Fuel cellsEdexcel International A Level Chemistry: Mind map

Exam questions on Fuel cells

1. A hydrogen–oxygen fuel cell with an acidic electrolyte is used to power a small vehicle. Standard electrode potentials: 2H⁺(aq) + 2e⁻ ⇌ H₂(g) 0.00 V; O₂(g) + 4H⁺(aq) + 4e⁻ ⇌ 2H₂O(l) +1.23 V.
   Explain why the electrolyte, which allows H⁺ ions to pass from one electrode to the other, is needed in this fuel cell.2 marks
2. A hydrogen–oxygen fuel cell uses aqueous potassium hydroxide as the electrolyte.
   Write the half-equation for the reaction at the negative electrode of this fuel cell and use oxidation numbers to show that it is an oxidation.2 marks
3. A methanol fuel cell uses an acidic electrolyte. The half-equations are: anode CH₃OH(l) + H₂O(l) → CO₂(g) + 6H⁺(aq) + 6e⁻; cathode O₂(g) + 4H⁺(aq) + 4e⁻ → 2H₂O(l). Use F = 96 500 C mol⁻¹ and M(CH₃OH) = 32.0 g mol⁻¹.
   Combine the half-equations to deduce the overall equation for the reaction in the methanol fuel cell.3 marks