Home · IGCSE Chemistry 0620 · Electrochemistry · Hydrogen-oxygen fuel cells · Practice
IGCSE · Practice questions · Hydrogen-oxygen fuel cells

Weigh up the hydrogen.

Six original Cambridge-style questions on hydrogen-oxygen fuel cells: what goes in, what comes out, and their advantages and disadvantages against petrol engines.

Original questions All questions on this page are original work, written in the Cambridge IGCSE style. They are not from past papers. They test the same concepts and skills the syllabus rewards.
Keep these straight

Hydrogen in, water and electricity out.

01
Recall
[2 marks]

State the two reactants and the only chemical product of a hydrogen-oxygen fuel cell.

  • Reactants: hydrogen and oxygen. ✓
  • Product: water. ✓
02
Recall
[2 marks]

Write the balanced equation, with state symbols, for the overall reaction in a hydrogen-oxygen fuel cell.

  • 2H2(g) + O2(g) → 2H2O(l) ✓
  • One mark for correct formulae and balancing, one for state symbols. ✓
03
Explain
[2 marks]

Explain why a hydrogen fuel-cell bus does not release carbon dioxide from its exhaust.

  • The fuel, hydrogen, contains no carbon. ✓
  • The only product of its reaction with oxygen is water. ✓
04
Analysis
[4 marks]

(Extended) Give two advantages and two disadvantages of using hydrogen fuel cells, rather than petrol engines, to power cars.

  • Advantage: only water is produced, so no carbon dioxide, carbon monoxide or oxides of nitrogen at the point of use. ✓
  • Advantage: more efficient; no fossil fuel is burned in the car. ✓
  • Disadvantage: hydrogen is a flammable gas that is difficult to store; it needs large pressurised tanks. ✓
  • Disadvantage: hydrogen is mostly made from methane or by electrolysis using electricity, and there are few refuelling stations. ✓
05
Explain
[2 marks]

(Extended) A company says its fuel-cell cars are "zero emission". Explain why this claim may be misleading.

  • The car itself emits only water. ✓
  • But the hydrogen is often made from methane, or by electrolysis using electricity from fossil fuels, which releases carbon dioxide. ✓
06
Explain
[2 marks]

Suggest why a fuel cell, unlike a battery, does not need to be recharged.

  • The reactants, hydrogen and oxygen, are supplied continuously from outside the cell. ✓
  • So it keeps producing electricity as long as the fuel supply lasts; it is refuelled rather than recharged. ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.