Year 8 Science · Unit 2 · Lesson 18
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Learning Goals
Read the graph, Iron vs Iron Oxide
Study the bar chart below, then answer the questions.
Data: Winter, M. (2023). WebElements Periodic Table, Iron. University of Sheffield; Deer, Howie & Zussman (2013). Rock-Forming Minerals.
(a) Which is denser, iron or iron oxide? By how much do they differ?
(b) A construction engineer needs a strong, magnetic, dense structural material. Based on the data, should they choose iron or iron oxide? Justify your answer using at least two properties from the graph.
(c) Explain what happens at the atomic level when iron rusts that causes these property differences to emerge.
Order the steps
Number the events from 1 to 6 to show the correct order of the rusting process. Event 1 = what happens first.
| Order | Event |
|---|---|
| Iron oxide (Fe₂O₃) forms as a red-brown layer on the surface of the metal. | |
| Iron (Fe) is exposed to both oxygen and water in the environment. | |
| Because the oxide layer is porous (unlike aluminium oxide), rust does not protect the metal underneath. | |
| Iron atoms lose electrons, forming iron ions (Fe²⁺ or Fe³⁺). | |
| Rust continues to penetrate deeper into the metal, weakening the structure over time. | |
| Iron ions combine with oxygen and water to form iron oxide compounds. |
1. A student says, "Iron is used to build bridges because it is strong and magnetic, so iron oxide must also be a good building material." Using what you know about compounds and elements, evaluate this claim and explain why the student's reasoning is flawed.
2. Carbon (C) is a black solid and oxygen (O₂) is a gas that supports combustion. Carbon dioxide (CO₂) is a colourless gas used in fire extinguishers. Using this example, explain the key scientific principle about what happens to properties when elements chemically combine to form a compound.
Wrap Up
In one sentence, what was the main idea of this lesson?