Year 9 Science · Unit 2 · Lesson 16
Foundation Worksheet
Learning Goals
Match each term to its meaning
Write the letter of the correct meaning next to each term. Each letter is used once.
| Term | Letter | Meaning |
|---|---|---|
| Monomer | A. Monomers join and give off a small molecule, usually water, each time a link forms. | |
| Polymer | B. A polymer made in a factory, for example from chemicals refined from crude oil. | |
| Addition polymerisation | C. A small molecule that joins with others to form a long chain. | |
| Condensation polymerisation | D. A very large molecule made of many repeating monomer units. | |
| Synthetic polymer | E. A polymer made by a living thing, such as starch or cellulose. | |
| Natural polymer | F. Monomers with a C=C double bond open up and join end to end, with no by-product. |
1. Name the monomer used to make polyethylene. Which bond in this monomer makes addition polymerisation possible?
Sort it
Write each statement in the box for the kind of polymerisation it describes.
Addition
Condensation
Worked example: ethene to polyethylene
n CH₂=CH₂ → (–CH₂–CH₂–)ₙ
One bond of each C=C double bond opens. Each carbon atom uses its spare bond to join a carbon atom in the next monomer. The part in brackets is the repeat unit, and n is the number of monomers in the chain.
2. Propene is CH₂=CHCH₃. Follow the worked example to write the equation for making polypropylene. Keep the –CH₃ group as a side branch.
3. Draw part of a polyethylene chain made from three ethene monomers. Show every C and H atom and every bond. Put brackets around one repeat unit.
Read the data
| Substance | Shape of its molecules | Melting point (°C) |
|---|---|---|
| Ethene (a monomer) | small, 2 carbon atoms | −169 |
| LDPE | long chains with many branches | about 110 |
| HDPE | long straight chains | about 135 |
| Polypropylene | long chains with a –CH₃ on every second carbon | about 165 |
Sources: Lesson 16 (polymers); CRC Handbook (ethene).
4. By how many degrees does the melting point rise from ethene to HDPE? Which substance in Table 1 is not a solid at 25 °C?
Rise °C
5. LDPE and HDPE are both made from ethene. Use Table 1 and the idea of chains packing together to explain why HDPE melts at a higher temperature.
6. Write the repeat unit of the polymer described below. Then work backwards to write the formula of its monomer, and name the polymer.
Scenario: a mystery monomer
A factory in Sydney makes a rigid plastic for drainpipes. A section of one of its polymer chains looks like this:
–CH₂–CHCl–CH₂–CHCl–CH₂–CHCl–
7. Explain to a Year 7 student how thousands of molecules of ethene, a gas, become one solid plastic chain. Use the words monomer, double bond, addition polymerisation and repeat unit.