Year 8 Science · Unit 2 · Lesson 18
Apply Worksheet
Learning Goals
1. What does it mean to say that helium is inert? Give one example of something helium will not do.
Match each technology to the property behind it
Write the matching letter in the middle column. Each letter is used once.
| Use | Letter | Property |
|---|---|---|
| Carbon fibre in a racing-bike frame | A. Has electrons free to move along its sheets, so it conducts. | |
| Titanium in a hearing implant | B. Stiff along its length, yet light. | |
| Silicon in a solar panel | C. Makes very strong magnets. | |
| Graphite in a battery electrode | D. A semiconductor that turns sunlight into an electric current. | |
| Neodymium in wind-turbine magnets | E. The body does not reject it. |
Cause and effect: same start, opposite result
Both metals react with oxygen. Fill the empty boxes so each box leads to the next (first row, then second row).
Scenario: keeping an MRI magnet cold
An MRI scanner’s magnet only works when colder than about −265 °C, so it sits for years in a bath of liquefied gas. A boiling liquid cannot be colder than its own boiling point.
| Element | Boiling point (°C) | Does it burn? |
|---|---|---|
| Nitrogen | −196 | No |
| Helium | −269 | No (inert) |
| Argon | −186 | No (inert) |
| Hydrogen | −253 | Yes, fiercely |
| Neon | −246 | No (inert) |
Source: boiling points at normal air pressure, to the nearest degree.
2. Which liquid in Table 1 is cold enough to keep the magnet below −265 °C? Explain using the data.
3. A visitor suggests liquid hydrogen instead, because it is the next coldest. Give two reasons from Table 1 why the hospital should reject this idea.
4. Argon and neon are also inert, yet neither can do this job. What does this show about choosing an element using only one property?
5. “Pure elements are always better than alloys.” Evaluate this claim. Use gold jewellery and iron objects left outdoors as your two examples.
Warm Up
1. Inert means it does not react with other substances. Examples: helium will not burn, will not combine with the metal of its container, will not change into anything else. [2 marks: 1 meaning, 1 example]
Match each technology to the property behind it
Carbon fibre in a racing-bike frame → B; Titanium in a hearing implant → E; Silicon in a solar panel → D; Graphite in a battery electrode → A; Neodymium in wind-turbine magnets → C.
Your Turn
Cause and effect: Aluminium: a thin layer of aluminium oxide forms → the oxide is tough and sticks fast, sealing the metal so the reaction stops. Iron: rust (iron oxide) forms → the rust flakes off, exposing fresh iron to further attack.
Go Deeper
2. Helium: its liquid boils at −269 °C, below −265 °C. Every other liquid boils at a higher temperature, so it could not stay cold enough. [2 marks: 1 helium, 1 data comparison]
3. (1) Liquid hydrogen boils at −253 °C, which is warmer than −265 °C, so it cannot keep the magnet cold enough. (2) Hydrogen burns fiercely, a serious fire risk in a hospital. [2 marks]
4. Being inert is necessary but not enough: argon (−186 °C) and neon (−246 °C) boil too warm. An element must have every property the job needs, so choices must weigh several properties together. [2 marks]
Show What You Know
5. Marking guide (points expected): 1 disagree: pure is not always better; 1 pure 24-carat gold is so soft a fingernail scratches it; 1 18-carat gold (alloyed with copper and silver) is harder, so it keeps its shape as a ring; 1 pure iron rusts quickly outdoors; stainless steel (iron alloyed with chromium) resists corrosion; 1 conclusion: a material is chosen for the properties the job needs, and alloys are designed to improve on pure elements. [5 marks]
Common error to watch for: in the chain, writing “aluminium does not react”. Both metals react with oxygen; the difference is what the oxide does once it has formed.