Year 9 Science · Unit 2 · Lesson 16
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Learning Goals
1. Ethene and polyethylene contain the same atoms. Give one difference in their structure and one difference in their properties.
Because… chain
Fill in the empty boxes. Each box is caused by the one before it.
2. Complete the table. Write each repeat unit in the same style as polyethylene’s, –CH₂–CH₂–.
| Monomer | Monomer formula | Repeat unit of the polymer |
|---|---|---|
| Propene | CH₂=CHCH₃ | |
| Tetrafluoroethene | CF₂=CF₂ | |
| Chloroethene | –CH₂–CHCl– |
3. Polypropylene and polyethylene are both addition polymers. Propene has a –CH₃ side group that ethene does not. Predict one way polypropylene’s properties differ from polyethylene’s, and explain your prediction using chain structure.
Read the data
| Sample | Monomer mass | Chain mass | n |
|---|---|---|---|
| A: film (ethene) | 28 | 280 000 | |
| B: pipe (ethene) | 28 | 420 000 | |
| C: conduit (chloroethene) | 125 000 | ||
| D: tub (propene) | 42 | 5000 |
Sample data: typical sizes for these polymers, not measurements of real products.
4. Show that one chloroethene monomer, C₂H₃Cl, has a relative mass of 62.5. Then fill in every empty cell of Table 1.
5. Ultra-high-molecular-weight polyethylene (UHMWPE) has about 150 000 monomers per chain. How many times longer is a UHMWPE chain than a chain in sample A? Use chain length to explain why UHMWPE is used in cut-resistant gloves, but sample A is only used as thin film.
Scenario: identify the monomer
A laboratory tests an unknown plastic. It contains only carbon and hydrogen, with twice as many hydrogen atoms as carbon atoms. It was made with no by-product. An average chain has a relative mass of 84 000 and contains 2000 monomers.
6. Calculate the relative mass of one monomer. Use this and the other clues to identify the monomer. Explain how each clue helped.
Monomer
7. A classmate says: “Ethene and polyethylene are really the same substance. They have the same atoms, in the same 1 : 2 ratio of carbon to hydrogen.” Evaluate this claim.