Iron is extracted from iron ore in a blast furnace. However, pure iron is rarely used in construction. Instead, iron is converted into steel, an alloy. Explain why steel is more useful than pure iron for construction purposes, and describe one way in which the composition of steel can be changed to make it suitable for a specific use.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Steel is one of the most widely used materials in the world. It is produced by altering the composition of iron extracted from the blast furnace. Different types of steel can be made by changing what is added to the iron.
Model answer (5 marks)
Pure iron has a regular crystal lattice that allows the layers of atoms to slide over each other easily, so it is soft and easily deformed. This makes it too weak for construction.
In steel, other atoms such as carbon are added. These atoms distort the regular lattice and block the movement of the layers, making the metal harder and stronger.
For example, increasing the carbon content gives high‑carbon steel, which is harder and is used for cutting tools. Adding chromium and nickel gives stainless steel, which is corrosion‑resistant and is used for cutlery and medical instruments.
In steel, other atoms such as carbon are added. These atoms distort the regular lattice and block the movement of the layers, making the metal harder and stronger.
For example, increasing the carbon content gives high‑carbon steel, which is harder and is used for cutting tools. Adding chromium and nickel gives stainless steel, which is corrosion‑resistant and is used for cutlery and medical instruments.
Examiner tips
- Use the term "regular crystal lattice" and "layers slide" to show understanding of iron’s softness.
- Explain how added atoms distort the lattice to increase hardness and strength.
- Give a specific example of a composition change and its application.
- Use correct terminology: high‑carbon steel, stainless steel, corrosion‑resistant.
Common mistakes
- Confusing iron with steel in the first part, or saying steel is softer than iron.
- Failing to mention that added atoms block layer movement.
- Giving an irrelevant example of composition change, e.g. only mentioning alloying with aluminium without linking to a specific use.
Mark scheme (5 marks)
- Pure iron has a regular arrangement of atoms/layers that can slide over each other easily
- This makes pure iron soft/too malleable/easily deformed, so it is not strong enough for construction
- In steel, other atoms (e.g. carbon) are added which distort the regular arrangement / disrupt the layers
- This makes steel harder/stronger/less easy to deform than pure iron
- A named example of how steel composition can be changed for a specific use, e.g. adding more carbon to make high-carbon steel which is harder/used for cutting tools; or adding chromium/nickel to make stainless steel which is corrosion-resistant/used for cutlery or medical instruments
Key terms in this question
Related
- All OCR A-Level Chemistry B: Salters (H433) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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