AQA GCSE Chemistry: Combined Science

Topic Questions

4.3 Electrolysis

1a4 marks

This question is about electrolysis.

Draw one line from the electrolysis keyword to the correct definition.

electrolysis-keyword-match
1b3 marks

Ionic compounds are capable of being electrolysed under certain conditions.

Complete the sentences about the electrolysis of ionic compounds.

Choose answers from the box.

aqueous liquid solid
no free electrons no free ions


Ionic compounds cannot conduct electricity when they are __________________ .

This is because they have __________________ that can move and carry charge.

To conduct electricity, an ionic compound must be __________________ or dissolved in solution.

1c2 marks
Draw a ring around the correct answer to complete the sentences about the movement of ions.
 
Positive ions move towards the

anode

cathode

electrode

Negative ions move towards the

anode

cathode

electrode

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2a1 mark

This question is about the electrolysis of zinc chloride.

Figure 1 shows the apparatus for the electrolysis of molten zinc chloride.

Figure 1

4-3-electrolysis-of-solid-compound
Why can electrolysis not be performed using the apparatus as shown in Figure 1?

2b2 marks

Chloride ions move towards the positive electrode.

Explain why chloride ions move towards the positive electrode.

2c1 mark

Name the product formed at the negative electrode.

2d2 marks

Explain the type of reaction that occurs at the negative electrode.

Type of reaction: _______________________________________

Explanation: __________________________________________

2e2 marks

One of the products from the electrolysis of zinc chloride is chlorine.

Balance the half equation to show the formation of chlorine. 

____ Cl → Cl2 + ____ e 

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3a2 marks

This question is about methods of extraction.

The method that is used to extract a metal from its ore can be determined by the position of the metal in the reactivity series.

Table 1 contains a section of the reactivity series.

Table 1

More reactive metal / element
Potassium
Calcium
Aluminium
Carbon
Zinc
Iron
Copper
Platinum
Less reactive metal / element


Draw a ring around the correct answer to complete the sentences about metal extraction.

Displacement by carbon is used to extract

calcium

iron

platinum

Electrolysis is used to extract

calcium

iron

platinum

3b1 mark

Aluminium is extracted from aluminium oxide using an electrolytic cell as shown in Figure 1.

Figure 1

aqa-gcse-sq-4-3e-3b-aluminium-extraction

Aluminium oxide consists of Al3+ ions and O2– ions.

What is the chemical formula of aluminum oxide?

3c1 mark

Aluminium oxide is mixed with cryolite and melted before electrolysis takes place.

Why is the aluminium oxide mixed with cryolite?

Tick () one box. 

To obtain more aluminium  
To increase the melting point of the mixture  
To decrease the melting point of the mixture  
To use less aluminium oxide  
3d1 mark

What is produced at the positive electrode?

3e3 marks

The positive carbon electrode has to be replaced periodically.

Explain why the positive electrode needs to be replaced. Your answer should include an equation.

The positive carbon electrode needs to be replaced because ____________________

Equation: ________ + ________ → ________

3f1 mark

Complete the half equation to show the formation of aluminium.

Al3+ + _____ → Al

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4a2 marks

This question is about electrolysis.

A student investigates the electrolysis of different salt solutions, using the equipment shown in Figure 1. 

Figure 1 

aqa-gcse-sq-4-3e-4a-electrolysis---general-salt

What observations could be made if a metal is produced at one of the electrodes?

Observation 1: ________________________________________

Observation 2: ________________________________________

4b1 mark

Which electrode will non-metal ions such as the chloride (Cl) and sulfate (SO42–) ion be attracted to?

4c1 mark

An aqueous solution of copper (II) chloride is electrolysed.

Which ion is not present during this reaction?

Circle one ion.

Cu2+ H H+ OH Cl
4d4 marks

The student investigates the electrolysis of:

  • Copper (II) chloride solution
  • Sodium sulfate solution

Table 1 contains a section of the reactivity series.

Table 1

More reactive metal / element
Potassium
Sodium
Aluminium
Carbon
Zinc
Iron
Hydrogen
Copper
Less reactive metal / element


Complete Table 2 to predict the products.

Choose answers from the box.

chlorine bromine hydrogen oxygen copper sodium


Table 2

Substance electrolysed

Product at cathode

(negative electrode)

Product at anode

(positive electrode)

Copper (II) chloride solution

 

 

Sodium sulfate solution

 

 

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5a2 marks

This question is about the electrolysis of molten and aqueous sodium chloride.

Complete the word equation to show the products of the electrolysis of molten sodium chloride.

Sodium chloride → _______________ + _______________

5b2 marks

The electrolysis of aqueous sodium chloride produces hydrogen gas.

Balance the half equation to show the formation of hydrogen gas.

____ H+ + ____ → H2 

5c2 marks

Chlorine is formed during the electrolysis of sodium chloride solution.

2Cl → Cl2 + 2e 

What type of reaction this is?

Draw a ring around the correct words to complete the sentences.

The formation of chlorine from chloride ions is 

a decomposition

a neutralisation

an oxidation

a reduction

reaction

This reaction happens 

at the positive anode

at the negative cathode

at the negative anode

at the positive cathode

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1a2 marks

This question is about electrolysis.

A student investigated the electrolysis of copper chromate solution.

Chromate ions, CrO subscript 4 superscript 2 minus end superscript, are yellow.

Explain the colour of copper chromate solution.

1b3 marks

The student's apparatus to electrolyse copper chromate solution using zinc electrodes is shown in Figure 1.

Figure 1

aqa-gcse-4-3h-sq-q1b-copper-chromate-electrolysis

Explain why the negative electrode increases in mass.

1c2 marks

The student replaces the zinc electrodes with carbon electrodes.

Explain why the mass of one of the electrodes decreases.

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2a1 mark

This question is about the electrolysis of aluminium oxide.

Explain why aluminium is extracted from its ore by electrolysis.

2b2 marks

Explain why cryolite is used in the extraction of aluminium.

2c2 marks

Aluminium oxide undergoes a redox reaction during electrolysis.

Explain whether aluminium is produced as the result of a reduction or an oxidation reaction.

Your answer should include an appropriate equation including state symbols.

2d3 marks

Explain what happens to the anode during the electrolysis of aluminium oxide.

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3a1 mark

This question is about the electrolysis of zinc (II) chloride, ZnCl2.

Zinc (II) chloride can conduct electricity when it is molten or dissolved in solution.

Explain why zinc (II) chloride cannot conduct electricity when it is solid. 

3b3 marks

In terms of structure and bonding, explain why graphite is commonly used as the electrode in electrolysis reactions.

3c3 marks

Explain how the product at each electrode is formed during the electrolysis of molten zinc chloride.

3d2 marks

The electrolysis of molten zinc chloride gives different products compared to the electrolysis of aqueous zinc chloride.

Explain any differences in the products from each electrolysis experiment.

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4a4 marks

This question is about sodium chloride.

Describe, in terms of electrons and with the help of suitable equations, what happens during the electrolysis of molten sodium chloride.

4b2 marks

The products of electrolysis of molten sodium chloride are different to those of aqueous sodium chloride.

Explain the different products from the electrolysis of aqueous sodium chloride.

4c3 marks

Nuclear submarines can stay underwater for months without needing to come to the surface.

Oxygen for the crew to breathe is produced using a piece of equipment called an automated electrolytic oxygen generator.

Many people assume that seawater is electrolysed to produce the oxygen, this assumption is incorrect. 

Explain why the assumption is not only incorrect but potentially hazardous and how the oxygen can be produced by electrolysis.

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5a2 marks

This question is about the electrolysis of sulfuric acid.

A student investigated how the volume of gases produced changes with time in the electrolysis of dilute sulfuric acid.

The apparatus is shown in Figure 1.

Figure 1

aqa-gcse-4-3h-sq-q5a-dil-sulfuric-acid-electrolysis

The student has made an error in the apparatus. 

Explain how the apparatus should be changed.

5b4 marks

With the help of suitable equations, explain why it is more likely that the hydrogen formed in this electrolysis comes from the sulfuric acid than water.

5c2 marks

Sulfate ions and hydroxide ions are both attracted to the anode.

Hydroxide ions are less stable than sulfate ions so they are discharged at the anode.

OH (aq) → OH (aq) + e 

The OH groups produced exist for a fraction of a second before they form water and oxygen.

Write a balanced symbol equation, including state symbols, for this reaction.

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1a4 marks

Magnesium chloride is an ionic compound that can be electrolysed. 

Figure 1 shows two experiments in which MgCl2 undergoes this process.

Figure 1 

aqa-gcse-sq-4-3m-q1a-magnesium-chloride-electrolysis-melt--aq

Explain why solid magnesium chloride cannot be electrolysed and give the necessary conditions for electrolysis to occur.

1b4 marks

Justify the production of magnesium metal at the cathode in Experiment A.

1c1 mark

Identify the gas produced at the cathode in Experiment B.

1d2 marks

Explain why magnesium is not produced at the cathode in Experiment B.

1e1 mark

Balance the half equation which occurs at the anode.

________ Cl       →      Cl2 + _______

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2a3 marks

Hydrogen, chlorine and sodium hydroxide are commercially important chemicals which can all be made in one process. 

The process involves passing electricity through an aqueous solution of sodium chloride (brine). 

Figure 2 shows an electrolytic cell in which this process can be carried out.

Figure 2 

brine-electrolysis-aqa-gcse-sq-m2a

Identify the substances produced at points A, B and C.

A _________________________

B _________________________

C _________________________

2b2 marks

Complete and balance the equations for the reactions at the electrodes.

___Cl – ___e → Cl2
___H + ___e → H2

2c1 mark

Identify the compound in the cell responsible for producing the hydrogen ions.

2d1 mark

What kind of particles must be able to pass through the barrier so that electrolysis can take place?

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3a2 marks

This question is about the extraction of aluminium using electrolysis. The process is displayed in Figure 3.

Figure 3aqa-gcse-4-3m-sq-q3a-electrolysis-to-produce-aluminium

Why isn’t aluminum extracted by heating with carbon?

3b3 marks

Explain why aluminium is formed at the cathode.

3c4 marks

Explain why carbon dioxide is formed at the anode and why the anode must be continually replaced.

3d4 marks

The electrolyte in the process consists of a mixture of aluminium oxide and cryolite. 

Explain why a mixture is used instead of just the aluminium oxide.

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4a1 mark

This question is about the electrolysis of sulfuric acid. The apparatus used in this process is shown in Figure 4

Oxygen is formed at the anode.

Figure 4

aqa-gcse-4-3m-sq-q4a-hoffmann-electrolysis-of-water-h2so4

Solutions which decompose when electricity is passed through them have a specific name. 

What is the name given to these solutions?

4b2 marks

The half equation for the reaction which occurs at the anode is:

4OH → 2H2O + O2 + 4e

Describe what type of reaction this is and give a reason for your answer.

4c2 marks

Write a balanced half equation for the reaction which occurs at the cathode.

4d3 marks

As the electricity is passed through the electrolyte what happens to the concentration of the sulfuric acid? 

Explain your answer.

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5a3 marks

A student electrolysed a solution of potassium chloride with the intention of isolating potassium. 

The apparatus was set up as shown in Figure 5

Figure 5 

aqa-gcse-4-3m-q5a-potassium-chloride-cell

The student expected to see potassium metal being formed at the cathode but instead observed bubbles of gas being formed.

Name the gas produced at the cathode and explain why this gas is produced, giving a reason why potassium is not produced.

5b2 marks

The student then electrolysed molten potassium chloride instead of a solution and found that potassium metal was produced at the negative electrode.

Describe how potassium atoms are produced from ions of potassium.

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