A hydrogen-oxygen fuel cell is used to power a forklift truck in a warehouse. Explain why the only product formed during the operation of this fuel cell is water.

Edexcel GCSE Chemistry (1CH0) — 5.4 Chemical cells and fuel cells (Chem only) · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Fuel cells are increasingly being used to power vehicles in enclosed spaces such as warehouses, where exhaust emissions are a concern.

Model answer (4 marks)

A hydrogen‑oxygen fuel cell uses hydrogen as the fuel, supplied to the anode. At the anode the hydrogen is oxidised:

H₂ → 2H⁺ + 2e⁻

The electrons flow through the external circuit to the cathode, where oxygen is reduced:

O₂ + 4e⁻ + 4H⁺ → 2H₂O

Because the only reactants entering the cell are H₂ and O₂, the only chemical species that can be produced is water (H₂O).

Examiner tips

  • State the role of hydrogen and oxygen as reactants
  • Show the half‑reactions at each electrode
  • Explain that no other species are present to form additional products
  • Use the term ‘water’ explicitly

Common mistakes

  • Confusing the anode with the cathode or vice versa
  • Failing to mention that only H₂ and O₂ are supplied
  • Using the wrong half‑reaction for oxygen reduction

Mark scheme (4 marks)

  1. Hydrogen is the fuel / hydrogen is supplied to one electrode
  2. Hydrogen donates electrons at one electrode
  3. Oxygen gains electrons at the other electrode
  4. Because only hydrogen and oxygen are the reactants, the only product formed is water (H₂O)

Key terms in this question

fuel cell · hydrogen-oxygen fuel cell

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