Electrolysis explained: products at each electrode
See how electricity splits ionic compounds, and predict the products at the anode and cathode for molten and aqueous solutions.
GCSEA-LevelHigh SchoolCurriculum fit: GCSE Chemistry and Combined Science (electrolysis; separate Chemistry for more detail). US: high school physical science (chemical reactions and electrical energy).
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What is it?
Electrolysis uses an electric current to break down an ionic compound that is molten or dissolved in water. The ions are free to move, so they travel to the electrodes.
Positive ions (cations) move to the negative electrode (the cathode). Negative ions (anions) move to the positive electrode (the anode).
Key formulas and ideas
- Cathode (negative): positive ions gain electrons (reduction).
- Anode (positive): negative ions lose electrons (oxidation).
- In aqueous solutions, hydrogen forms at the cathode if the metal is more reactive than hydrogen.
- At the anode in aqueous solutions, a halogen forms if halide ions are present; otherwise oxygen forms.
Worked examples
Example 1: Molten compound
Question: Name the products when molten sodium chloride is electrolysed.
- Sodium ions (Na⁺) move to the cathode and become sodium metal.
- Chloride ions (Cl⁻) move to the anode and become chlorine gas.
Answer: Sodium at the cathode, chlorine at the anode
Example 2: Aqueous solution
Question: Name the products when copper sulfate solution is electrolysed with inert electrodes.
- Copper is less reactive than hydrogen, so copper forms at the cathode.
- Sulfate ions are not discharged, so oxygen forms at the anode from water.
Answer: Copper at the cathode, oxygen at the anode
Example 3: Why must the compound be molten or dissolved?
Question: Explain why solid sodium chloride does not conduct electricity.
- In a solid the ions are held in fixed positions.
- They cannot move to carry charge.
Answer: The ions are not free to move in a solid
Common mistakes
- Mixing up the cathode and anode charges.
- Forgetting that solids do not conduct because ions are fixed.
- Writing hydrogen at the cathode for every aqueous solution without checking reactivity.
- Using 'gain' and 'lose' electrons the wrong way round for reduction and oxidation.
Practice questions
Frequently asked questions
What is an inert electrode?
One that does not react, such as graphite or platinum.
What is electrolysis of brine used for?
Making chlorine, hydrogen and sodium hydroxide, which are important industrial chemicals.
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GCSEA-LevelHigh SchoolAPThe reactivity series: displacement reactions and extraction
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GCSEHigh SchoolSources and review
Reviewed by StudyMorrow editorial review on 5 Nov 2026.