Free Industrial Chemistry 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. An adhesive works by

• A. melting the two surfaces together
• B. forming intermolecular forces or chemical bonds with both surfaces while cohering strongly within itself
• C. removing all air from between the surfaces only
• D. converting one surface into the other

Explanation: A good adhesive must both adhere, sticking to each surface, and cohere, holding together internally, and it usually starts as a liquid so that it can flow into the microscopic irregularities before setting. Failure at the interface is adhesive failure while failure within the glue itself is cohesive failure. Welding, by contrast, does melt the surfaces and is not adhesion.

9. Epoxy resin adhesives are supplied as two tubes that must be mixed before use because

• A. one tube contains the solvent that evaporates
• B. the two components are the same substance at different concentrations
• C. mixing lowers the temperature of the joint
• D. the resin and the hardener react together to form cross links, setting the adhesive

Explanation: Setting is a chemical reaction between the resin and a hardener that builds a rigid cross linked network, so the two must be kept apart until the moment of use. Because no solvent has to evaporate, epoxies set even in a sealed joint and bond metals, glass and ceramics strongly. Adhesives that set by solvent evaporation, such as rubber cement, work on a quite different principle.

10. Thermoplastic adhesives such as hot melt glue set by

• A. cooling and solidifying, with no chemical change
• B. reacting chemically with the surface
• C. absorbing water from the air
• D. releasing carbon dioxide

Explanation: The adhesive is applied molten, flows into the surface irregularities and then simply freezes as it cools, so the change is physical and reheating the joint softens it again. This makes such adhesives quick and convenient but unsuitable where the joint may become warm. Thermosetting adhesives such as epoxies form permanent cross links instead.