AQA GCSE Chemistry Foundation (8462), Foundation tier · Energy changes › Chemical cells and fuel cells
Practise Cells and batteries. 6 exam-style questions on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
Chemistry only (not in Combined Science). A cell uses chemical reactions to produce electricity. You need to know how simple cells and batteries are made, the difference between rechargeable and non-rechargeable cells, and how to use voltage data to compare the reactivity of metals and to evaluate the use of cells.
Key facts
Cell: contains chemicals that react to produce electricity
Simple cell: two different metals in contact with an electrolyte
Voltage depends on the type of electrodes and the electrolyte
Bigger difference in reactivity = bigger voltage; same metal on both sides = 0 V
Battery: two or more cells in series; the voltages add
Non-rechargeable (e.g. alkaline): stops when a reactant is used up
Rechargeable: reactions reversed when an external electrical current is supplied
Notes
Simple cells
diagram
A cell contains chemicals that react to produce electricity.
You can make a simple cell by connecting two different metals in contact with an electrolyte (a solution containing ions, such as salt solution).
The bigger the difference in reactivity between the two metals, the bigger the voltmeter reading.
The voltage of a cell depends on several factors, including the type of electrodes (which metals) and the electrolyte.
The bigger the difference in reactivity between the two metals, the bigger the voltage.
If both electrodes are the same metal, the voltage is zero.
Batteries
A battery is two or more cells connected together in series to give a bigger voltage.
The voltages of cells in series add up, e.g. three 1.5 V cells give 4.5 V.
Non-rechargeable and rechargeable
In non-rechargeable cells and batteries, the chemical reactions stop when one of the reactants has been used up. Alkaline batteries are non-rechargeable.
Rechargeable cells and batteries can be recharged because the chemical reactions are reversed when an external electrical current is supplied.
Rechargeable cells cost more to buy, but they can be reused many times, so they are cheaper over time and fewer are thrown away. They need a charger, and recharging takes time.
Non-rechargeable cells are cheap and ready to use, but they are thrown away after one use, which wastes resources and adds to landfill unless they are recycled.
How to answer each type of question
Recall: simple cells and batteries
1 to 2 marksGrade 4
Simple cell: two different metals and an electrolyte.
Battery: cells joined in series, so add the voltages.
Why a cell stops: one of the reactants has been used up.
Example. (a) Give the two things needed to make a simple cell. (2) (b) A battery is made from three cells in series. Each cell has a voltage of 2.0 V. What is the voltage of the battery? (1) (c) Explain why a non-rechargeable cell eventually stops producing electricity. (1)
Show the model answerHide the model answer
(a) two different metals (1); an electrolyte (1) (b) 3 × 2.0 = 6.0 V (1) (c) one of the reactants has been used up, so the chemical reactions stop (1)
Don’t lose marks
Saying a cell 'runs out of electricity' or 'runs out of energy'. Say one of the reactants is used up, so the reactions stop.
Saying a rechargeable cell is recharged by 'adding more chemicals'. An external electrical current reverses the reactions.
Saying the cells in a battery are joined in parallel. They are joined in series.
Expecting a voltage from two electrodes made of the same metal.
In 'evaluate' questions, only giving points for one type of cell, or giving no conclusion.
More tips
Memory tricks
'Bigger gap, bigger voltage': the further apart two metals are in the reactivity series, the bigger the voltage.
Same metal on both sides: no difference in reactivity, so 0 V.
Cells in series: just add the voltages.
REcharge = REverse: recharging reverses the chemical reactions.
The more reactive metal gives away electrons, so it is the negative electrode.
Exam technique
In data questions, quote numbers: 'magnesium gave the highest voltage, 2.6 V, so it is the most reactive'.
Learn the key wording: 'the chemical reactions are reversed when an external electrical current is supplied'.
For 'evaluate', give at least one point for each type of cell, use the data (a cost per hour is a strong point), and end with a justified conclusion.
When asked to predict a voltage, check your answer fits the pattern: tested against the same metal, a metal between two others in reactivity should give a voltage between theirs.
What each grade needs
What you need to be able to do, from the first marks up to the top grade.
Grade 3
State what a cell doesA cell contains chemicals that react to produce electricity.
Grade 4
Describe how to make a simple cellPut two different metals in contact with an electrolyte and connect them with wires, e.g. to a voltmeter.
Grade 4
Explain how a battery gives a bigger voltageA battery is two or more cells connected in series, so their voltages add together.
Grade 5
Explain why non-rechargeable cells stop workingThe chemical reactions stop when one of the reactants has been used up.
Quick recall
Cover the answers and test yourself. The app has these as flashcards that come back just before you'd forget them.
A battery for a torch is made from four identical cells connected in series, each with a voltage of 1.5 V. Calculate the total voltage of the battery.
6.0 V
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy5 marks
Cells contain chemicals that react to produce electricity.
(a) Which two things are needed to make a simple cell? Tick (✓) two boxes.[2]
Two different metals
Two pieces of the same metal
An electrolyte
A catalyst
A thermometer
(b) A battery is made from two or more cells. How are the cells connected to produce a greater voltage?[1]
(c) A torch battery contains four cells. Each cell has a voltage of 1.5 V. Calculate the voltage of the battery.[1]
(d) Alkaline batteries are non-rechargeable. Why does an alkaline battery eventually stop working?[1]
Show the answer and mark scheme
(a)Answer: Two different metals; An electrolyte
(b)Answer: In series
in series
(c)Answer: 6.0 V
6(.0) (V)
(d)Answer: One of the reactants is used up, so the chemical reactions stop.
one of the reactants has been used up (so the chemical reactions stop)
Question 2Medium5 marks
A student plans to investigate how the metal used for one electrode affects the voltage of a simple cell. The other electrode will always be copper, and the electrolyte will be copper sulfate solution.
(a) Identify the independent variable and the dependent variable.[2]
(b) Give two variables the student should control.[2]
(c) Suggest why the student should clean the surface of each metal electrode with sandpaper before use.[1]
Show the answer and mark scheme
(a)Answer: Independent: the metal used for the other electrode; dependent: the voltage of the cell.
independent variable: the metal used for the (non-copper) electrode
dependent variable: the voltage (potential difference) of the cell
(b)Answer: Concentration of copper sulfate solution; size (area) of the electrodes.
concentration of the copper sulfate solution
size (surface area) of the electrodes
distance between the electrodes
temperature
(c)Answer: To remove any oxide layer or dirt, which could otherwise affect the voltage.
to remove any oxide layer / dirt / grease from the surface, which could otherwise affect the reaction and the voltage measured