Chemistry · Unit 9

Electrolysis

Splitting compounds with electricity

Electrolysis uses electricity to force reactions that would not happen on their own, which makes it the industrial method for extracting the most reactive metals.

The unit covers the basic set-up, what happens at each electrode, predicting the products from the ions present, electroplating, and the industrial applications.

This unit breaks down into 20 short steps and 120 questions, starting at difficulty 1 and building to 3. Below you can see exactly what it covers, how the path is structured, and worked examples with explanations.

Steps: 20
Questions: 120
Difficulty: 1-3

What this unit covers

Electrolysis Basics
Electrodes and Ions
Predicting Products
Electroplating
Industrial Uses

Where this fits

Needs Redox Reactions. Connects to Metals and Extraction.

Where people slip

The anode is positive in electrolysis and negative in a cell, which is exactly backwards from what most people remember. Work from where oxidation happens instead - it is always the anode.

How the unit is structured

Electrolysis runs as 20 short steps that unlock in order. 15 are practice rounds and 5 are challenge rounds that pull together everything before them. Questions start at difficulty 1 and climb to 3 as you progress.

Step 1 · easierStep 20 · harder

Challenge rounds

Example questions

30 real questions from this unit, with the answer and the reason behind it, grouped by what they practise. There are 120 in the unit altogether.

Electrodes and Ions

Fill the blankLevel 1
1. The negative electrode in an electrolysis cell is called the ____.
- cathodecorrect
- anode
- anion
- electrolyte
The negative electrode is the cathode, which attracts positive ions.
Multiple choiceLevel 1
2. In electrolysis, what is the positive electrode called?
- The anodecorrect
- The cathode
- The electrolyte
- The cation
The positive electrode is the anode.
Fact or fibLevel 2
3. Negative ions, called anions, move towards the anode during electrolysis.
Answer: True
Anions are negative and are attracted to the positive anode, so the statement is true.
Match the pairsLevel 2
4. Match each electrolysis term to its meaning.
Answer: Anode = Positive electrode; Cathode = Negative electrode; Cation = Positive ion; Anion = Negative ion
The anode is positive, the cathode is negative, cations are positive ions and anions are negative ions.
Odd one outLevel 2
5. Three of these are unreactive (inert) electrode materials. Which is the odd one out?
- Coppercorrect
- Platinum
- Graphite
- Gold
Copper is an active electrode that dissolves and takes part in the reaction, unlike inert platinum, graphite and gold.
Guess the numberLevel 3
6. How many moles of electrons are needed to deposit 1 mole of aluminium from Al3+ ions? (Al3+ + 3e- -> Al)
Answer: 3 moles
Each Al3+ ion gains 3 electrons, so 3 moles of electrons deposit 1 mole of aluminium.

Electrolysis Basics

Fill the blankLevel 1
7. The molten or dissolved substance that is broken down during electrolysis is called the ____.
- electrolytecorrect
- electrode
- insulator
- catalyst
The electrolyte is the ionic liquid or solution that conducts the current and is decomposed.
Guess the numberLevel 1
8. How many electrodes must be dipped into the electrolyte to build a simple electrolysis circuit?
Answer: 2 electrodes
Two electrodes, an anode and a cathode, are needed so current can flow through the electrolyte.
Multiple choiceLevel 1
9. What happens during electrolysis?
- A compound is broken down using an electric currentcorrect
- Two elements join to make a compound
- A metal rusts slowly in air
- A liquid simply boils into a gas
Electrolysis uses an electric current to break down a compound into simpler substances.
Picture questionLevel 1
10. 🔋 A battery like this powers an electrolysis cell. What does electrolysis need a supply of to work?
- Direct current (electricity)correct
- Bright sunlight only
- Loud sound waves
- Cold air
Electrolysis needs a supply of direct current electrical energy to push the reaction along.
Build the sentenceLevel 2
11. Build the sentence that defines electrolysis.
Answer: electrolysis splits a compound using electricity
Electrolysis splits a compound using electricity.
Fact or fibLevel 2
12. Electrolysis needs an external electrical power supply to drive the reaction.
Answer: True
Electrolysis is a non-spontaneous decomposition, so an external power supply must provide the energy.

Electroplating

Multiple choiceLevel 1
13. What is electroplating?
- Coating an object with a thin layer of metal using electrolysiscorrect
- Melting a metal to reshape it
- Mixing two metals to make an alloy
- Scraping rust off with sandpaper
Electroplating uses electrolysis to coat an object with a thin layer of metal.
Choose all that applyLevel 2
14. Which of these are genuine reasons to electroplate an object? Select all that apply.
- To protect it from corrosioncorrect
- To make it look more attractivecorrect
- To use only a thin layer of an expensive metalcorrect
- To make it radioactive
Electroplating protects against corrosion, improves appearance and can save money by using only a thin layer of an expensive metal.
Fill the blankLevel 2
15. During electroplating, the object being coated is connected as the ____.
- cathodecorrect
- anode
- electrolyte
- switch
The object to be plated is made the cathode so metal ions are deposited onto it.
Picture questionLevel 2
16. 🥫 This steel food can has been coated with a thin layer of tin using electrolysis to stop it rusting. What is this coating process an example of?
- Electroplatingcorrect
- Anodising
- Electrowinning
- Smelting
Coating one metal with a thin layer of another using electrolysis is called electroplating.
Fact or fibLevel 3
17. When a metal anode is used, the mass it loses is about equal to the mass gained by the cathode.
Answer: True
As the anode dissolves it replaces the ions deposited on the cathode, so it loses roughly the same mass the cathode gains.
Guess the numberLevel 3
18. A current of 9.65 A flows for 1000 s through silver nitrate solution. What mass of silver is deposited? (Ag+ + e- -> Ag, Ar Ag = 108, F = 96500 C/mol)
Answer: 10.8 g
Q = It = 9650 C gives 0.1 mol electrons; since Ag+ + e- -> Ag, 0.1 mol (10.8 g) of silver is deposited.

Industrial Uses

Multiple choiceLevel 1
19. Aluminium is extracted by electrolysis from which ore?
- Bauxitecorrect
- Haematite
- Limestone
- Malachite
Aluminium is obtained from bauxite, an ore rich in aluminium oxide.
Build the sentenceLevel 2
20. Build the sentence explaining why extracting aluminium by electrolysis is expensive.
Answer: electrolysis uses large amounts of electrical energy
Aluminium extraction is costly mainly because electrolysis uses large amounts of electrical energy to keep the ore molten and drive the reaction.
Fill the blankLevel 2
21. Metals more reactive than carbon are extracted from their molten ores using ____.
- electrolysiscorrect
- filtration
- distillation
- evaporation
Reactive metals such as sodium and aluminium are too reactive for carbon reduction, so electrolysis is used.
Guess the numberLevel 2
22. Roughly what temperature, in degrees C, does the Hall-Heroult cell operate at once aluminium oxide is dissolved in molten cryolite?
Answer: 950 degrees C
Dissolving alumina in cryolite lets the cell run at about 950 C, far below alumina's melting point of over 2000 C.
Choose all that applyLevel 3
23. Which statements about the electrowinning of copper are correct? Select all that apply.
- Copper metal is deposited from a solution containing copper ionscorrect
- An inert anode that does not dissolve is usedcorrect
- Oxygen gas is released at the anodecorrect
- The anode is a block of impure copper that dissolves
- Sodium metal is produced at the cathode
In electrowinning, copper is deposited from a solution of its ions using an inert anode, at which oxygen is released.
Match the pairsLevel 3
24. Match each product of the chlor-alkali (brine) process to a use or role.
Answer: Chlorine = Making bleach; Hydrogen = Making ammonia; Sodium hydroxide = Making soap; Sodium chloride = The starting electrolyte
Chlorine makes bleach, hydrogen helps make ammonia, sodium hydroxide makes soap, and sodium chloride is the starting electrolyte.

Predicting Products

Multiple choiceLevel 1
25. Electrolysis of water produces which two gases?
- Hydrogen and oxygencorrect
- Carbon dioxide and water vapour
- Nitrogen and hydrogen
- Chlorine and oxygen
Water splits into hydrogen gas and oxygen gas during electrolysis.
Fact or fibLevel 2
26. In the Downs process for extracting sodium, chlorine gas is produced at the anode as a useful by-product.
Answer: True
Chloride ions are oxidised at the anode, so the Downs cell yields chlorine gas alongside the sodium metal.
Fill the blankLevel 2
27. In the electrolysis of water, oxygen gas bubbles off at the ____.
- anodecorrect
- cathode
- electrolyte
- battery
Oxygen forms at the positive anode during the electrolysis of water.
Guess the numberLevel 2
28. In the electrolysis of water, how many volumes of hydrogen are made for every 1 volume of oxygen?
Answer: 2 volumes
Water is H2O, so twice as much hydrogen is produced, giving a 2:1 hydrogen to oxygen ratio.
Picture questionLevel 2
29. 🔋 Molten lead bromide (PbBr2) is electrolysed. Which product forms at the negative cathode?
- Leadcorrect
- Bromine
- Hydrogen
- Oxygen
In molten lead bromide the lead ions are reduced at the cathode (Pb2+ + 2e- -> Pb), while bromine forms at the anode.
Choose all that applyLevel 3
30. Which substances are made when concentrated sodium chloride solution (brine) is electrolysed? Select all that apply.
- Hydrogencorrect
- Chlorinecorrect
- Sodium hydroxidecorrect
- Sodium metal
Electrolysis of brine gives hydrogen at the cathode, chlorine at the anode and sodium hydroxide left in solution.

Where these questions come from. Each unit starts as a plan of the concepts it should cover and the difficulty it should span. Questions are written against that plan with AI assistance, then checked by a validator that rejects anything without a single defensible answer, an explanation, or plausible wrong options. How we write questions sets out the whole process, and corrections are fixed in the bank and reach the site and the app the same day.

How you practise

This unit mixes 17 different question formats, so you are recalling and applying rather than recognising the same layout every time.

Build the sentence
Choose all that apply
Fact or fib
Fill the blank
Guess the number
Listen and choose
Match the pairs
Multiple choice
Odd one out
Picture question
Put in order
Sequence recall
Sort into groups
Spell it
Tap the pairs
True or false
Type the answer

Practise Electrolysis

120 questions across 20 steps. Start with step one and crawl at your own pace.

Play this unit

Read about Electrolysis

Explainers from our blog on what this unit covers. Each one ends with real questions from the bank.

What Is Electrolysis? Using Electricity to Drive Chemical ChangeLearn how electric current drives non-spontaneous chemical reactions, what happens at electrodes, and how ions move in an electrolyte.August 14, 2026 · 6 min read

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