Chemical Cells & Fuel Cells Practice Questions

Question 1

3 marks

A hydrogen–oxygen fuel cell is used to supply electricity to the instruments on a spacecraft.

(a)

Which substance is the only product of the reaction in a hydrogen–oxygen fuel cell?

Tick one box.

A carbon dioxide
B hydrogen peroxide
C oxygen
D water

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(b)

The fuel cell produces a voltage for the whole of a 10-day mission. A chemical cell of the same mass would have stopped producing a voltage before the end of the mission.

Explain why.

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Question 2

4 marks

A student sets up the chemical cell shown below, using a strip of magnesium and a strip of copper in sodium chloride solution.

(a)

The student first tried using pure water instead of sodium chloride solution and the voltmeter read $0\ \mathrm{V}$ .

Give one reason why sodium chloride solution must be used.

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(b)

The student replaces the magnesium strip with a strip of zinc. Zinc is less reactive than magnesium.

State and explain what happens to the reading on the voltmeter.

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(c)

The cell is left connected overnight. Give one reason why the voltmeter reads $0\ \mathrm{V}$ the next morning.

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Question 0

5 marks

A group of students made a number of chemical cells. In each cell, one electrode was a strip of copper and the other electrode was a strip of a different metal. The same sodium chloride solution was used each time.

The table shows their results.

Metal used with copper	Voltage in V
magnesium	2.71
zinc	1.10
iron	0.78
copper	0.00

(a)

Explain why the voltage is $0.00\ \mathrm{V}$ when both electrodes are made of copper.

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(b)

Lead is less reactive than iron but more reactive than copper.

Predict the voltage of a cell made from lead and copper in sodium chloride solution. Justify your answer.

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(c)

The students left the magnesium–copper cell connected to a voltmeter for two days. Describe and explain how the reading changed during this time.

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Question 0

4 marks

In one design of hydrogen–oxygen fuel cell, the two electrodes are thin layers of platinum. The electrolyte between them is an acidic polymer that allows $\mathrm{H^+}$ ions to pass through it.

(a)

Hydrogen is oxidised at the negative electrode.

Complete the half equation for this reaction.

$\mathrm{H_2} \rightarrow \text{.............................}\ \mathrm{H^+} + \text{.............................}$

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(b)

Suggest two reasons why platinum is used for the electrodes rather than a metal such as zinc.

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Question 0

5 marks

A company that owns a large indoor warehouse must choose how to power its forklift trucks. The trucks can be powered either by hydrogen–oxygen fuel cells or by rechargeable chemical cells.

The table gives some information about the two options.

	Hydrogen–oxygen fuel cell	Rechargeable chemical cell
Time to refuel or recharge	3 minutes	8 hours
Operating time from one refuel or recharge	8 hours	5 hours
Mass of the power unit	90 kg	330 kg
Cost to fit to one truck	£20 000	£8 000
Substances released inside the warehouse	water vapour only	none
Voltage during use	constant while fuel is supplied	falls as the cell discharges

(a)

Use the table to give one advantage of using fuel cells to power the forklift trucks.

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(b)

Evaluate the use of hydrogen–oxygen fuel cells, rather than rechargeable chemical cells, to power the forklift trucks in this warehouse.

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Question 0

6 marks

Some spacecraft use a hydrogen–oxygen fuel cell that contains an alkaline electrolyte. This electrolyte allows hydroxide ions, $\mathrm{OH^-}$ , to move through it.

The half equations for the reactions at the two electrodes are:

negative electrode: $\mathrm{H_2} + 2\mathrm{OH^-} \rightarrow 2\mathrm{H_2O} + 2\mathrm{e^-}$

positive electrode: $\mathrm{O_2} + 2\mathrm{H_2O} + 4\mathrm{e^-} \rightarrow 4\mathrm{OH^-}$

(a)

Use the two half equations to show that the overall equation for the reaction in this fuel cell is

$2\mathrm{H_2} + \mathrm{O_2} \rightarrow 2\mathrm{H_2O}$

Show your working.

/ 3

(b)

Explain, in terms of electrons, why this fuel cell produces a voltage, and why the voltage does not fall to zero while the spacecraft's tanks still contain hydrogen and oxygen.

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Atomic Structure

States of Matter & Mixtures

Chemical changes

Extracting metals & equilibria

Separate Chemistry 1

Groups in the periodic table

Rates of reaction & energy changes

Fuels & Earth science

Separate Chemistry 2

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Question 2

Question 0

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