Electrochemical cells and cell diagramsEdexcel A-Level Chemistry: Subtopic test

1. 1
   A teacher builds a cell from a zinc half-cell and a copper half-cell. Each metal strip dips into a 1.00 mol dm⁻³ solution of its own ions at 298 K, the two solutions are joined by a salt bridge, and a high-resistance voltmeter connects the metals. Standard electrode potentials: Zn²⁺(aq) + 2e⁻ ⇌ Zn(s), E° = −0.76 V; Cu²⁺(aq) + 2e⁻ ⇌ Cu(s), E° = +0.34 V.

   (a)

   What is the standard cell potential, E°cell, of this cell?

   [1 mark]

   • A−1.10 V
   • B−0.42 V
   • C+1.10 V
   • D+2.20 V

   (b)

   Which is the conventional cell diagram for this cell, written so that E°cell = +1.10 V?

   [1 mark]

   • ACu(s) | Cu²⁺(aq) || Zn²⁺(aq) | Zn(s)
   • BZn(s) | Zn²⁺(aq) || Cu²⁺(aq) | Cu(s)
   • CZn²⁺(aq) | Zn(s) || Cu(s) | Cu²⁺(aq)
   • DZn(s) || Zn²⁺(aq) | Cu²⁺(aq) || Cu(s)

   (c)

   Explain the function of the salt bridge in this cell.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student investigates a cell made from an Fe³⁺(aq)/Fe²⁺(aq) half-cell and an Ag⁺(aq)/Ag(s) half-cell. Standard electrode potentials: Fe³⁺(aq) + e⁻ ⇌ Fe²⁺(aq), E° = +0.77 V; Ag⁺(aq) + e⁻ ⇌ Ag(s), E° = +0.80 V.

   (a)

   Why must a platinum electrode be used in the Fe³⁺(aq)/Fe²⁺(aq) half-cell?

   [1 mark]

   • AIt reacts with Fe³⁺ ions to form Fe²⁺ ions
   • BIt is more reactive than iron, so it protects the Fe²⁺ ions
   • CIt is a catalyst that raises the E° of the half-cell
   • DIt is an inert conductor that carries electrons to and from the ions in solution

   (b)

   What is the standard cell potential, E°cell, of this cell?

   [1 mark]

   • A+0.03 V
   • B−0.03 V
   • C+1.57 V
   • D+0.80 V

   (c)

   Write the conventional cell diagram for this cell, including state symbols.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student wants to measure the standard electrode potential of the Cu²⁺(aq)/Cu(s) half-cell by connecting it to a standard hydrogen electrode (SHE).

   (a)

   Describe the standard hydrogen electrode, including the conditions needed.

   [3 marks]

   (b)

   The student repeats the experiment using 0.0100 mol dm⁻³ Cu²⁺(aq) and finds that the electrode potential is less positive than +0.34 V. Explain this result, and state why the value obtained is not a standard electrode potential.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A student sets up a cell from a zinc half-cell and a silver half-cell. Standard electrode potentials: Zn²⁺(aq) + 2e⁻ ⇌ Zn(s), E° = −0.76 V; Ag⁺(aq) + e⁻ ⇌ Ag(s), E° = +0.80 V. The student has zinc and silver strips, 1.00 mol dm⁻³ solutions of zinc sulfate and silver nitrate, potassium nitrate solution, filter paper and a high-resistance voltmeter.

   (a)

   Describe how the student should set up the cell and use it to determine E°cell, and write the conventional cell diagram.

   [6 marks]

   (b)

   The student then measures the potential difference of a similar cell in which the silver nitrate solution is 0.100 mol dm⁻³ and the temperature is 35 °C, using a low-resistance voltmeter. Evaluate whether the reading will equal the E°cell value in (a).

   [6 marks]

   Total for question 4: 12 marks

End of questions