AQA GCSE Chemistry
AQA GCSE Chemistry 4.5.2 Chemical Cells and Fuel Cells Exam Questions
Free AQA GCSE Chemistry exam questions for 4.5.2 Chemical Cells and Fuel Cells, with a mark scheme for every pack. Covers how chemical cells produce a voltage, batteries, rechargeable and non-rechargeable cells, and hydrogen fuel cells compared with batteries.
4.5.2 Chemical Cells and Fuel Cells exam questions
1 question pack of real past exam questions, each with its mark scheme. Do not stop after a few: answer as many as you can without notes, then mark every answer with the mark scheme. The more questions you do, the more quickly you will spot how examiners ask about each idea.
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About AQA GCSE Chemistry 4.5.2 Chemical Cells and Fuel Cells
AQA GCSE Chemistry 4.5.2 is separate Chemistry only content. You learn how chemical cells use reactions between different metals and an electrolyte to produce a voltage, how cells are combined into batteries, and why some cells can be recharged. You then study the hydrogen fuel cell and compare it with rechargeable batteries. It is in section 4.5, examined on Paper 1, and links to the reactivity series in 4.4.1 and to oxidation and reduction. Questions often give voltage data for different metal pairs, ask you to evaluate fuel cells against batteries, or at Higher tier ask for the half equations in a hydrogen fuel cell.
What you need to know
- Chemical cells A cell contains chemicals that react to produce electricity. The voltage depends on the type of electrode and the electrolyte; the bigger the difference in reactivity between the two metals, the bigger the voltage.
- Batteries A battery consists of two or more cells connected in series to give a greater voltage.
- Rechargeable or not In non-rechargeable cells such as alkaline batteries, the chemical reactions stop when a reactant is used up. Rechargeable cells can be recharged because the reactions are reversed when an external electrical current is supplied.
- Hydrogen fuel cells Supplied with hydrogen and oxygen (from air); hydrogen is oxidised to produce water, giving a potential difference. Overall: 2H2 + O2 → 2H2O.
- Fuel cells versus batteries Fuel cells produce only water, do not need recharging and can be refuelled quickly, but hydrogen is a flammable gas that is hard to store and is often made using fossil fuels. Batteries are easier to store but use toxic metal compounds and lose capacity over time.
- Half equations (Higher tier only) At the negative electrode: 2H2 → 4H+ + 4e- (oxidation). At the positive electrode: O2 + 4H+ + 4e- → 2H2O (reduction).
Common mistakes in 4.5.2 Chemical Cells and Fuel Cells
- Saying fuel cells produce no pollution at all. They only produce water when in use, but making hydrogen and the fuel cell itself can cause pollution.
- Saying cells 'store electricity'. They store chemical energy that is transferred electrically by reactions.
- Thinking two identical metals will give a voltage. The metals must be different to produce a potential difference.
- Saying the hydrogen in a fuel cell is burned. It is oxidised electrochemically, not combusted with a flame.
Try three 4.5.2 Chemical Cells and Fuel Cells exam-style questions
1. A cell is made with zinc and copper electrodes. Suggest how the voltage would change if zinc were replaced with magnesium. Explain your answer. (2 marks)
Show the mark scheme answer
The voltage would increase; because the difference in reactivity between magnesium and copper is greater than between zinc and copper.
2. Give two advantages and one disadvantage of hydrogen fuel cells compared with rechargeable batteries for powering cars. (3 marks)
Show the mark scheme answer
Advantages, any two: only product is water; do not need to be recharged, can be refuelled quickly; do not lose capacity in the same way; no toxic metal compounds to dispose of. Disadvantage: hydrogen is flammable or difficult to store, or hydrogen is often produced from fossil fuels or using electricity.
3. Write the half equation for the reaction at the positive electrode of a hydrogen fuel cell. (1 mark) Higher tier only
Show the mark scheme answer
O2 + 4H+ + 4e- → 2H2O.
4.5.2 Chemical Cells and Fuel Cells FAQs
What does AQA GCSE Chemistry 4.5.2 cover?
It covers how chemical cells and batteries produce a voltage, why some cells are rechargeable, how hydrogen fuel cells work and how fuel cells compare with rechargeable batteries.
Is 4.5.2 on combined science?
No. Chemical cells and fuel cells is separate Chemistry only content assessed on Paper 1.
How do I answer an evaluate question on fuel cells?
Give advantages and disadvantages of both fuel cells and batteries, then finish with a justified conclusion. Mention storage of hydrogen, how hydrogen is made, the only product being water and the disposal of batteries.
