Electrochemical cells and cell potentialsEdexcel International A Level Chemistry: Subtopic test

1. 1
   A cell is built from a zinc half-cell and a copper half-cell under standard conditions. Standard electrode potentials: Zn²⁺(aq)|Zn(s) −0.76 V; Cu²⁺(aq)|Cu(s) +0.34 V.

   (a)

   Which cell diagram is written correctly, by convention, for this cell?

   [1 mark]

   • ACu(s) | Cu²⁺(aq) ‖ Zn²⁺(aq) | Zn(s)
   • BZn²⁺(aq) | Zn(s) ‖ Cu(s) | Cu²⁺(aq)
   • CZn(s) | Zn²⁺(aq) ‖ Cu²⁺(aq) | Cu(s)
   • DZn(s) | Cu²⁺(aq) ‖ Zn²⁺(aq) | Cu(s)

   (b)

   What is E°cell for this cell?

   [1 mark]

   • A+1.10 V
   • B−1.10 V
   • C+0.42 V
   • D−0.42 V

   (c)

   Write the overall ionic equation for the cell reaction, including state symbols, and state the direction of electron flow in the external circuit.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student builds a cell from a silver half-cell and an iron(III)/iron(II) half-cell, both under standard conditions. Standard electrode potentials: Ag⁺(aq)|Ag(s) +0.80 V; Fe³⁺(aq)|Fe²⁺(aq) +0.77 V.

   (a)

   What is E°cell for this cell, and which electrode is the positive terminal?

   [1 mark]

   • A+1.57 V, with the silver electrode positive
   • B+0.03 V, with the silver electrode positive
   • C+0.03 V, with the platinum electrode positive
   • D−0.03 V, with the silver electrode positive

   (b)

   Which cell diagram, written by convention, represents this cell with a positive E°cell?

   [1 mark]

   • AAg(s) | Ag⁺(aq) ‖ Fe³⁺(aq), Fe²⁺(aq) | Pt(s)
   • BPt(s) | Fe²⁺(aq), Fe³⁺(aq) | Ag⁺(aq) | Ag(s)
   • CFe²⁺(aq), Fe³⁺(aq) ‖ Ag⁺(aq) | Ag(s)
   • DPt(s) | Fe²⁺(aq), Fe³⁺(aq) ‖ Ag⁺(aq) | Ag(s)

   (c)

   The student repeats the experiment using 0.50 mol dm⁻³ silver nitrate solution in the silver half-cell. Explain why the cell emf would no longer be the standard value of E°cell.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A data table gives these standard electrode potentials: Mg²⁺(aq)|Mg(s) −2.37 V; Ni²⁺(aq)|Ni(s) −0.25 V; Ag⁺(aq)|Ag(s) +0.80 V; Cl₂(g)|Cl⁻(aq) +1.36 V.

   (a)

   A cell is made from the Mg²⁺|Mg and Ni²⁺|Ni half-cells under standard conditions. Write the cell diagram and calculate E°cell.

   [3 marks]

   (b)

   Use the data to identify the strongest oxidising agent and the strongest reducing agent among the species listed. Calculate E°cell for the cell made from the half-cells containing these two species.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A student builds the cell Cu(s) | Cu²⁺(aq) ‖ Ag⁺(aq) | Ag(s) at 25 °C using fresh 1.00 mol dm⁻³ solutions. Standard electrode potentials: Cu²⁺(aq)|Cu(s) +0.34 V; Ag⁺(aq)|Ag(s) +0.80 V.

   (a)

   Write the half-equations and the overall equation for the spontaneous cell reaction. Calculate E°cell and state the direction of electron flow in the external circuit.

   [6 marks]

   (b)

   The student measures a cell voltage of 0.41 V, lower than the expected value of E°cell. Evaluate possible reasons for the difference, referring to the conditions needed for measuring electrode potentials.

   [6 marks]

   Total for question 4: 12 marks

End of questions