1. 1
   A sculptor casts a statue from bronze, an alloy made by mixing copper with tin, rather than using pure copper, because bronze is much harder and more durable. The sculptor also considers why bronze does not corrode as quickly as pure copper when left outdoors.

   (a)

   Which statement correctly defines an alloy such as bronze?

   [1 mark]

   • AA mixture of at least two elements, at least one of which is a metal
   • BA single pure element with no other substances present
   • CA compound formed by a chemical reaction between two non-metals
   • DA mixture of two gases at high pressure

   (b)

   The sculptor finds that bronze is much harder than pure copper. Which statement best explains why an alloy such as bronze is generally harder than the pure metal it is made from?

   [1 mark]

   • AAlloys contain no delocalised electrons, making them more rigid than pure metals
   • BAlloys contain fewer atoms per unit volume than pure metals, making them lighter and stronger
   • CAlloys are held together by covalent bonds, unlike pure metals which use metallic bonding
   • DThe different-sized atoms in the alloy disrupt the regular layers of the pure metal, making it harder for the layers to slide over each other

   (c)

   Explain, in terms of the arrangement of atoms, why bronze (an alloy of copper and tin) is harder than pure copper.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A construction company uses stainless steel, an alloy of iron with chromium and nickel, for kitchen equipment because it resists rusting, unlike ordinary steel made only from iron and carbon. The same company uses a different, low-carbon steel for car body panels because it needs to bend rather than shatter in a collision.

   (a)

   Which statement correctly describes the general composition of steels?

   [1 mark]

   • ASteels are made entirely of carbon with no metal present
   • BSteels are pure iron with no other elements present
   • CSteels are alloys made from iron mixed with carbon, and sometimes other metals such as chromium or nickel
   • DSteels are alloys of copper and tin only

   (b)

   The same company uses a different type of steel, containing a lower percentage of carbon, for car body panels, because this steel needs to bend and absorb energy rather than shatter in a collision. Which statement best explains why changing the amount of carbon in a steel alloy changes its properties?

   [1 mark]

   • AChanging the amount of carbon in steel has no effect on its properties at all
   • BDifferent proportions of elements in an alloy change how the atoms are arranged and how easily the layers can slide, altering properties such as hardness and flexibility
   • CSteel with more carbon always melts at a lower temperature, making it more flexible
   • DAdding carbon to steel removes all metallic bonding from the structure

   (c)

   Explain, in terms of atomic structure, why changing the proportion of carbon and other metals in a steel alloy allows manufacturers to produce steels with different properties for different uses, such as stainless steel for kitchen equipment and low-carbon steel for car body panels.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A metallurgist studies pure gold and 18-carat gold jewellery, which is an alloy of gold mixed with small amounts of copper and silver. She finds that pure gold (24-carat) is very soft and easily scratched, while the 18-carat gold alloy is much harder and more scratch-resistant. She also tests both samples for electrical conductivity.

   (a)

   Explain, in terms of atomic arrangement, why the gold alloy is harder than pure gold.

   [3 marks]

   (b)

   The metallurgist also tests both samples for electrical conductivity and finds that both pure gold and the 18-carat gold alloy conduct electricity well, though the alloy conducts slightly less well than the pure metal. Explain why both the pure gold and the alloy conduct electricity, and suggest why the alloy's conductivity is slightly lower than that of pure gold.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   An aerospace engineer is selecting a material for aircraft components and chooses an aluminium alloy, mixing aluminium with small amounts of copper, magnesium and manganese, rather than using pure aluminium. A colleague suggests that pure aluminium might be a simpler and cheaper alternative to consider.

   (a)

   Describe, in terms of atomic structure, why the aluminium alloy is stronger than pure aluminium, and explain why alloys are generally more useful than pure metals for demanding engineering applications such as aircraft manufacturing.

   [6 marks]

   (b)

   A colleague suggests that pure aluminium might be a simpler and cheaper alternative to the alloy for the aircraft components. Explain why the engineer rejects this suggestion, describing the disadvantages of using pure aluminium instead of the aluminium alloy for this application, in terms of atomic structure and resulting properties.

   [6 marks]

   Total for question 4: 12 marks

End of questions