1. 1
   A technician is investigating the properties of four unlabelled white solids, W, X, Y and Z, found in a school store cupboard. Solid W has a melting point of 801 degrees Celsius, does not conduct electricity when solid, but conducts well when molten or dissolved in water. Solid X has a low melting point of 80 degrees Celsius, does not conduct electricity in any state, and dissolves poorly in water. Solid Y has a very high melting point above 3500 degrees Celsius, does not conduct electricity, and is extremely hard. Solid Z is shiny, has a high melting point, can be hammered into different shapes without shattering, and conducts electricity well as a solid.

   (a)

   Sodium chloride is a compound with a high melting point of 801 degrees Celsius. Which type of structure and bonding does sodium chloride have?

   [1 mark]

   • ASimple molecular, covalent bonding
   • BIonic, held together by a lattice of oppositely-charged ions
   • CGiant covalent, with strong covalent bonds throughout
   • DMetallic, with delocalised electrons

   (b)

   Solid X has a low melting point and does not conduct electricity in any state. Which type of structure does solid X most likely have?

   [1 mark]

   • AIonic lattice
   • BGiant covalent
   • CSimple molecular (covalent)
   • DMetallic

   (c)

   Explain, in terms of structure and bonding, why solid W conducts electricity when molten or dissolved in water, but not when solid.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A materials scientist is comparing two industrial samples of carbon, P and Q, that have very different physical properties despite being made of the same element. Sample P is used to make the tips of cutting tools because it is extremely hard, has a very high melting point, and does not conduct electricity. Sample Q is used as a lubricant coating and to make electrodes, because it feels slippery, has a high melting point, and conducts electricity well.

   (a)

   A student compares two forms of carbon used in industry. Sample P is used to make cutting tool tips because it is extremely hard, while sample Q is used to make pencil lubricant coatings because it feels slippery and conducts electricity. Which statement correctly identifies samples P and Q?

   [1 mark]

   • AP is diamond and Q is graphite
   • BP is graphite and Q is diamond
   • CP and Q are both diamond
   • DP and Q are both graphite

   (b)

   Sample Q conducts electricity well, while sample P does not conduct electricity at all. What is the main reason for this difference?

   [1 mark]

   • ASample Q has a lower melting point than sample P
   • BSample Q contains free ions, whereas sample P contains no ions
   • CSample P is a metal, whereas sample Q is a non-metal
   • DSample Q has delocalised electrons free to move between its layers, whereas every electron in sample P is held in a fixed covalent bond

   (c)

   Explain, in terms of structure and bonding, why sample Q conducts electricity well while sample P does not conduct electricity at all.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A materials engineer is choosing carbon-based materials for two different products: a set of surgical scalpel blades, and an electrical brush contact for an electric motor. She is comparing diamond, graphite and a fullerene called buckminsterfullerene (C60), a spherical molecule made of 60 carbon atoms.

   (a)

   Describe the structures of sample P (diamond) and sample Q (graphite), and explain why sample Q feels slippery while sample P is extremely hard.

   [3 marks]

   (b)

   The engineer also considers using buckminsterfullerene (C60) for one of the products. Explain, in terms of its structure and bonding, why C60 has very different physical properties from both diamond and graphite, and suggest why it would not be suitable for either the scalpel blades or the electrical brush contact.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   An engineering company is comparing materials for two components: a flexible plastic casing made from poly(ethene), and an electrical conducting wire made from pure copper metal. Poly(ethene) is produced from the monomer ethene, while the copper wire is drawn from a solid block of pure copper metal.

   (a)

   A factory produces plastic drink bottles from poly(ethene), made by polymerising the monomer ethene, and also produces copper wiring from pure copper metal. Explain, in terms of structure and bonding, why poly(ethene) is a flexible, low-density solid with a low melting point, while copper is a strong, dense solid with a high melting point and excellent electrical conductivity.

   [6 marks]

   (b)

   The company also considers using an alloy of copper, rather than pure copper, for a different structural component that needs to be stronger than pure copper but does not need to conduct electricity. Explain, in terms of structure and bonding, why alloying copper with another metal is likely to make it stronger than pure copper, and evaluate whether this change would also affect its ability to conduct electricity.

   [6 marks]

   Total for question 4: 12 marks

End of questions