Storage cells and fuel cellsEdexcel A-Level Chemistry: Subtopic test

1. 1
   A car battery contains six identical lead–acid cells connected in series. Standard electrode potentials: PbO₂(s) + 4H⁺(aq) + SO₄²⁻(aq) + 2e⁻ ⇌ PbSO₄(s) + 2H₂O(l), E° = +1.69 V; PbSO₄(s) + 2e⁻ ⇌ Pb(s) + SO₄²⁻(aq), E° = −0.36 V.

   (a)

   What is the standard cell potential of one lead–acid cell when it is discharging?

   [1 mark]

   • A+1.33 V
   • B+2.05 V
   • C+4.10 V
   • D−2.05 V

   (b)

   What is the emf of the whole battery?

   [1 mark]

   • A2.05 V
   • B8.0 V
   • C12.3 V
   • D24.6 V

   (c)

   Explain why this battery can be recharged but a typical disposable cell cannot.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A bus company is testing a hydrogen–oxygen fuel cell with an alkaline electrolyte. Standard electrode potentials: O₂(g) + 2H₂O(l) + 4e⁻ ⇌ 4OH⁻(aq), E° = +0.40 V; 2H₂O(l) + 2e⁻ ⇌ H₂(g) + 2OH⁻(aq), E° = −0.83 V.

   (a)

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

   [1 mark]

   • A+1.23 V
   • B−0.43 V
   • C+0.43 V
   • D−1.23 V

   (b)

   Which statement about the electrode at which hydrogen is supplied is correct?

   [1 mark]

   • AH₂ is reduced at the positive electrode
   • BH₂ is oxidised at the positive electrode
   • CH₂ is reduced at the negative electrode
   • DH₂ is oxidised at the negative electrode

   (c)

   Deduce the overall equation for the reaction in the fuel cell, and state one environmental advantage of this fuel cell at the point of use.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A company is developing portable fuel cells that use an acidic electrolyte. One design is supplied with hydrogen gas and the other is supplied with liquid methanol. In both designs the oxidant is oxygen from the air.

   (a)

   Write the half-equation at each electrode of the hydrogen design, and the overall equation.

   [3 marks]

   (b)

   In the methanol design, methanol reacts with oxygen to form carbon dioxide and water. Write the half-equation for the reaction of methanol and the overall equation, and give one advantage and one disadvantage of methanol compared with hydrogen as the fuel.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A city transport authority is comparing buses powered by rechargeable battery packs with buses powered by hydrogen–oxygen fuel cells. The routes are long, and the buses must be back in service quickly after each shift.

   (a)

   Compare how a hydrogen–oxygen fuel cell and a rechargeable storage cell supply electrical energy.

   [6 marks]

   (b)

   Evaluate the use of hydrogen–oxygen fuel cells rather than rechargeable battery packs to power the buses.

   [6 marks]

   Total for question 4: 12 marks

End of questions