Unit notes and practice questions

Grade 12 Chemistry unit 4: Polymers

Everything here is for unit 4 of the Grade 12 Chemistry textbook: what the chapter covers, the short notes, practice questions with their answers, and the lesson video where one exists.

4
Cards: 10
Practice questions on unit 4: 214–240
The textbook pages for unit 4

What unit 4 covers

1.Introduction to Polymers
2.Polymerization Reactions
3.Classification of Polymers

Short notes for unit 4

The cards filed under this chapter on the Grade 12 Chemistry page. Open one at a time.

Addition versus Condensation PolymerizationReference tableMonomer requirement · By-product formation · Growth mechanism · +2

Feature	Addition Polymerization	Condensation Polymerization
Monomer requirement	Unsaturated molecules with $C=C$ or $C\equiv C$	Molecules with two or more functional groups
By-product formation	No small molecules eliminated	Eliminates small molecules like $H_2O$ or $CH_3OH$
Growth mechanism	Chain-growth (initiation, propagation, termination)	Step-growth reaction between functional groups
Polymer molar mass	Exact multiple of monomer molar mass	Less than sum of individual monomer masses
Examples	Polyethylene, PVC, Polystyrene, Teflon	Nylon 66, Dacron, Starch, Proteins

When you use it

Use this comparison to distinguish the mechanism, monomer requirements, and products of the two main polymerization types.

Watch out

Condensation polymerization requires polyfunctional monomers and always splits off a small molecule such as water.

Drafted from Grade 12 Chemistry, pages 214-240, then checked twice before it went up

Common Synthetic Addition PolymersReference tablePolyethylene (PE) · Polypropylene (PP) · Polyvinyl chloride (PVC) · +2

Polymer Name	Monomer Name	Monomer Structure	Key Application
Polyethylene (PE)	Ethylene (Ethene)	$CH_2=CH_2$	Plastic bags, squeeze bottles, trash bags
Polypropylene (PP)	Propylene (Propene)	$CH_2=CH-CH_3$	Ropes, carpets, dishwasher safe containers
Polyvinyl chloride (PVC)	Vinyl chloride	$CH_2=CHCl$	Pipes, floor tiles, raincoats
Polymethyl methacrylate (PMMA)	Methyl methacrylate	$CH_2=C(CH_3)COOCH_3$	Airplane windows, streetlights (Lucite)
Polytetrafluoroethylene (PTFE)	Tetrafluoroethylene	$CF_2=CF_2$	Non-stick cooking pans, electrical insulation

When you use it

Use this reference to match synthetic addition polymers to their monomer formulas and commercial applications.

Watch out

Do not confuse the monomer name propylene with polymer polypropylene when identifying starting materials.

Drafted from Grade 12 Chemistry, pages 214-240, then checked twice before it went up

Degree of PolymerizationFormula

n = \frac{M_{\text{polymer}}}{M_{\text{monomer}}}

n = \frac{M_{\text{polymer}}}{M_{\text{monomer}}}

$n$: degree of polymerization (number of monomer units) $1$
$M_{\text{polymer}}$: molar mass of the polymer $\text{g mol}^{-1}$
$M_{\text{monomer}}$: molar mass of the repeating monomer unit $\text{g mol}^{-1}$

When you use it

Use this formula to calculate the number of monomer units present in a polymer molecule from molar mass data.

Watch out

Both molar masses must be expressed in the exact same units, typically g/mol, before dividing.

Drafted from Grade 12 Chemistry, pages 214-240, then checked twice before it went up

Thermoplastics versus ThermosetsReference tableMolecular architecture · Response to heat · Recyclability · +2

Property	Thermoplastics	Thermosets
Molecular architecture	Linear or lightly branched chains	Extensive three-dimensional cross-linked network
Response to heat	Melt when heated, resolidify when cooled	Do not melt; decompose irreversibly at high heat
Recyclability	Recyclable (can be remelted and reshaped)	Non-recyclable
Mechanical properties	Flexible and remoldable	Hard, rigid, heat resistant, corrosion resistant
Examples	Polyethylene, PVC, Nylon, Teflon	Bakelite, Epoxy resin, Vulcanized rubber

When you use it

Use this table to classify polymers according to their molecular structure, thermal behavior, and recyclability.

Watch out

Nylon and Dacron are condensation polymers but act as thermoplastics because they lack extensive covalent cross-linking.

Drafted from Grade 12 Chemistry, pages 214-240, then checked twice before it went up

Practice questions on unit 4

10 multiple-choice questions written against this chapter, each with its answer and the reason. Try one before you open the answer.

Question 1

According to the textbook, a molecular structure built from fewer than 100 monomer units is known as what?

A.An oligomer
B.A biopolymer
C.A thermoset
D.A copolymer

Show the answer and why

Answer: A An oligomer

Why

A polymer generally contains more than 100 monomers, while structures with a lower number of monomers are called oligomers.

Question 2

Which of the following materials is an example of a natural polymer?

A.Polyvinyl chloride
B.Cellulose
C.Teflon
D.Bakelite

Show the answer and why

Answer: B Cellulose

Why

Cellulose is a natural carbohydrate polymer found in wood and cotton. Polyvinyl chloride, Teflon, and Bakelite are synthetic polymers.

Question 3

A factory in Hawassa uses propene (CH₂=CH-CH₃) as a raw material to produce synthetic ropes and carpets. What is the name of this polymer?

A.Polyethylene
B.Polyvinyl chloride
C.Polypropylene
D.Polystyrene

Show the answer and why

Answer: C Polypropylene

Why

The addition polymerization of propylene (propene) forms polypropylene, which is commonly used to manufacture ropes, carpets, and food containers.

Question 4

What is the name of the first step in addition polymerization, in which a reactive initiator starts the reaction?

A.Chain propagation step
B.Chain termination step
C.Chain transfer step
D.Chain initiation step

Show the answer and why

Answer: D Chain initiation step

Why

The addition polymerization process begins with the chain initiation step, where a reactive initiator (such as a free radical, cation, or anion) starts the reaction.

Question 5

A laboratory in Addis Ababa tests a sample of polyvinyl chloride (PVC) with a molar mass of 1.33 x 10⁵ g/mol. If the molar mass of the vinyl chloride monomer is 62.5 g/mol, what is the degree of polymerization (number of monomer units)?

A.2128
B.1050
C.4256
D.8312

Show the answer and why

Answer: A 2128

Why

The number of monomer units (n) is found by dividing the molar mass of the polymer by the molar mass of the monomer: (1.33 x 10⁵ g/mol) / (62.5 g/mol) = 2128.

Question 6

Why can thermoplastic polymers be remelted and recycled, while thermoset polymers cannot?

A.Thermoplastics are made of natural fibers, whereas thermosets are strictly synthetic.
B.Thermoplastics have linear or lightly branched chains, while thermosets consist of an extensive cross-linked three-dimensional network.
C.Thermoplastics contain carbon-carbon triple bonds, while thermosets contain only single bonds.
D.Thermoplastics undergo step-growth polymerization, while thermosets undergo chain-growth polymerization.

Show the answer and why

Answer: B Thermoplastics have linear or lightly branched chains, while thermosets consist of an extensive cross-linked three-dimensional network.

Why

Thermoplastics have linear or lightly branched chains that melt upon heating and resolidify when cooled. Thermosets are cross-linked into a rigid three-dimensional network and decompose irreversibly when heated.

Question 7

Which two monomers react together in a condensation reaction to produce Nylon 66?

A.Terephthalic acid and ethylene glycol
B.1,6-diaminohexane and 1,6-hexanedioic acid (adipic acid)
C.Vinyl chloride and methyl methacrylate
D.Styrene and tetrafluoroethylene

Show the answer and why

Answer: B 1,6-diaminohexane and 1,6-hexanedioic acid (adipic acid)

Why

Nylon 66 is a polyamide formed by the condensation reaction of 1,6-diaminohexane (hexamethylene diamine) and 1,6-hexanedioic acid (adipic acid).

Question 8

Which polymer has a very low coefficient of friction, high chemical resistance, and remains stable at temperatures between -73 °C and 260 °C?

A.Polymethyl methacrylate (PMMA)
B.Polytetrafluoroethylene (Teflon)
C.Polypropylene
D.Polystyrene

Show the answer and why

Answer: B Polytetrafluoroethylene (Teflon)

Why

Teflon (polytetrafluoroethylene or PTFE) has a low coefficient of friction, making it slippery and ideal for non-stick cooking utensils across the temperature range of -73 °C to 260 °C.

Question 9

When equimolar amounts of 1,4-benzene dicarboxylic acid (terephthalic acid) and 1,2-ethanediol (ethylene glycol) react to form Dacron, what small molecule is eliminated as a byproduct?

A.Ammonia (NH3)
B.Hydrogen chloride (HCl)
C.Water (H2O)
D.Methane (CH4)

Show the answer and why

Answer: C Water (H2O)

Why

The reaction between a dicarboxylic acid and a dihydroxy alcohol is a condensation polymerization that forms ester linkages and releases water (H₂O) as the byproduct.

Question 10

A synthetic copolymer is synthesized such that its monomer units alternate strictly in the sequence A-B-A-B-A-B. What type of copolymer is this?

A.Regular copolymer
B.Random copolymer
C.Homopolymer
D.Thermosetting polymer

Show the answer and why

Answer: A Regular copolymer

Why

A copolymer containing a sequence of monomers in regular alternating repeating units is classified as a regular copolymer, unlike a random copolymer which has no fixed pattern.

The app holds 12 questions on this unit, marked as you go. These are the first 10.

The textbook pages for unit 4

Unit 4 runs from page 214 to page 240 of the Ministry of Education edition.

Ministry of Education edition, English, 298 pages

Download the PDF

All Grade 12 Chemistry short notes

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