Fuel cells (chemistry only) - AQA GCSE Chemistry Exam Questions

Practise 21 exam-style questions on Fuel cells (chemistry only) for AQA GCSE Chemistry. Write your answer as you would in the exam and get it marked in seconds against the mark scheme, point by point, with an AI tutor on hand if you get stuck.

21 questions
1–6 marks each
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20 questions, marked as you go

Sample questions with model answers

Here are 4 of the questions in this topic, each with a model answer, an explanation of why it earns the marks and the mark scheme an examiner would use.

Question 1

1 mark

A single hydrogen fuel cell produces a potential difference of about 0.7 V. A fuel cell car needs a much higher voltage.

Suggest how a higher voltage is obtained.

Model answer

Many fuel cells are connected together in series (a fuel cell stack), so their voltages add up.

Explanation

Just as a battery is made of cells connected in series, fuel cells are joined in series to give a greater voltage. Hundreds of cells are stacked together in a fuel cell car.

Mark scheme

1 mark
connect many fuel cells together in series
allow use a stack of fuel cells; 'in series' or 'stack' needed

Question 2

2 marks

Hydrogen can be used to power vehicles either by burning it in an engine or by using it in a hydrogen fuel cell. Both methods produce water.

Burning hydrogen in air at a high temperature also produces oxides of nitrogen.

Suggest two advantages of using hydrogen in a fuel cell rather than burning it in an engine.

Model answer

A fuel cell oxidises hydrogen electrochemically instead of burning it at a high temperature, so no oxides of nitrogen are formed. It also transfers chemical energy directly into electrical energy, so less energy is wasted as heat and it is more efficient.

Explanation

In a fuel cell the hydrogen is oxidised at an electrode without a flame, so nitrogen in the air is not heated enough to react with oxygen. Fewer energy transfers also means less energy is wasted.

Mark scheme

1 mark
no oxides of nitrogen are produced (because the hydrogen is not burned at high temperature)
max 2; allow no pollutants / only water is produced
1 mark
the fuel cell transfers the chemical energy directly to electrical energy, so it is more efficient / less energy is wasted as heat
1 mark
the fuel cell has no moving parts so it is quieter / needs less maintenance

Question 3

3 marks

Calculate the volume of oxygen, at room temperature and pressure, needed to react completely with 4.0 g of hydrogen in a hydrogen fuel cell.
2H₂ + O₂ → 2H₂O

Relative atomic mass (Ar): H = 1
The volume of one mole of any gas at room temperature and pressure is 24 dm³.

Model answer

moles of H₂ = 4.0 ÷ 2 = 2.0 mol
From the equation, 2 mol H₂ reacts with 1 mol O₂, so moles of O₂ = 1.0 mol
volume of O₂ = 1.0 × 24 = 24 dm³

Explanation

Use the balanced equation to find the mole ratio: only half as many moles of oxygen as hydrogen are needed. A common error is to forget this ratio and give 48 dm³.

Mark scheme

1 mark
moles of hydrogen = 4.0 ÷ 2 = 2.0 (mol)
1 mark
moles of oxygen = 2.0 ÷ 2 = 1.0 (mol)
allow ecf
1 mark
volume = 1.0 × 24 = 24 dm³
allow ecf; 48 dm³ scores 2 marks; correct answer with no working scores 3 marks

Question 4

4 marks

Hydrogen fuel cell cars are often advertised as 'zero emission' because the only product is water.

Most hydrogen is made by reacting methane with steam. Hydrogen can also be made by the electrolysis of water.

Evaluate the claim that hydrogen fuel cell cars are 'zero emission'.

Model answer

The claim is true while the car is being driven, because the fuel cell only produces water. However, most hydrogen is made from methane, which produces carbon dioxide. Hydrogen made by electrolysis needs electricity, and if this is generated from fossil fuels, carbon dioxide is still released. Energy is also used, and emissions produced, in making the car and in compressing and transporting the hydrogen. So the cars are only close to zero emission if the hydrogen is made by electrolysis using electricity from renewable sources.

Explanation

Evaluating a claim means considering the whole life of the fuel, not just what comes out of the car. The emissions have often simply moved from the car to the place where the hydrogen is made.

Mark scheme

1 mark
the claim is true when the car is being driven, because the only product is water
max 4
1 mark
making hydrogen from methane produces carbon dioxide
allow methane is a fossil fuel
1 mark
electrolysis needs electricity, which may be generated by burning fossil fuels (releasing carbon dioxide)
1 mark
emissions are also produced when the car / fuel cell is made, or when hydrogen is transported or compressed
1 mark
conclusion: the car is only close to zero emission if the hydrogen is made by electrolysis using renewable electricity

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