Electrolytic Processes (Edexcel GCSE Chemistry)

Exam Questions

2 hours22 questions
1a1 mark

Two compounds of barium are barium sulfide and barium chloride.

The hazard symbol shown in Figure 5 is on bottles containing barium metal.


fig-5-q5a-1cho-1f-paper-1-june-2018
Figure 5

State the meaning of this hazard symbol.

1b1 mark

Give the names of the elements combined in barium sulfide.

1c2 marks

Barium chloride is toxic.

Explain one safety precaution that should be taken when using barium chloride.

1d2 marks
i)
A beaker of barium chloride solution and a beaker of dilute sulfuric acid were placed on a balance, as shown in Figure 6.

fig-6-qdi-1cho-1f-paper-1-june-2018

Figure 6

The total mass reading on the balance was 25.7 g.

The dilute sulfuric acid was poured into the barium chloride solution and the beaker replaced on the balance, as shown in Figure 7.

figure-7

Figure 7

The mixture formed contained a white precipitate.

State the total mass reading on the balance after the reaction.

(1)

ii)
Give the name of the white precipitate formed by the reaction of barium chloride solution with dilute sulfuric acid.
(1)
1e4 marks

Solid sodium chloride is dissolved in water.

The sodium chloride solution is electrolysed in the apparatus shown in Figure 8.

fig-8-q5e-1cho-1f-paper-1-june-2018

Figure 8

i)
State why sodium chloride solution, rather than solid sodium chloride, must be used in this experiment.

(1)

ii)
The formulae of the ions present in the sodium chloride solution are

Na to the power of plus                begin mathsize 14px style CI to the power of minus end style                 straight H to the power of plus                    OH to the power of minus

Circle the ions that would be attracted to the anode.

(1)

iii)
Molten lead bromide can be electrolysed to form molten lead and bromine gas.

Explain how a student could modify the apparatus shown in Figure 8 to carry out this electrolysis.

(2)

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2a4 marks

This question is about electrolysis.

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

 
MbFGvzwH_match-up-electrolysis-key-terms
 
2b3 marks

Ionic compounds are capable of being electrolysed under certain conditions.

Use words from the box to complete the sentences.

 
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.

 
2c2 marks

Place ticks in boxes by the two statements that are correct.

 Positive ions move towards the negative electrode   
 Negative ions move towards the cathode   
 Negative ions remain in solution  
 Positive ions move towards the anode  
 Negative ions move towards the anode  
2d1 mark

Name the two products formed when molten lead bromide undergoes electrolysis.

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3a1 mark

Figure 1 shows the apparatus used for the electrolysis of copper sulfate solution using copper electrodes.

edx-3-2e-q3a-electrolysis-apparatus

Figure 1

Complete the statement to describe electrolysis.

Electrolysis is the splitting up of compounds using ……………..

3b1 mark

What is another name for the copper sulfate solution in this experiment?

A Electric
B Electrolyte
C Electrode
D Electron
3c2 marks

One of the negative ions in the copper(II) sulfate solution are hydroxide (OH-) ions.

i)
Where do the hydroxide ions come from?

[1]

ii)
Name the other negative ion in the copper(II) sulfate solution.

[1]

3d1 mark

The mass of the negative electrode increases.

Which statement explains why?

A Copper atoms are attracted to the anode
B Copper ions are attracted to the anode
C Copper atoms are attracted to the cathode
D Copper ions are attracted to the cathode

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4a1 mark

Molten lead(II) bromide can be electrolysed using the apparatus shown in Figure 1.

edx-3-2e-q4a-lead-bromide-electrolysis-apparatus

Figure 1

Name the electrolyte in Figure 1.

4b1 mark

What is the name of the positive electrode?

A Anion
B Anode
C Cation
D Cathode
4c1 mark

Name the product that forms at the negative electrode.

4d1 mark

Predict the products formed when molten sodium chloride is electrolysed.

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5a1 mark

Water has the formula H2O.
It can be split apart into its elements using electrolysis.

Figure 1 shows the apparatus used to do this.

edx-3-2e-q5a-water-electrolysis-apparatus

Figure 1

Give another name for the negative electrode.

5b
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1 mark

Water splits to form H+ and OH- ions.

Which row correctly names these ions?

 

 

H+ ion OH- ion
A Hydrate Oxide
B Hydrate Hydroxide
C Hydrogen Hydroxide
D Hydrogen Oxide
5c1 mark

Describe why hydrogen gas is formed at the negative electrode.

5d1 mark

Use the formula of water to explain why the gases formed are hydrogen and oxygen.

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1a4 marks

An electrolysis experiment is carried out on different solutions, J, K and L.

Electricity is passed through each solution as shown in Figure 3.

fig-3-q4-1cho-1f-specimen-2018

Figure 3


Any products formed at the electrodes are identified.

The results are given in Figure 4.

solution solution conducts electricity product at cathode product at anode
J yes copper chlorine
K no none none
L yes hydrogen chlorine

Figure 4

i)
State an improvement that can be made to the circuit to show that a current is flowing during the electrolysis.

(1)


Some of these solutions are electrolytes.

ii)
State what is meant by the term electrolyte.

(2)

iii)
Which of J, K and L are electrolytes?
(1)
  A K only
  B J and L only
  C K and L only
  D J, K and L

1b
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2 marks

Copper sulfate solution was electrolysed for five minutes using copper electrodes.


Figure 5 shows the mass of the anode and of the cathode before electrolysis and after electrolysis.

  anode cathode
mass of electrode
before electrolysis / g
1.16 1.28
mass of electrode
after electrolysis / g
0.85 1.57

Figure 5

Calculate the mass of copper deposited.

mass of copper deposited = ............................................................... g

1c2 marks

Identify the products formed at the anode and cathode when molten potassium iodide is electrolysed.

Anode ...................................
Cathode ................................

1d
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2 marks

In a different electrolysis, molten sodium fluoride is decomposed.

2NaF → 2Na + F2

(relative atomic masses: F = 19, Na = 23)
(relative formula mass NaF = 42)
Calculate the maximum mass of sodium that could be formed from 168g of sodium fluoride.

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21 mark

Molten zinc bromide is electrolysed. 

The products of this electrolysis are 

  A Zinc and oxygen
  B Zinc and bromine
  C Hydrogen and bromine
  D Hydrogen and oxygen

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31 mark

During the the electrolysis of copper sulfate solution, copper ions move to the negative electrode.

What is the reason for this?

  A Copper is less reactive than hydrogen and consists of negatively charged ions
  B Copper is more reactive than hydrogen and consists of negatively charged ions
  C Copper is less reactive than hydrogen and consists of positively charged ions
  D Copper is more reactive than hydrogen and consists of positively charged ions

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41 mark

Higher Only

When copper(II) sulfate undergoes electrolysis, it produces oxygen gas at the positive electrode.

The unbalanced half equation below represents the reaction that occurs at the positive electrode.

Which numbers will correctly balance the half equation?

___ OH-    →    O2   +   ___ H2O  +  ___ e-

  A 2, 2, 2
  B 2, 4, 2
  C 4, 2, 4
  D 4, 4, 2

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51 mark

Electrolysis can be used to separate molten lead bromide. 

Which statement is true for what happens at the negative electrode?

  A Lead atoms are oxidised 
  B Lead atoms are reduced 
  C Lead ions are oxidised 
  D Lead ions are reduced 

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6a3 marks

Water, acidified with sulfuric acid, is decomposed by electrolysis.

The water is decomposed to produce hydrogen and oxygen.

 
i)
A sample of hydrogen is mixed with air and ignited.
 
State what would happen.
 
(1)
 
ii)
Throughout the experiment the volume of hydrogen and the volume of oxygen are measured at two-minute intervals. 
 
The results are shown in Figure 9.
 
time in minutes volume of hydrogen in cm3 volume of oxygen in cm3
0 0 0
2 4 2
4 8 4
6 12 6
8 16 8
 
Figure 9
 
Describe, using the data in Figure 9, what the results show about the volumes of hydrogen and oxygen produced in this experiment.
 
(2)
6b1 mark

Molten lead bromide is electrolysed.

The products of this electrolysis are

  A hydrogen and bromine
  B hydrogen and oxygen 
  C lead and bromine
  D lead and oxygen
6c2 marks

Calcium nitrate and calcium carbonate are both ionic compounds.

Calcium nitrate mixed with water behaves as an electrolyte.
Calcium carbonate mixed with water does not behave as an electrolyte.

Explain, in terms of solubility and movement of ions, this difference in behaviour. 

6d6 marks

Impure copper can be purified using electrolysis.

 
In this electrolysis

  • the anode is made of impure copper
  • the cathode is made from pure copper
  • the electrolyte is copper sulfate solution.
 

The apparatus at the start of the experiment is shown in Figure 10. 

fig-10-q9d-1cho-1f-paper-1-june-2019

Figure 10

During the electrolysis three observations are made:

  • the sizes of both the anode and the cathode change
  • a solid appears directly beneath the anode
  • the colour of the copper sulfate solution does not change. 

Explain all three observations. 

6e2 marks

Higher Only

When molten zinc chloride is electrolysed, zinc ions, Zn2+, form zinc atoms.

Write the half equation for this reaction.

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71 mark

Sodium chloride solution can undergo electrolysis. 

What product will be formed at the negative electrode?

  A Oxygen
  B Chlorine
  C Hydrogen
  D Sodium

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81 mark

A student was investigating the electrolysis of zinc chloride. 

q5-3-2-electrolysis-of-zinc-chloride-set-up

What is the correct reason for electrolysis not working? 

  A Solid zinc chloride has been used 
  B The electrodes don't conduct electricity 
  C The power supply is not connected properly 
  D The crucible is too small to allow ions to flow 

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9a5 marks

Figure 11 shows the apparatus that can be used to electrolyse sodium sulfate solution using inert electrodes.

fig-11-q8-1cho-1f-paper-1-nov-2020

Figure 11

Hydrogen is produced at the negative electrode during electrolysis.

i)
Describe the test to show the gas is hydrogen.
(2)
ii)
What is the name of gas X that forms at the positive electrode?
(1)
  A ammonia
  B oxygen 
  C nitrogen 
  D sulfur dioxide 

iii)
State what is meant by the term electrolysis.

(2)

9b
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3 marks

The sodium sulfate solution was made by dissolving 28.4 g of sodium sulfate in water to make 250 cm3 of solution.

Calculate the concentration of this solution in g dm-3.
Give your answer to three significant figures.

concentration = ...................................... g dm-3
9c1 mark

The ions present in sodium sulfate are

   sodium Na+
   sulfate SO42-


Write the formula of sodium sulfate using this information.

9d2 marks
i)
In Figure 11, the gases given off at the electrodes are collected in test-tubes.

However, the actual volume of gases cannot be measured using these test-tubes.
Suggest what apparatus could be used in place of the test-tubes in Figure 11 to measure the volume of gases given off.
(1)
ii)
State what could be added into the circuit to show a current is flowing during electrolysis.
(1)

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101 mark

The electrolysis of copper sulfate solution using copper electrodes can be used to purify copper. 

The following equipment was set up: 

q6-3-2-electrolysis-of-copper-sulfate-solution

What changes in mass would you expect to see for each electrode? 

      Anode Cathode
  A Decrease Increase
  B Increase Decrease
  C Increase Increase
  D Decrease Decrease

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111 mark

Aqueous copper(II) sulfate solution can be electrolysed using carbon electrodes. 

Which statement is true about the reaction?

  A A pink coating is seen around the positive electrode
  B Gases are given off at both electrodes
  C The gas given off at the positive electrode can be tested with a burning splint
  D The blue colour of the solution slowly fades

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12a1 mark

This question is about electrolysis.

A sample of molten potassium bromide is electrolysed.

What are the two products formed?

  A hydrogen and oxygen
  B hydrogen and bromine 
  C potassium and oxygen
  D potassium and bromine

12b2 marks

Zinc chloride and zinc carbonate contain ions.

Zinc chloride mixed with water can be electrolysed.

Zinc carbonate mixed with water cannot be electrolysed.

Explain this difference.

12c3 marks

In the electrolysis of sodium chloride solution, bubbles of a colourless gas form at the cathode.

This gas, when mixed with air, burns with a squeaky pop.

i)
Identify this gas.

(1)

ii)
Explain how this gas is formed at the cathode.

(2)

12d5 marks

A solution of copper sulfate in a beaker is electrolysed using copper electrodes.

i)
Draw a labelled diagram to show how this experiment would be set up.

The beaker has been drawn for you.
fig-q5di-1cho-1h-paper-1-nov-2021

(2)

ii)
During the electrolysis, the anode gets smaller, the cathode gets larger and the solution remains the same shade of blue.

Give the reason for each of these observations.

(3)

the anode gets smaller ......................................................................................................................................

the cathode gets larger ......................................................................................................................................

the solution remains the same shade of blue ...............................................................................................

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1a2 marks

Electrodes are placed in three different solutions, J, K and L.

A 6V direct current source is connected to the electrodes.

Any products formed at the electrodes are identified.

The results are given in Figure 12.

solution solution conducts electricity product at cathode product at anode
J yes copper chlorine
K yes hydrogen oxygen
L no none none

Figure 12

Explain which solutions are electrolytes.

1b1 mark

Which material is most suitable to make the electrodes for the electrolysis of a dilute acid?

  A zinc
  B sulfur
  C iron
  D graphite
1c4 marks

When a solution of sodium sulfate, Na2SO4, is electrolysed, the products formed at the electrodes are hydrogen and oxygen.

Explain the formation of the products at the electrodes.

1d2 marks

Higher Only

Copper is purified by the electrolysis of copper sulfate solution using an impure copper anode and a pure copper cathode.

Write the half-equation for the formation of a copper atom from a copper ion.

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2a2 marks

Molten zinc chloride is an electrolyte.

i)
Which row shows the products formed at the anode and at the cathode when molten zinc chloride is electrolysed?
(1)
 
      product at anode product at cathode
  A oxygen zinc
  B chlorine hydrogen
  C chlorine zinc
  D oxygen hydrogen


ii)

Which of the following is the reason why molten zinc chloride is an electrolyte?
(1)
 
  A it contains molecules that can move
  B it has a giant structure
  C it contains delocalised electrons
  D it contains ions that can move
2b6 marks

Copper sulfate solution was electrolysed using copper electrodes.

i)
Draw a labelled diagram to show the apparatus that is used to carry out this electrolysis in the laboratory.
(2)
ii)
Before the electrolysis, the masses of the electrodes were determined.
After the electrolysis, the electrodes were washed and dried and their masses re-determined.

Figure 6 shows these masses and the resulting changes in masses of the electrodes.

  mass of electrode
before electrolysis
in g
mass of electrode
after electrolysis
in g
change in mass
of electrode
in g
anode 11.27 10.42 − 0.85
cathode 11.32 12.17 + 0.85

Figure 6

Explain these results.

(4)

2c2 marks

Higher Only

When sodium sulfate solution is electrolysed, using inert electrodes, hydrogen is formed at the cathode.

Write the half equation for the formation of hydrogen gas, H2, from hydrogen ions, H+.

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3a3 marks

Copper(II) chloride and lead chloride are both ionic compounds.

i)
Explain why adding water to copper chloride will form an electrolyte.

[2]

ii)
State why adding water to lead chloride will not form an electrolyte.

[1]

3b2 marks

Describe what you would have to do to lead chloride so it acts as an electrolyte.

Give a reason for your answer.

3c2 marks

Higher Only

Copper(II) chloride solution is electrolysed.

Write the half equation for the reaction that happens at the anode.

3d2 marks

Higher Only

Explain why reduction happens at the cathode.

Use the movement of electrons in your answer.

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4a2 marks

Sodium chloride solution is electrolysed.
Hydrogen is formed at the cathode.

Describe the test you would use to prove that a gas is hydrogen.

4b2 marks

Explain how hydrogen is formed at the cathode.

4c3 marks

Universal indicator is added to the sodium chloride solution at the start.
Predict what colour the electrolyte will be at the end of the electrolysis reaction.

Give a reason for your answer.

4d1 mark

State the products formed when molten sodium chloride is electrolysed.

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5a1 mark

Figure 1 shows the apparatus used to metal plate an iron spoon.
The spoon is covered with a thin layer of silver.

edx-3-2h-q5a-electroplating-apparatus

Figure 1

Suggest a suitable solid compound that can be dissolved to make the electrolyte.

5b2 marks

Higher Only

Write the half equation to show what happens at the silver rod.

5c2 marks

Explain why the spoon needs to be connected to the negative side of the power supply.

5d1 mark

Suggest one way to increase the rate of electroplating.

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