1. 1
   In a blast furnace, iron(III) oxide reacts with carbon monoxide: Fe_2O_3 + 3CO $\rightarrow$ 2Fe + 3CO_2. A student is identifying which substances are oxidised and which are reduced in this reaction, using the definitions of oxidation and reduction in terms of oxygen.

   (a)

   In this reaction, iron(III) oxide reacts with carbon monoxide to form iron and carbon dioxide: Fe_2O_3 + 3CO $\rightarrow$ 2Fe + 3CO_2. What has happened to the iron(III) oxide?

   [1 mark]

   • AIt has been oxidised, because it has gained oxygen
   • BIt has been reduced, because it has lost oxygen
   • CIt has been reduced, because it has gained oxygen
   • DIt has been oxidised, because it has lost oxygen

   (b)

   What has happened to the carbon monoxide in this reaction?

   [1 mark]

   • AIt has been oxidised, because it has gained oxygen
   • BIt has been reduced, because it has lost oxygen
   • CIt has been oxidised, because it has lost oxygen
   • DIt has been reduced, because it has gained oxygen

   (c)

   Define oxidation and reduction in terms of oxygen, and state which of these processes converts carbon monoxide into carbon dioxide.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A demonstration shows magnesium ribbon burning brightly in air to form a white powder: 2Mg(s) + O_2(g) $\rightarrow$ 2MgO(s). Students are asked to describe this reaction using the definitions of oxidation and reduction in terms of oxygen.

   (a)

   Magnesium ribbon burns in air: 2Mg + O_2 $\rightarrow$ 2MgO. What type of reaction is this, in terms of oxygen?

   [1 mark]

   • AReduction, because magnesium loses oxygen
   • BReduction, because oxygen gains electrons
   • CNeither oxidation nor reduction, since no electrons are transferred
   • DOxidation, because magnesium gains oxygen

   (b)

   In the same reaction, what happens to the oxygen gas in terms of oxidation and reduction?

   [1 mark]

   • AThe oxygen is oxidised
   • BThe oxygen is neither oxidised nor reduced, as it is an element
   • CThe oxygen is reduced, because oxidation and reduction always occur together and magnesium is oxidised
   • DThe oxygen decomposes into separate oxygen atoms

   (c)

   Explain why the reaction between magnesium and oxygen is described as a redox reaction.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student heats a mixture of black copper(II) oxide powder and hydrogen gas in a test tube, observing that the black powder turns to pink-brown copper metal and droplets of water form: CuO(s) + H_2(g) $\rightarrow$ Cu(s) + H_2O(l).

   (a)

   Copper(II) oxide reacts with hydrogen gas when heated: CuO + H_2 $\rightarrow$ Cu + H_2O. Identify, giving reasons, which substance is oxidised and which is reduced in terms of oxygen.

   [3 marks]

   (b)

   Explain why this reaction is classified as a redox reaction, and describe how the student could use the observations from the experiment to support the conclusion that a chemical reaction, rather than a physical change, has taken place.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A geology and industry class is studying how iron is extracted from iron ore in a blast furnace, focusing on the reactions involving carbon, carbon monoxide and iron(III) oxide.

   (a)

   Using the definitions of oxidation and reduction in terms of oxygen, explain fully why the extraction of iron from iron(III) oxide in the blast furnace is a redox reaction, describing the role of carbon and carbon monoxide.

   [6 marks]

   (b)

   Explain why metals less reactive than carbon, such as iron, can be extracted from their oxides by reduction with carbon, but metals more reactive than carbon, such as aluminium, cannot be extracted this way, referring to oxidation and reduction in terms of oxygen.

   [6 marks]

   Total for question 4: 12 marks

End of questions