1. 1
   A student heats a mixture of magnesium powder and copper(II) oxide powder, observing a bright flash and a colour change from black to grey/pink: Mg(s) + CuO(s) $\rightarrow$ MgO(s) + Cu(s). The student is asked to classify this reaction using both the oxygen and electron definitions of oxidation and reduction.

   (a)

   In the reaction Mg(s) + CuO(s) $\rightarrow$ MgO(s) + Cu(s), what type of reaction is this?

   [1 mark]

   • AAn oxidation reaction only
   • BA redox reaction, since oxidation and reduction happen at the same time
   • CA reduction reaction only
   • DNeither oxidation nor reduction, since no gases are formed

   (b)

   In terms of electron transfer, what happens to the magnesium atoms in this reaction?

   [1 mark]

   • AThey lose electrons and are oxidised
   • BThey gain electrons and are reduced
   • CThey lose electrons and are reduced
   • DThey gain electrons and are oxidised

   (c)

   Describe this reaction in terms of oxidation and reduction using BOTH the oxygen definition and the electron-transfer definition.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Several clean iron nails are placed in a beaker of blue copper(II) sulfate solution. After thirty minutes, the nails are coated with a pink-brown solid and the surrounding solution has turned pale green.

   (a)

   Iron nails are placed in a blue solution of copper(II) sulfate. After some time, the nails become coated with a pink-brown solid and the solution turns pale green. Which ionic equation correctly represents this reaction?

   [1 mark]

   • AFe²⁺(aq) + Cu(s) → Fe(s) + Cu²⁺(aq)
   • BFe(s) + Cu²⁺(aq) → Fe²⁺(aq) + Cu(s)
   • CFe(s) + Cu²⁺(aq) → Fe³⁺(aq) + Cu(s)
   • DFe(s) + SO₄²⁻(aq) → FeSO₄(s)

   (b)

   Why does this displacement reaction occur?

   [1 mark]

   • ABecause iron is more reactive than copper
   • BBecause copper is more reactive than iron
   • CBecause both metals have exactly the same reactivity
   • DBecause copper(II) sulfate is an alkali

   (c)

   Write half-equations for the oxidation and reduction reactions occurring, and state which species is the oxidising agent.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A technician electrolyses copper(II) sulfate solution using two copper electrodes connected to a power supply, in order to purify a sample of impure copper by transferring it from the anode to the cathode.

   (a)

   During the electrolysis of copper sulfate solution using copper electrodes, copper is deposited on the cathode while the anode dissolves. Using electron-transfer definitions, explain which electrode reaction is oxidation and which is reduction.

   [3 marks]

   (b)

   Explain why this electrolysis is described as a redox process overall, and describe what would be observed happening to the mass of each electrode over time as the electrolysis proceeds.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A demonstration of the thermite reaction is carried out, in which aluminium powder reacts vigorously with iron(III) oxide powder to produce molten iron and aluminium oxide: 2Al(s) + Fe_2O_3(s) $\rightarrow$ Al_2O_3(s) + 2Fe(l).

   (a)

   Using both the oxygen and electron-transfer definitions of oxidation and reduction, explain fully why the thermite reaction between aluminium powder and iron(III) oxide, 2Al(s) + Fe_2O_3(s) $\rightarrow$ Al_2O_3(s) + 2Fe(l), is classified as a redox reaction, and explain why aluminium is able to reduce iron(III) oxide.

   [6 marks]

   (b)

   The thermite reaction is highly exothermic and is used industrially to weld railway tracks together. Explain why the oxygen-based definitions of oxidation and reduction can always be applied to this reaction, but discuss why the electron-transfer definitions are considered more generally useful across all of chemistry, including reactions where no oxygen is transferred at all.

   [6 marks]

   Total for question 4: 12 marks

End of questions