A recycling trade-off asks you to weigh benefits against costs. Use only the information in the question, name at least one benefit and one cost, and end with a judgement that fits the situation described.
This is the last lesson in metals and reactivity. It links the extraction ideas from relating extraction to reactivity to a real-world decision.
What does a trade-off question ask?
A trade-off question gives a situation, such as a town deciding whether to recycle aluminium cans. It asks for an evaluation. A description of recycling is not enough.
An evaluation has three parts: a benefit, a cost, and a conclusion that says which side wins here and why.
How to build the answer, step by step
- Read the supplied information and underline every figure or fact.
- List the benefits the information supports: energy saved, ore conserved, waste reduced.
- List the costs it supports: collection, sorting, transport, quality of the metal.
- Calculate any saving or percentage the question asks for, showing the working.
- Write the judgement, pointing back to the figures and saying what would change the decision.
Worked example
The figures below are invented for practice. They are not real data about any metal.
Making one tonne of a metal from ore uses 120 units of energy. Recycling one tonne uses 12 units. Collecting, sorting and transporting the scrap adds 15 units per tonne.
Evaluate recycling in terms of energy.
Step 1, energy used when recycling: 12 + 15 = 27 units per tonne.
Step 2, saving per tonne: 120 − 27 = 93 units.
Step 3, percentage saving: 93 ÷ 120 × 100 = 77.5%.
Step 4, judgement: recycling saves energy even after collection and transport are counted. The saving is 93 units per tonne, or 77.5%. Recycling is worthwhile on energy grounds, but the answer could change if the scrap had to be carried a much greater distance.
Answer: a saving of 93 units per tonne (77.5%), so recycling is favoured on energy, with the transport cost noted.
The mistake to watch for
A common slip is to import statistics from memory or to argue one side only.
Mistaken answer: “Recycling is always better because it saves almost all the energy and there is no downside.”
The student used a remembered claim, ignored the cost, and used the word “always”.
The correction is to use the supplied figures, name a cost such as transport, and limit the claim to the situation described. “In this case, recycling saves 77.5% of the energy” is safer and earns more than a sweeping statement.
Check yourself
1. Invented figures: extraction uses 80 units per tonne, recycling uses 10, and collection and transport add 6. Find the net saving and the percentage.
Show answer
Recycling total: 10 + 6 = 16. Net saving: 80 − 16 = 64 units. Percentage: 64 ÷ 80 × 100 = 80%. 64 units, 80%.
2. A question gives no figures and asks you to evaluate recycling steel cans. Which two points would you include, without numbers?
Show answer
One benefit, such as less iron ore mined and less waste to landfill, and one cost, such as collecting and sorting the cans. Then a short judgement for the town in the question.
3. Why is “recycling is always better” a weak conclusion?
Show answer
It ignores the costs and conditions in the question. A strong conclusion applies to the situation given and says what would change the decision.
Where this leads next
You have now covered the whole route in this module, so the next step is the metals and reactivity practice set, which mixes every skill. The water, air and environmental chemistry module asks for the same weighing habit.
Students who know the facts but write one-sided evaluations often improve quickly with online one-to-one Chemistry tuition, where a teacher can respond to the exact paragraph you wrote.