1. 1
   When magnesium ribbon burns in air, it reacts with oxygen to form magnesium oxide, releasing a bright white light.

   (a)

   In terms of oxygen, what type of reaction is this for the magnesium?

   [1 mark]

   • AReduction, because magnesium gains oxygen
   • BOxidation, because magnesium gains oxygen
   • CReduction, because magnesium loses oxygen
   • DNeutralisation, because a salt is formed

   (b)

   If iron oxide is reduced by carbon in a blast furnace to form iron metal and carbon dioxide, what happens to the iron oxide in terms of oxygen?

   [1 mark]

   • AIt gains oxygen
   • BIt gains electrons only, with no change in oxygen
   • CIt loses oxygen
   • DIts oxygen content stays exactly the same

   (c)

   Give the definitions of oxidation and reduction in terms of oxygen, and state which of these two definitions applies to the burning of magnesium described above.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   In a school experiment, zinc granules are added to copper(II) sulfate solution. Blue colour fades from the solution, and a reddish-brown coating of copper forms on the zinc.

   (a)

   In terms of electrons, what happens to the zinc atoms?

   [1 mark]

   • AZinc atoms lose electrons and are oxidised
   • BZinc atoms gain electrons and are reduced
   • CZinc atoms neither gain nor lose electrons
   • DZinc atoms gain electrons and are oxidised

   (b)

   What happens to the copper(II) ions in this experiment, in terms of electrons?

   [1 mark]

   • AThey lose electrons and are oxidised
   • BThey remain unchanged in the solution
   • CThey lose electrons and are reduced
   • DThey gain electrons and are reduced

   (c)

   Define oxidation and reduction in terms of electrons, and explain why this reaction between zinc and copper(II) sulfate solution is called a redox reaction.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A teacher demonstrates two reactions to a class. In Reaction 1, hydrogen gas is passed over heated copper(II) oxide, producing copper metal and water.

   (a)

   Explain Reaction 1 in terms of both the oxygen definition and the electron definition of oxidation and reduction.

   [3 marks]

   (b)

   In Reaction 2, magnesium ribbon is added to iron(II) sulfate solution, and a grey coating of iron forms on the magnesium. Explain Reaction 2 in terms of the electron definitions of oxidation and reduction, and explain why both Reaction 1 and Reaction 2 are examples of redox reactions.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A chemistry textbook states that oxidation and reduction can be defined either in terms of oxygen or in terms of electrons.

   (a)

   Using the reduction of iron(III) oxide by carbon in a blast furnace as an example, explain both definitions of oxidation and reduction and show how they apply consistently to this reaction.

   [6 marks]

   (b)

   Evaluate why chemists find it useful to have both the oxygen definition and the electron definition of oxidation and reduction, giving examples of reactions where one definition might be easier to apply than the other.

   [6 marks]

   Total for question 4: 12 marks

End of questions