1. 1
   A chemist prepares sodium chloride crystals by reacting sodium metal directly with chlorine gas, and explains the reaction to a class in terms of electron transfer between the atoms.

   (a)

   When a sodium atom reacts with chlorine, it loses one electron. What is the charge on the resulting sodium ion?

   [1 mark]

   • A+1
   • B-1
   • C+2
   • D0

   (b)

   Each chlorine atom gains one electron during this reaction. What is the charge on the resulting chloride ion?

   [1 mark]

   • A+1
   • B-1
   • C-2
   • D0

   (c)

   Explain, in terms of electron transfer, how sodium and chlorine atoms form sodium ions and chloride ions in this reaction.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A fertiliser manufacturer needs to produce ammonium sulfate, a compound formed from ammonium ions and sulfate ions, and must first work out the correct chemical formula for the compound.

   (a)

   What is the charge on the ammonium ion, NH4?

   [1 mark]

   • A-2
   • B-1
   • C+2
   • D+1

   (b)

   What is the charge on the sulfate ion, SO4?

   [1 mark]

   • A-1
   • B+1
   • C-2
   • D+2

   (c)

   Using the charges of the ammonium ion (NH4+) and the sulfate ion (SO4 2-), deduce the chemical formula of ammonium sulfate, explaining your reasoning.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A geologist studies a sample of halite (rock salt, sodium chloride) and investigates its melting point and its ability to conduct electricity, both as a solid and when dissolved in water or melted.

   (a)

   Describe, in terms of the ions present and the forces between them, the structure of sodium chloride.

   [3 marks]

   (b)

   Explain why sodium chloride has a very high melting point, and explain why solid sodium chloride does not conduct electricity but molten or aqueous sodium chloride does conduct electricity.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A materials engineer studies magnesium oxide as a refractory material used to line the inside of furnaces, because of its extremely high melting point, and investigates its bonding and its electrical behaviour in solid and molten states.

   (a)

   Describe fully, in words, how magnesium oxide is formed from magnesium and oxygen atoms, referring to electron transfer, the charges of the ions formed, and the type of bond that holds them together.

   [6 marks]

   (b)

   Explain why magnesium oxide has an extremely high melting point, making it suitable for lining furnaces, and explain how its electrical conductivity differs between the solid state and the molten state.

   [6 marks]

   Total for question 4: 12 marks

End of questions