Extraction and Uses of Metals
5 marks · EasyAluminium and steels are widely used metals and alloys in everyday life.
Describe why pure aluminium is rarely used in construction and how adding other elements strengthens it.
Mild steel and high-carbon steel are two important types of steel. State the element that is mainly mixed with iron to make these steels and describe how their properties differ.
State one typical use of high-carbon steel and explain why its properties make it suitable for this use.
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(a) Pure aluminium is rarely used because it is quite soft/weak. Alloying aluminium with other elements (such as copper, silicon or magnesium) strengthens it by disrupting the regular lattice structure, making it harder for layers to slide over each other.
(b) Carbon is mixed with iron to make both mild steel (up to 0.25% carbon) and high-carbon steel (about 0.6–1.2% carbon). Mild steel is strong, malleable, and ductile, while high-carbon steel is harder and more wear-resistant but more brittle (less malleable).
(c) High-carbon steel is used for cutting tools, such as knives, because its hardness and wear resistance keep the edge sharp.
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Marking points
B1 (a) · 1 mark · States that pure aluminium is rarely used because it is soft or weak.
B2 (a) · 1 mark · Describes how alloying with other elements (e.g., silicon, copper, magnesium) strengthens aluminium by disrupting the lattice and making it harder for layers to slide.
B3 (b) · 1 mark · Identifies carbon as the element mixed with iron to make steel.
B4 (b) · 1 mark · Describes the key property difference: mild steel is more malleable/ductile, high-carbon steel is harder but more brittle.
B5 (c) · 1 mark · States a typical use of high-carbon steel (e.g., cutting tools, knives) and links use to property (hardness/wear resistance).
Worked solution
a) Pure aluminium is rarely used because it is soft and not strong enough for most structural purposes. By adding elements such as silicon, copper, or magnesium, the atoms disrupt the regular arrangement of aluminium atoms in the lattice. This makes it more difficult for layers to slide over each other, so the alloy becomes harder and stronger.
b) Carbon is the element mainly mixed with iron to produce both mild and high-carbon steel. Mild steel (up to 0.25% carbon) is strong, malleable, and can be drawn into wires. High-carbon steel (about 0.6–1.2% carbon) is much harder and more resistant to wear, but it is also more brittle and less ductile than mild steel.
c) High-carbon steel is commonly used for cutting tools, such as knives, because its hardness allows it to stay sharp and resist wearing down during use.