Chemical cells & fuel cells (Chem only) – GCSE Chemistry exam questions with mark scheme

1Grade 4–5Triple only4 marks

The diagram shows a simple chemical cell.

(a) Give two factors that affect the voltage of a cell. [2]

(b) Suggest what would happen to the reading on the voltmeter if both electrodes were made of zinc. [1]

(a) the type of electrode / metals used allow difference in reactivity of the two metals(1)
(a) the electrolyte used allow concentration of electrolyte(1)
(b) reading is zero / no voltage(1)
(c) one of the reactants is used up(1)
Answer: (a) the metals used and the electrolyte (b) zero (c) a reactant gets used up
Examiner tip: Voltage comes from the difference in reactivity of the two metals — two identical metals give 0 V.

2Grade 6–7HigherTriple only5 marks

Hydrogen fuel cells are used to power some vehicles.

(a) Write the overall balanced equation for the reaction in a hydrogen fuel cell. [1]

(b) Complete the half equations at each electrode. [2]

$\text{H}_2 \rightarrow \ldots\ldots$ $\text{O}_2 + 4\text{H}^+ + \ldots\ldots \rightarrow \ldots\ldots$

(a) $2\text{H}_2 + \text{O}_2 \rightarrow 2\text{H}_2\text{O}$ allow multiples / fractions, e.g. $\text{H}_2 + \tfrac{1}{2}\text{O}_2 \rightarrow \text{H}_2\text{O}$ ignore state symbols(1)
(b) $\text{H}_2 \rightarrow 2\text{H}^+ + 2\text{e}^-$ allow $2\text{H}_2 \rightarrow 4\text{H}^+ + 4\text{e}^-$ / $\text{H}_2 - 2\text{e}^- \rightarrow 2\text{H}^+$(1)
(b) $\text{O}_2 + 4\text{H}^+ + 4\text{e}^- \rightarrow 2\text{H}_2\text{O}$(1)
(c) any two from (1 mark each): hydrogen is flammable / explosive; hydrogen is a gas so is difficult to store / needs a large volume or high pressure; hydrogen is often made from fossil fuels / using non-renewable energy allow producing hydrogen (e.g. by electrolysis) needs a lot of energy; few hydrogen refuelling stations; fuel cells cost more to make / buy ignore 'expensive' / 'cost' unqualified do not accept fuel cells produce pollution / CO₂ / harmful waste (the only product is water)(1)
(c) second disadvantage from the list above(1)
Answer: (a) 2H₂ + O₂ → 2H₂O (b) H₂ → 2H⁺ + 2e⁻; O₂ + 4H⁺ + 4e⁻ → 2H₂O (c) e.g. hydrogen is flammable/explosive and hard to store; hydrogen is often made using fossil fuels; few refuelling stations
Examiner tip: Check charge balances in half equations: 4H⁺ needs 4e⁻ on the same side to give neutral water.

3Grade 1–3FoundationTriple only5 marks

Cells and batteries are used to power torches, clocks and toys.

(a) What is a battery? [1]

(b) A student sets up three simple cells. Which cell, A, B or C, produces a voltage? [1]

Cell	Electrode 1	Electrode 2	Liquid
A	copper	copper	sodium chloride solution
B	zinc	copper	sodium chloride solution
C	zinc	zinc	sodium chloride solution

(d) Give one environmental advantage of using rechargeable cells instead of non-rechargeable cells. [1]

(a) two or more cells connected (together) in series allow joined / linked for connected allow more than one cell for two or more do not accept a single cell / 'a store of energy'(1)
(b) B (two different metals in an electrolyte)(1)
(c) an (external) electric current is passed through the cell / it is connected to a power supply / charger allow electricity is supplied to it(1)
(c) (which) reverses the chemical reactions allow turns the products back into the reactants ignore 'puts the energy back' unqualified(1)
(d) one from: fewer cells are thrown away / less waste / less landfill; fewer (raw) materials / resources used to make new cells; less energy used to manufacture new cells ignore cheaper(1)
Answer: (a) two or more cells in series; (b) B; (c) external current passed through it, reversing the reactions; (d) fewer cells thrown away / fewer resources used
Examiner tip: In (b) a cell needs two different metals: identical electrodes give no voltage, so A and C are wrong.

4Grade 4–5Triple only4 marks

The diagram shows a hydrogen fuel cell connected to a lamp.

(a) Name the gas in the air that reacts in the fuel cell. [1]

(b) Name substance Z. [1]

(c) The lamp stays lit for as long as hydrogen and air are supplied. A lamp connected to an alkaline battery eventually goes out.

Explain the difference. [2]

(a) oxygen allow O₂ do not accept O / air(1)
(b) water allow H₂O / steam / water vapour(1)
(c) (in a fuel cell) the fuel / hydrogen (and oxygen) is supplied continuously / from outside the cell allow fuel cell can be refuelled(1)
(c) (in an alkaline battery) the reactants are stored inside the cell and (one of them) gets used up allow the chemicals in the battery run out(1)
Answer: (a) oxygen; (b) water; (c) fuel cell has fuel supplied from outside continuously, whereas the battery's reactants are inside it and get used up
Examiner tip: For (c) say what happens in BOTH devices: 'the battery runs out' alone only earns one mark.

5Grade 6–7Triple only5 marks

A student made simple cells using a copper electrode and an electrode of a different metal, both dipped in the same electrolyte. The table shows the results.

Metal used with copper	Voltage in V
lead	0.47
magnesium	2.71
iron	0.78
nickel	0.59
zinc	1.10

All of the metals in the table are more reactive than copper.

(a) Use the results to put the five metals in order of reactivity, starting with the most reactive. [2]

(b) Describe the pattern linking the voltage of a cell to the metals used. [1]

Predict the voltage of this cell. Show how you worked out your answer. [2]

(a) magnesium, zinc, iron, nickel, lead – all five in the correct order(1)
(a) allow 1 mark (instead of 2) if one adjacent pair is swapped, or if the order is fully reversed (least reactive first)(1)
(b) the bigger the difference in reactivity between the two metals, the bigger the voltage allow the more reactive the other metal (compared with copper) the greater the voltage(1)
(c) $1.10 - 0.78$ allow difference between the zinc and iron voltages(1)
(c) 0.32 (V) allow 0.3 (V) allow ECF from an incorrect subtraction(1)
Answer: (a) Mg > Zn > Fe > Ni > Pb; (b) larger difference in reactivity → larger voltage; (c) 1.10 − 0.78 = 0.32 V
Examiner tip: In (c), both cells share copper, so the zinc–iron voltage is the difference between the two readings — don't add them.

6Grade 4–5Triple only5 marks

A student investigated how the type of electrolyte affects the voltage of a cell. She used a zinc electrode and a copper electrode each time and measured the voltage three times for each electrolyte.

Electrolyte	Voltage in V			Mean voltage in V
Electrolyte	Test 1	Test 2	Test 3	Mean voltage in V
sodium chloride solution	0.92	0.94	0.93	0.93
dilute sulfuric acid	1.02	0.99	1.02	1.01
copper sulfate solution	1.08	1.10	0.85	X
lemon juice	0.89	0.91	0.90	0.90

(a) What is the independent variable in this investigation? [1]

(b) Give two variables the student should keep the same. [2]

(a) (type of) electrolyte do not accept voltage / metals(1)
(b) any two from: the (two) metals / electrodes used (zinc and copper); concentration of the electrolyte; volume of electrolyte; temperature; distance between the electrodes; size / surface area of electrodes (in the electrolyte) / depth electrodes are dipped ignore 'same equipment' / 'same voltmeter' / 'amount' unqualified(1)
(b) second variable from the list above(1)
(c) 0.85 identified as anomalous and not used allow $\dfrac{1.08 + 1.10}{2}$(1)
(c) 1.09 (V) a correct answer scores 2 marks allow 1 mark only for 1.01 (anomaly included)(1)
Answer: (a) type of electrolyte; (b) e.g. metals used, concentration of electrolyte; (c) X = (1.08 + 1.10) ÷ 2 = 1.09 V
Examiner tip: Spot the anomaly before averaging: including 0.85 V gives 1.01 V and loses a mark.

7Grade 8–9HigherTriple only6 marks

Some hydrogen fuel cells use potassium hydroxide solution as the electrolyte.

(a) The half equation at the negative electrode is:

$$\text{H}_2 + \ldots\,\text{OH}^- \rightarrow \ldots\,\text{H}_2\text{O} + \ldots\,\text{e}^-$$

Balance the half equation. [1]

(b) Complete the half equation at the positive electrode. [1]

$$\text{O}_2 + 2\text{H}_2\text{O} + \ldots\ldots \rightarrow 4\text{OH}^-$$

(d) Use your two half equations to show that the overall reaction is $2\text{H}_2 + \text{O}_2 \rightarrow 2\text{H}_2\text{O}$ [2]

(a) $\text{H}_2 + 2\text{OH}^- \rightarrow 2\text{H}_2\text{O} + 2\text{e}^-$ – all three numbers correct allow correct multiples(1)
(b) $4\text{e}^-$ allow 4e(1)
(c) hydrogen (molecules) lose electrons so hydrogen is oxidised(1)
(c) oxygen (molecules) gain electrons so oxygen is reduced allow 1 mark for 'hydrogen oxidised and oxygen reduced' with no reference to electrons(1)
(d) negative-electrode equation multiplied by 2 (so both equations involve 4 electrons): $2\text{H}_2 + 4\text{OH}^- \rightarrow 4\text{H}_2\text{O} + 4\text{e}^-$(1)
(d) equations added and $4\text{e}^-$, $4\text{OH}^-$ and $2\text{H}_2\text{O}$ cancelled from both sides to leave $2\text{H}_2 + \text{O}_2 \rightarrow 2\text{H}_2\text{O}$(1)
Answer: (a) H₂ + 2OH⁻ → 2H₂O + 2e⁻; (b) 4e⁻; (c) hydrogen loses electrons (oxidised), oxygen gains electrons (reduced); (d) double (a), add to (b), cancel 4e⁻, 4OH⁻ and 2H₂O
Examiner tip: Check charge as well as atoms: in (a) the left side has charge 2− so 2 electrons must appear on the right.

8Grade 4–5Triple only5 marks

The graph shows how the voltage of one alkaline cell changes while it powers a torch.

(a) Two of these cells are connected in series to make a battery. What is the voltage of the battery at the start? [1]

(b) (i) Use the graph to find the voltage of the cell after 6 hours. [1]

(ii) The torch stops working when the voltage of the cell falls below 1.0 V. Use the graph to find how long the torch works for. [1]

Calculate how many rechargeable cells must be connected in series to give the same voltage. [2]

(a) 3.1 (V) allow 3.0–3.2 (V) allow 2 × the value read from the graph at time 0(1)
(b)(i) 1.25 (V) allow 1.24–1.26 (V)(1)
(b)(ii) 9 (hours) allow 8.8–9.2 (hours)(1)
(c) $6.0 \div 1.2$(1)
(c) 5 (cells) a correct answer scores 2 marks(1)
Answer: (a) 3.1 V; (b)(i) 1.25 V; (b)(ii) 9 hours; (c) 6.0 ÷ 1.2 = 5 cells
Examiner tip: Cells in series ADD their voltages — double the single-cell reading in (a), don't just read the graph.

9Grade 6–7HigherTriple only5 marks

A bus is powered by hydrogen fuel cells. On one day the bus uses 24 kg of hydrogen.

The overall reaction in the fuel cell is:

$$2\text{H}_2 + \text{O}_2 \rightarrow 2\text{H}_2\text{O}$$

Relative atomic masses ($A_r$): H = 1 O = 16

(a) Calculate the mass of water produced, in kg. [3]

(b) Calculate the volume of oxygen, in dm³, that reacts with the hydrogen.

The volume of one mole of any gas at room temperature and pressure is 24 dm³. [2]

(a) moles of hydrogen $= 24\,000 \div 2 = 12\,000$ (mol)(1)
(a) moles of water = 12 000 (mol) (1 : 1 ratio) and $M_r$ of water = 18(1)
(a) 216 (kg) allow 216 000 g allow alternative method: 4 g H₂ → 36 g H₂O so 24 kg → 24 × 36 ÷ 4 a correct answer scores 3 marks(1)
(b) moles of oxygen $= 12\,000 \div 2 = 6000$ (mol) allow ECF from (a)(1)
(b) volume $= 6000 \times 24 = 144\,000$ (dm³) allow 1.44 × 10⁵ (dm³) a correct answer scores 2 marks(1)
Answer: (a) 216 kg; (b) 144 000 dm³
Examiner tip: Convert kg to g before using moles (24 kg = 24 000 g), then convert back — and remember 2 mol H₂ need only 1 mol O₂.

10Grade 6–7Triple only6 marks

A delivery company is choosing between vans powered by hydrogen fuel cells and vans powered by rechargeable lithium-ion batteries. The table gives information about the two vans.

	Hydrogen fuel cell van	Battery van
Distance travelled on a full tank / full charge in km	500	250
Time to refuel / fully recharge	5 minutes	8 hours
Mass of fuel cell system or battery in kg	150	550
Cost of van in £	68 000	42 000
Approximate number of refuelling / charging points in the UK	20	70 000
Waste product when the van is driven	water	none

Evaluate the use of hydrogen fuel cells compared with rechargeable batteries for the company's delivery vans.

Use the information in the table and your own knowledge. [6]

Fuel cell: travels twice as far (500 km vs 250 km) before refuelling – fewer stops on long routes(1)
Fuel cell: refuels in minutes rather than hours, so vans spend less time out of use(1)
Fuel cell: lighter (150 kg vs 550 kg), so the van can carry a bigger load / uses less energy(1)
Fuel cell: only product is water, so no CO₂ / pollutants released from the van(1)
Fuel cell: hydrogen is a flammable gas – hard to store, needs high pressure / large tanks(1)
Fuel cell: hydrogen is mostly made from fossil fuels (e.g. methane) or by electrolysis that uses a lot of electricity, which may come from fossil fuels(1)
Fuel cell: very few refuelling points (20) and the van costs £26 000 more(1)
Battery: cheaper van and far more charging points (70 000), so easier to recharge near depots(1)
Battery: long recharge time / shorter range, so may need extra vans or charging during the day(1)
Battery: electricity used to charge may be generated from fossil fuels; batteries can only be recharged a limited number of times and contain chemicals that are toxic / hard to dispose of(1)
Conclusion: a justified judgement, e.g. battery vans better for short local deliveries near depots; fuel cell vans better for long routes only if hydrogen supply and refuelling points improve(1)

Level	Marks	What it looks like
Level 3	5–6	A detailed evaluation that compares the two vans across several factors, using data from the table and own knowledge (e.g. how hydrogen is produced, storage, charging electricity source). Advantages and disadvantages of both are weighed and a justified conclusion is reached.
Level 2	3–4	Several relevant points about both types of van, some linked to data in the table, with some comparison. A conclusion may be given but is not fully supported.
Level 1	1–2	Simple statements about one or both vans, possibly copied from the table, with little or no comparison or explanation.
No relevant content	0	Nothing worthy of credit.

Answer: Levels-marked evaluation: weigh range, refuel time, mass, cost, refuelling infrastructure and environmental impact of both, then give a justified conclusion.
Examiner tip: Top-level answers USE the numbers (e.g. 'twice the range') and finish with a judgement backed by a reason — listing facts with no conclusion caps you at Level 2.

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