1. 1
   In a blast furnace, iron(III) oxide reacts with carbon monoxide: Fe2O3 + 3CO → 2Fe + 3CO2.

   (a)

   What has happened to the iron in this reaction?

   [1 mark]

   • AThe iron has been oxidised, because it has gained oxygen
   • BThe iron has been reduced, because it has lost oxygen
   • CThe iron has been neither oxidised nor reduced
   • DThe iron has gained electrons and lost oxygen at the same time, so no redox change has occurred

   (b)

   What has happened to the carbon monoxide in this reaction?

   [1 mark]

   • AIt has been reduced, because it has lost oxygen
   • BIt has remained chemically unchanged
   • CIt has acted as the oxidising agent
   • DIt has been oxidised, because it has gained oxygen, forming carbon dioxide

   (c)

   Explain why this blast furnace reaction is described as a redox reaction, and identify the reducing agent.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   An engineer inspects an unprotected steel bridge support and finds a layer of rust (hydrated iron(III) oxide) has formed where the iron has been exposed to oxygen and water.

   (a)

   In terms of electron transfer, what has happened to the iron atoms during rusting?

   [1 mark]

   • AThe iron atoms have lost electrons and been oxidised
   • BThe iron atoms have gained electrons and been oxidised
   • CThe iron atoms have lost electrons and been reduced
   • DThe iron atoms have undergone no change in oxidation number

   (b)

   What has happened to the oxygen involved in the rusting process, in terms of oxidation and reduction?

   [1 mark]

   • AThe oxygen has been oxidised, since it has gained electrons
   • BThe oxygen has acted purely as a reducing agent
   • CThe oxygen has been reduced, since it has gained electrons
   • DThe oxygen has undergone no change during rusting

   (c)

   State the oxidising agent and the reducing agent in the rusting reaction, giving a reason for each.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A forensic analyst adds a few drops of acidified potassium manganate(VII) solution, which is purple, to a sample of liquid suspected of containing a reducing agent. The purple colour disappears (becomes colourless) when added to the sample.

   (a)

   Explain what this observation shows about the sample, and describe the change in oxidation number of the manganese.

   [3 marks]

   (b)

   The analyst then tests a second liquid sample by adding it to aqueous potassium iodide solution, which is colourless, and observes the solution turning brown. Explain what this colour change shows, identify what type of agent the second sample must contain, and state which of the two colour tests (manganate(VII) or iodide) relies on the sample being an oxidising agent rather than a reducing agent.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A metal recovery company recovers silver from a waste photographic solution by adding powdered zinc metal, which displaces silver from solution: Zn(s) + 2Ag+(aq) → Zn2+(aq) + 2Ag(s).

   (a)

   Explain, in terms of electron transfer and oxidation number, why this displacement reaction is classified as a redox reaction, identifying the oxidising agent, the reducing agent, and the substances oxidised and reduced.

   [6 marks]

   (b)

   The company's chemist proposes replacing the zinc with copper metal instead, to displace the silver from solution. Using the reactivity series and the ideas of oxidation and reduction, evaluate whether copper would work as effectively as zinc for recovering silver, and explain what would happen if copper were added to a solution containing zinc ions instead of silver ions.

   [6 marks]

   Total for question 4: 12 marks

End of questions