Chemical Cells & Fuel Cells (AQA GCSE Chemistry)

A student investigated the voltage produced by simple cells using the apparatus shown in Figure 1.

Figure 1

Using different metals for the electrodes produced different voltages as shown in Table 1 below. 

Table 1

Electrode A	Electrode B	Voltage in V
Copper	Copper	0.00
Copper	Tin	0.48
Copper	Zinc	1.10
Copper	Iron	0.78
Copper	Magnesium	2.71

List the metals in the table in order of reactivity.

Most reactive   ____________________ 

____________________

____________________

____________________

Least reactive         Copper                   

Explain how you arrived at your answer to part a).

Batteries consist of electrochemical cells.

Describe how a 9.0 V battery can be made from cells of voltage 1.5 V

Non-rechargeable cells eventually stop producing electricity. 

Explain why and name a typical cell that is non-rechargeable.

Complete the word equation for the reaction which occurs in a hydrogen fuel cell.

hydrogen  +  ___________________  ⟶  water

Give two reasons why using a hydrogen fuel cell is seen as a clean source of energy using the equation in part e).

In an investigation to discover the reactivity series of some common metals, an electrochemical cell has two metal electrodes placed in an electrolyte solution.

Electrode A is copper.

Electrode B is changed to each different metal in turn and the voltage of the cell is measured. The results are shown below:

Metal of electrode B	Voltage (V)
Copper	0.00
Cobalt	+0.62
Tin	+0.48
Nickel	+0.59

Starting with the least reactive, place these metals in order of ascending reactivity.

One of the electrodes used in an electrochemical cell is a 'hydrogen electrode'.

Four different metals were used in turn as the second electrode to complete the cell. The voltage of each cell was measured and is shown below:

Metal used on the second electrode	Voltage of the cell compared to hydrogen (V)
Copper	+0.34
Silver	+0.80
Iron	-0.04
Nickel	-0.26

Which pair of metals would give the greatest voltage when used as electrodes in a different cell?

Some new models of cars are powered by hydrogen fuel cells.

What type of energy is released by these cells?

Owners of these cars must buy hydrogen from specially equipped hydrogen filling stations. 

The number of these stations in the UK is expected to increase up to the year 2035 as can be seen in Figure 3.

Figure 3

Explain why the UK government should encourage the production of more hydrogen filling stations. 

Use the data in Figure 3 and your own knowledge to answer this question, making reference to the reaction of hydrogen fuel cells.

Give two disadvantages of using hydrogen fuel cells.

In some types of cell the chemical reaction can be reversed by applying an external current.

Which type of cell can this occur in?

Hydrogen fuel cells are often used instead of rechargeable batteries in spacecraft.

Which of the following is not an advantage of using hydrogen fuel cells in spacecraft?

Electrochemical cells contain chemicals which react together.   

This reaction involves the movement of electrons which is what produces electricity.

Rechargeable cells are cells that can be recharged. 

Explain how this process occurs.

Give three factors that affect the voltage produced by a cell.

Balance the half-equation for the reaction which occurs at an electrode in one kind of hydrogen fuel cell.

H₂   +  OH⁻  ⟶  H₂O   +  e⁻

Explain why the fuel cell in part (c) can be described as an alkaline fuel cell?

Some chemical reactions can produce electricity. 

Figure 1 shows a simple cell.

Figure 1

Electrode A	Electrode B	Electrolyte	Tick (✓) one box.
Zinc	Zinc	Sodium chloride solution
Iron	Iron	Water
Copper	Zinc	Sodium chloride solution
Zinc	Copper	Water

 

Alkaline batteries are non-rechargeable.

Explain why they cannot be recharged.

Rechargeable lithium-ion batteries and hydrogen fuel cells can be used to power electric cars.

Complete the balanced equation for the overall reaction in a hydrogen fuel cell and state what type of reaction it is.

________ H₂ + ________ ⟶ ________ H₂O

Table 2 below shows data based on different methods of powering electric cars.

Table 2

	Hydrogen fuel cell	Rechargeable lithium-ion battery
Time to refuel or recharge in minutes	4	30
Distance car can travel per unit of energy in km	25	68
Distance car can travel before refuelling or recharging in miles	Up to 420	Up to 230
Minimum cost of car in £	55,000	16,000
Cost of refuelling or recharging in £	60	5

Use the table and your knowledge to evaluate the use of hydrogen fuel cells compared with rechargeable lithium-ion batteries to power electric cars.

In a hydrogen fuel cell, the reaction between hydrogen and oxygen produces electrical energy. The equation for the reaction is:

2H₂   +   O₂   →   2H₂O

Hydrogen fuel cells can be used to power some cars.

Reactions happen at both the positive electrode and the negative electrode in the fuel cell.

Write the two half equations that occur at each electrode and state with reason what kind of reaction each one is.

The energy required for a car powered by a hydrogen fuel cell to travel 400 km is 232 MJ.

The energy that is released when 1 mole of hydrogen gas reacts with oxygen is 290 kJ.

The volume of 1 mole of a gas at room temperature and pressure is 24 dm³.

Calculate the volume of hydrogen gas, in dm³, at room temperature and pressure needed for the car to travel 250 km.

The volume of hydrogen gas that would be required to allow a car to travel a reasonable distance between refuelling would be greater than the volume of a tank that could fit in a car.

Suggest one way in which this volume can be decreased.

Methanol can be used as the fuel in a fuel cell instead of hydrogen.

The chemical equation for is:

2CH₃OH + 3O₂ → 2CO₂ + 4H₂O

The equation for the reaction can be also be shown as:

Table 1 shows the bond energies of different bonds.

Table 1

Bond	Bond energy in kJ/mol
C-H	412
O-H	464
C=O	805
C-O	360

The overall energy change for the reaction is -1318 kJ/mol.

Use the bond energies in Table 1 and the overall energy change to calculate the bond energy of the O=O bond in kJ/mol. 

A student investigated how the metal used as the electrode in a simple cell affected the voltage produced. They used the apparatus shown in Figure 1.

Figure 1

The student's results are shown in Table 1.

Table 1

Metal used as Metal 2	Voltage produced in volts
Chromium	1.2
Iron	0.5
Magnesium	1.8
Nickel	1.0
Silver	-0.6
Zinc	0.3

Which metal is the most reactive?

Explain your answer.

Why does silver have a negative voltage?

The half equation for the reaction that happens at the copper electrode in the simple cell made using copper and magnesium electrodes is:

Cu²⁺ + 2e^- → Cu

Give the half equation for the reaction that occurs at the magnesium electrode and state whether this is oxidation or reduction, giving a reason why.

Predict the voltage that would be produced if the simple cell was made with zinc and nickel electrodes.

A simple cell consists of two different metals in contact with an electrolyte.

Explain what a battery is.

Batteries can be non-rechargeable and rechargeable.

Explain the difference between the two different types of batteries. 

A student  made a battery from lemons as shown in Figure 1.

Figure 1

The student found that if they had less than four lemon halves connected as shown in Figure 1, the bulb did not turn on.

Explain why.

The student changed the bulb for a voltmeter so that they could measure the voltage produced.

They investigated what happened to the voltage produced by the battery when different metals were used instead of copper and zinc.

Give two control variables in this investigation.

The results that the student obtained are shown in Table 1.

Table 1

The results give a positive voltage when metal 1 is more reactive than metal 2.

The results give a negative voltage when metal 2 is more reactive than metal 1.

List the metal in order of reactivity, starting with the least reactive metal.

Predict the voltage that would have been obtained for the reading that was not taken where metal 1 is iron and metal 2 is aluminium.

Explain your answer.

Hydrogen fuel cells can be constructed using either an acidic or alkaline electrolyte.

The half equations at the electrodes in acidic conditions are:

• H₂ ⟶ 2 H⁺ + 2 e^-
• O₂ + 4 H⁺ + 4 e^- ⟶ 2 H₂O

The half equations at the electrodes in alkaline conditions are:

• H₂ + 2 OH^- ⟶ 2 H₂O + 2 e^-
• O₂ + 2 H₂O + 4 e^- ⟶ 4 OH^-

The overall equation for the reaction in alkaline conditions is:

• 2H₂ + O₂ → 2H₂O

Suggest why the voltage produced in a hydrogen fuel cell with an acidic electrolyte is exactly the same as one with an alkaline electrolyte.

You should refer to the overall equation for the reactions in your answer.

The electrodes used in hydrogen fuel cells can be made by using a porous ceramic material which has been coated in platinum.

Suggest two reasons why this method of making electrodes is preferential to using platinum rods as electrodes.

The only product formed in hydrogen fuel cells is water so they are often thought of as sustainable.

Suggest a reason why this is not necessarily true.

Other than any factors which may make fuel cells less sustainable, give two disadvantages of using hydrogen fuel cells compared with rechargeable battery, such as a lithium-ion battery, when used to power an electric car?