Alloys and Uses Exam Questions

• An alloy is a mixture of two or more elements [1]
• where at least one element is a metal [1]

Examiner note: Alloys are mixtures, not compounds — the metals are not chemically bonded but mixed at the atomic level. Bronze (Cu + Sn), brass (Cu + Zn), and steel (Fe + C) are common examples.

• In a pure metal, the atoms are all the same size and arranged in regular layers [1]
• In an alloy, atoms of different sizes are present, which disrupts the regular arrangement of layers [1]
• This makes it more difficult for the layers to slide over each other, so the alloy is harder and stronger [1]

Examiner note: The key is “different sized atoms disrupt regular layers.” A common diagram shows uniform circles for pure metal (layers slide easily) versus mixed-size circles for an alloy (layers cannot slide). This is the standard IGCSE explanation.

Examiner note: You must know the composition of at least steel, brass, and bronze. Stainless steel contains chromium, which forms a protective oxide layer — this is why it does not rust.

• Stainless steel does not rust / is corrosion resistant because of its chromium content [1]
• It is harder than pure iron, so it maintains a sharp edge [1]
• It can be sterilised without corroding, which is essential in medical environments [1]

Examiner note: Pure iron would rust in the moist hospital environment, contaminating wounds. Stainless steel’s corrosion resistance and hardness make it ideal. This is a “choosing materials for uses” question — always link properties to requirements.

• Advantage: Alloys are harder / stronger / more durable / more resistant to corrosion than the pure metal [1]
• Disadvantage: Alloys may be more expensive to produce / more difficult to recycle (as the metals must be separated) / may be less ductile or malleable than the pure metal [1]

Examiner note: Pure metals are often too soft for practical use (e.g. pure gold is too soft for jewellery). Alloying improves properties but may increase cost. Pure copper is preferred for wiring because alloying reduces its conductivity.

• The copper and silver atoms are different sizes from gold atoms [1]
• They disrupt the regular arrangement of gold atoms, making the alloy harder and more durable for daily wear [1]
• The trade-off is that the gold content is lower, so 18 carat gold is less valuable per gram and has a slightly different colour than pure gold [1]

Examiner note: Higher carat = more gold = softer and more expensive. Lower carat = more alloy metals = harder but less valuable. 18 carat is a common compromise. The alloy metals also affect colour — copper gives rose gold, silver gives white gold.