D. esterification

Explanation: The double bond of each ethene molecule opens and the units join end to end with no atoms lost, so the empirical formula of the polymer is identical to that of the monomer. Any monomer used in addition polymerisation must therefore contain a carbon to carbon double bond. Condensation polymerisation, by contrast, expels a small molecule at every linkage.

3. Nylon is classified as a condensation polymer because during its formation

• A. no by product is formed
• B. the monomers contain double bonds that open
• C. a small molecule such as water or hydrogen chloride is eliminated at each linkage
• D. the polymer is condensed from a gas

Explanation: A diamine and a dicarboxylic acid react so that an amide linkage forms and water is expelled at each join, which is why the polymer contains fewer atoms than the sum of its monomers. Nylon is a polyamide, and terylene, formed from a diol and a diacid, is the analogous polyester. Every condensation monomer needs two functional groups so the chain can grow at both ends.

4. A thermosetting plastic differs from a thermoplastic in that a thermosetting plastic

• A. softens every time it is heated and can be remoulded
• B. dissolves readily in water
• C. conducts electricity
• D. sets permanently on first heating because cross links form between the chains

Explanation: Covalent cross links lock the chains into a rigid three dimensional network, so the material cannot be softened and remoulded and simply chars if heated strongly, which is why bakelite is used for electrical fittings and pan handles. A thermoplastic such as polythene has separate chains held only by weak forces, so it softens repeatedly on heating and can be recycled. This difference decides how each plastic is processed and whether it can be recycled.

5. The monomer used to make polyvinyl chloride, PVC, is

• A. chloroethene
• B. chloroethane
• C. ethene
• D. phenol

Explanation: Chloroethene, also called vinyl chloride, has the double bond needed for addition polymerisation and carries the chlorine that gives PVC its rigidity and flame resistance. Chloroethane is saturated and so cannot polymerise by addition, which is the distractor to watch for. PVC is used for pipes, cable insulation and flooring, and plasticisers are added when a flexible product is wanted.

6. Which of the following is a naturally occurring polymer?

• A. Polystyrene
• B. Cellulose
• C. Nylon
• D. Teflon

Explanation: Cellulose is a natural condensation polymer of beta glucose and is the main structural material of plant cell walls, as are starch, proteins, natural rubber and DNA among natural polymers. Polystyrene, nylon and teflon are all synthetic. Recognising that natural polymers vastly outnumber synthetic ones in the living world is the point of the question.

7. The major environmental problem with most addition polymers is that they

• A. dissolve in rainwater and pollute rivers
• B. react violently with air
• C. are non biodegradable, because their inert carbon backbone resists attack by microorganisms
• D. release oxygen as they age

Explanation: The saturated carbon chain has no polar groups for enzymes to attack, so plastic waste persists in landfill and in the oceans for centuries. Burning it disposes of the material but can release toxic gases, PVC giving hydrogen chloride and dioxins. Research into biodegradable and photodegradable polymers, and improved recycling of thermoplastics, addresses this directly.

8. Terylene, a polyester, is formed by the condensation of

• A. two amino acids
• B. a diol with a dicarboxylic acid
• C. two molecules of ethene
• D. glucose units

Explanation: Ethane-1,2-diol reacts with benzene-1,4-dicarboxylic acid so that ester linkages form and water is eliminated, giving a polymer used for clothing fibre and drink bottles. A diamine with a diacid would give a polyamide such as nylon instead. Each monomer must be difunctional for a chain rather than a single small molecule to result.

9. Teflon, used for non stick coatings, is a polymer of

• A. tetrafluoroethene
• B. chloroethene
• C. propene
• D. styrene

Explanation: Every hydrogen of ethene is replaced by fluorine, and the resulting carbon to fluorine bonds are so strong and the surface so non polar that the polymer is chemically inert, heat resistant and extremely slippery. This is why teflon is used in cookware and in laboratory taps and seals. Chloroethene gives PVC and styrene gives polystyrene.

10. Natural rubber is made harder and more elastic over a wide temperature range by vulcanisation, in which it is heated with

• A. carbon black
• B. sulphur, which forms cross links between the polymer chains
• C. water under pressure
• D. sodium hydroxide

Explanation: Short chains of sulphur atoms bridge the polyisoprene chains, so they can no longer slide past one another permanently and the rubber recovers its shape instead of deforming, remaining useful when hot or cold. The more sulphur is added, the harder the product becomes, with ebonite at the extreme. Carbon black is also added to tyres but acts as a reinforcing filler rather than a cross linking agent.