Year 8 Science · Unit 2 · Lesson 17
Apply Worksheet
Learning Goals
Match each job to the property it turns on
Write the matching letter in the middle column. Each letter is used once.
| Job | Letter | Property |
|---|---|---|
| Overhead power cable (aluminium) | A. Reacts easily, so the heat from one strike sets it off. | |
| Wedding ring (gold) | B. Reacts with the material of bacterial cells and kills them. | |
| Matchbox striking strip (phosphorus) | C. So unreactive that it stays shiny for thousands of years. | |
| Frying pan (metal base) | D. Inert and less dense than air. | |
| Wound antiseptic (iodine) | E. Conducts heat well and has a high melting point. | |
| Party balloon gas (helium) | F. Conducts electricity well enough and has a low density. |
1. What is the difference between an unreactive element and an inert one? Give an example of each from the lesson.
Classify with a reason
For each proposal write “suitable” or “unsuitable”, and name the property that decides it.
| Proposal | Verdict | Deciding property and reason |
|---|---|---|
| a. A ship’s anchor made of steel (mostly iron) | ||
| b. A camping cooking pot made of sodium | ||
| c. A racing bicycle frame made of lead | ||
| d. A long ladder made of aluminium |
Read the data
| Metal | Electrical conductivity (silver = 100) | Melting point (°C) | What happens in damp air |
|---|---|---|---|
| Silver (Ag) | 100 | 962 | Slowly darkens (tarnishes) |
| Copper (Cu) | 95 | 1085 | Slowly forms a brown or green surface layer |
| Gold (Au) | 72 | 1064 | Stays shiny; does not corrode |
| Aluminium (Al) | 60 | 660 | Forms a thin protective surface layer; does not rust |
| Iron (Fe) | 16 | 1538 | Rusts |
| Lead (Pb) | 8 | 327 | Slowly dulls |
Source: standard data at room temperature; conductivity compared with silver and rounded to whole numbers.
2. A contact point inside a phone needs conductivity of at least 50 and a surface that stays unchanged in damp air. Which metals in Table 1 pass both rules? Then name the metals that pass this different pair of rules: conductivity of at least 50 and a melting point above 1000 °C.
Scenario: two cables, two metals
The overhead power lines strung between tall towers across the Australian outback are aluminium. The wiring inside the walls of a house is copper. Aluminium is about one-third as dense as copper.
3. Copper is the better conductor, yet the overhead lines are aluminium. Explain each choice, name the property that decides it, and explain why silver, the best conductor of all, is used for neither.
Match each job to the property it turns on
Overhead power cable (aluminium) → F; Wedding ring (gold) → C; Matchbox striking strip (phosphorus) → A; Frying pan (metal base) → E; Wound antiseptic (iodine) → B; Party balloon gas (helium) → D.
1. An unreactive element barely reacts (gold or platinum); an inert element does not react at all (helium). [2 marks: 1 difference, 1 both examples]
Classify with a reason
a: suitable; steel is strong and dense, and here a heavy anchor is exactly what the job needs. b: unsuitable; sodium reacts violently with water, including the water in food and steam. c: unsuitable; lead is very dense and weak, so the frame would be heavy and would bend. d: suitable; aluminium has low density and good strength, so the ladder is light enough to carry.
Read the data
2. Contact point: gold only (72, stays shiny; silver and copper slowly change, and aluminium forms a surface layer). Second pair of rules: copper (95, 1085 °C) and gold (72, 1064 °C); silver fails because it melts at 962 °C. [3 marks: 1 gold, 1 copper and gold, 1 silver excluded]
Show What You Know
3. Marking guide (points expected): 1 both jobs need a conductor, and copper (95) and aluminium (60) both conduct well enough, so conductivity alone does not decide; 1 an overhead line hangs between towers, so its own weight matters; 1 aluminium is about one-third as dense, so the deciding property is low density; 1 house wiring sits still in a wall and weight hardly matters, so conductivity decides and copper wins; 1 silver (100) is only slightly better than copper (95) but costs far more, which is not worth paying over hundreds of metres of wire; 1 conclusion: the same two metals rank differently because each job turns on a different property. [6 marks]
Common error to watch for: saying aluminium is used because it is the better conductor. Aluminium conducts less well than copper; it wins on low density for overhead lines.