Solder is an alloy traditionally made from tin and lead. Suggest why solder is more useful than either pure tin or pure lead for joining electrical components.

Cambridge International IGCSE Chemistry (0620) — 9.3 Alloys and their properties · Suggest · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Solder is widely used in the electronics industry to form permanent electrical connections between components on circuit boards. It must melt at a relatively low temperature and solidify quickly to form a firm joint.

Model answer (4 marks)

Solder melts at a lower temperature than pure tin or pure lead, so less heat is required and delicate components are not damaged. The mixture of tin and lead atoms of different sizes disturbs the crystal lattice, giving the alloy a higher hardness and strength than either metal alone, which produces a firm, durable joint.

Examiner tips

Use the word "lower" to show the melting point advantage. Mention the heat‑safety benefit. Explain the lattice disruption. Show that the alloy is harder/stronger for a solid joint.

Common mistakes

Failing to state the lower melting point. Confusing the alloy’s strength with that of pure metals. Using vague terms like "better" without explanation.

Mark scheme (4 marks)

Solder has a lower melting point than either pure tin or pure lead alone
A lower melting point means less heat is needed, preventing damage to delicate electronic components
The atoms of tin and lead are different sizes, disrupting the regular lattice arrangement
This makes solder harder/stronger than either pure metal, so it forms a firm, durable joint

Key terms in this question

alloy