1. 1
   Zinc metal is placed into a solution of copper(II) sulfate. The ionic equation for the reaction is: Zn(s) + Cu²⁺(aq) → Zn²⁺(aq) + Cu(s). A student is analysing this reaction in terms of the movement of electrons.

   (a)

   Zinc metal is added to a solution of copper(II) sulfate: Zn(s) + Cu²⁺(aq) → Zn²⁺(aq) + Cu(s). What happens to the zinc atoms in terms of electrons?

   [1 mark]

   • AThey lose electrons, so they are oxidised
   • BThey gain electrons, so they are reduced
   • CThey lose electrons, so they are reduced
   • DThey gain electrons, so they are oxidised

   (b)

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

   [1 mark]

   • AThey lose two electrons, so they are oxidised
   • BThey gain two electrons, so they are reduced
   • CThey gain two electrons, so they are oxidised
   • DThey lose two electrons, so they are reduced

   (c)

   Using the ionic equation, write a half-equation for the oxidation of zinc and a half-equation for the reduction of copper(II) ions, and state the number of electrons transferred.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Molten lead bromide, PbBr₂, is electrolysed using inert electrodes. At the cathode, lead ions gain electrons to form lead atoms: Pb²⁺ + 2e⁻ → Pb. At the anode, bromide ions lose electrons to form bromine molecules: 2Br⁻ → Br₂ + 2e⁻.

   (a)

   During the electrolysis of molten lead bromide, lead ions, Pb²⁺, gain electrons at the cathode to form lead atoms. What has happened to the lead ions?

   [1 mark]

   • AThey have been oxidised, because they have gained electrons
   • BThey have been reduced, because they have lost electrons
   • CThey have been oxidised, because they have lost electrons
   • DThey have been reduced, because they have gained electrons

   (b)

   What has happened to the bromide ions at the anode?

   [1 mark]

   • AThey have been reduced, because they have gained electrons
   • BThey have been oxidised, because they have gained electrons
   • CThey have been oxidised, because they have lost electrons
   • DThey have been reduced, because they have lost electrons

   (c)

   State which electrode is the site of oxidation and which is the site of reduction during this electrolysis, giving a reason for each in terms of electron transfer.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student reacts a strip of magnesium ribbon with dilute hydrochloric acid, observing bubbles of gas forming rapidly. The ionic equation for the reaction is: Mg(s) + 2H⁺(aq) → Mg²⁺(aq) + H₂(g).

   (a)

   Magnesium ribbon is added to a solution of dilute hydrochloric acid, producing hydrogen gas and a solution of magnesium chloride, with the ionic equation: Mg(s) + 2H⁺(aq) → Mg²⁺(aq) + H₂(g). Identify, giving a reason, which species is oxidised and which is reduced in terms of electron transfer.

   [3 marks]

   (b)

   Write half-equations for the oxidation and reduction processes occurring in this reaction, and explain why this reaction is classified as a redox reaction even though no oxygen atoms are involved.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A chemistry class is investigating a series of metal displacement reactions in aqueous solution and is asked to explain, in general, why such reactions are always redox reactions, using the electron-transfer definitions.

   (a)

   Explain fully, using the electron-transfer definitions of oxidation and reduction, why displacement reactions between metals and metal salt solutions are always classified as redox reactions, using the reaction between iron and copper(II) sulfate solution, Fe(s) + Cu²⁺(aq) → Fe²⁺(aq) + Cu(s), as your example.

   [6 marks]

   (b)

   A more reactive halogen, chlorine, can displace a less reactive halogen, bromide ions, from solution: Cl_2(aq) + 2Br^-(aq) $\rightarrow$ 2Cl^-(aq) + Br_2(aq). Explain fully, using electron-transfer definitions, why this is a redox reaction, and describe how the reactivity trend down Group 7 relates to the ease of electron transfer.

   [6 marks]

   Total for question 4: 12 marks

End of questions