A good evaluation weighs a benefit against a drawback, uses the data, and ends with a decision. The decision may depend on how the product is used, not on the material alone.
This lesson is part of polymers. It uses ideas from connecting polymer structure with properties and connects to relating polymer and composite properties to uses.
How do you weigh a polymer product?
Use four short statements in order.
- Benefit: what the product does well, from the data.
- Drawback: the cost or waste it creates.
- Comparison: how it fares against an alternative.
- Decision: which option to choose, and under what condition.
Keep the decision conditional, for example “if the bag is reused at least 20 times”.
Worked example: three shopping bags
An original dataset compares three bags.
| Bag | Cost per bag (RM) | Uses before discarding | Cost per use (RM) |
|---|---|---|---|
| Thin plastic | 0.05 | 1 | 0.05 |
| Thick reusable plastic | 0.50 | 20 | 0.025 |
| Cloth | 5.00 | 100 | 0.050 |
Cost per use is the cost divided by the number of uses. Thin plastic: 0.05 ÷ 1 = RM0.05. Thick plastic: 0.50 ÷ 20 = RM0.025. Cloth: 5.00 ÷ 100 = RM0.05.
The thick reusable bag is cheapest per use. The thin bag creates one discarded bag per shopping trip, while the thick bag creates one per 20 trips, so it also produces less waste.
Writing the judgement
“The thick reusable plastic bag is the best choice if it is used about 20 times, because its cost per use is RM0.025, half that of the other two. It also produces one discarded bag for every 20 trips. However, it is still a plastic that persists in the environment, so it should be recycled or reused until it wears out.”
That answer names a benefit, a drawback, a comparison and a condition, with numbers from the table.
The mistake that costs marks
The slip is to write from opinion and ignore the table, or to give only one side. Both appear in answers that sound convincing.
| Weak answer | Problem | Better |
|---|---|---|
| “Plastic bags pollute, so cloth is best” | Ignores cost and use | Compare cost and uses per bag |
| “Plastic is cheap, so it is best” | Ignores waste | Add the drawback |
| “Cloth is best, it lasts longer” | No numbers | Give cost per use |
The claim evidence revision desk lets you practise rewriting an answer like the weak ones above.
Check yourself
A school compares a bin liner that costs RM0.40 and is used once with a reusable container that costs RM12 and is used 60 times. Find the cost per use of each and state which is cheaper.
Answer
Bin liner: 0.40 ÷ 1 = RM0.40 per use. Container: 12 ÷ 60 = RM0.20 per use.
The container is cheaper per use, at half the cost. The decision depends on cleaning, which the data does not cover, so a full answer would mention that limit.
What to study next
Test the whole section in the polymers practice set. If the structure side is unclear, revisit connecting polymer structure with properties.
For a teacher to help you write balanced evaluations, see online one-to-one Chemistry tuition.