The Process of Electrolysis
Build confidence in The Process of Electrolysis for GCSE Chemistry with this free worksheet and full mark scheme — Foundation and Higher exam-style questions with worked answers for AQA, Edexcel and OCR. Electrolysis uses electricity to break down an ionic compound; positive ions move to the cathode and negative ions to the anode.
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These worksheets and mark schemes are original, written for Virtus Academy and checked against the current AQA, Edexcel and OCR specifications. Every worksheet comes with a full mark scheme.
Topic overview
Electrolysis is the breaking down of an ionic compound using electricity. The compound must be molten or dissolved so the ions are free to move.
The liquid or solution containing the ions is called the electrolyte. Two electrodes are placed in it: the cathode is negative and the anode is positive. Positive ions move to the negative cathode, and negative ions move to the positive anode.
At the electrodes the ions gain or lose electrons and become neutral atoms or molecules, which are then discharged. Positive ions gain electrons at the cathode, which is reduction; negative ions lose electrons at the anode, which is oxidation.
Revision notes
The setup
The electrolyte is the molten or dissolved ionic compound containing free-moving ions.
The cathode is the negative electrode and the anode is the positive electrode. Electrodes are usually inert, made of graphite or platinum, so they do not react.
Movement of ions
Positive ions, called cations, move to the negative cathode.
Negative ions, called anions, move to the positive anode. Opposite charges attract, which is what drives the movement.
What happens at the electrodes
At the cathode, positive ions gain electrons — this is reduction.
At the anode, negative ions lose electrons — this is oxidation. The ions become neutral atoms or molecules and are discharged as products.
Key points
- Electrolysis breaks down ionic compounds using electricity.
- The compound must be molten or dissolved.
- The electrolyte contains free-moving ions.
- The cathode is negative; the anode is positive.
- Positive ions move to the cathode and are reduced.
- Negative ions move to the anode and are oxidised.
Worked examples
Example 1
Explain why an ionic compound must be molten or dissolved for electrolysis. [2 marks]
Model answer
In a solid the ions are held in fixed positions in the lattice and cannot move (1 mark). Melting or dissolving frees the ions so they can move to the electrodes and carry charge (1 mark).
Example 2
State which electrode positive ions move to and what happens to them there. [2 marks]
Model answer
They move to the cathode, the negative electrode (1 mark), where they gain electrons and are reduced (1 mark).
Example 3
Explain why the electrodes are usually made of graphite or platinum. [2 marks]
Model answer
These materials are inert (1 mark), so they do not react with the electrolyte or the products formed (1 mark).
Common mistakes
Confusing cathode and anode.
The cathode is negative and attracts positive ions; the anode is positive.
Saying solid ionic compounds can be electrolysed.
The ions must be free to move, so the compound must be molten or dissolved.
Getting oxidation and reduction the wrong way round.
Cathode: gain electrons, reduction. Anode: lose electrons, oxidation.
Saying electrons move through the electrolyte.
Ions carry the charge through the electrolyte; electrons flow through the wires.
Exam tips
- Remember the cathode is negative and attracts positive ions.
- Link reduction to the cathode and oxidation to the anode.
- Explain why the compound must be molten or dissolved.
- Say ions carry charge through the electrolyte.
Key terms
- Electrolysis
- Breaking down an ionic compound using electricity.
- Electrolyte
- The molten or dissolved compound containing free ions.
- Cathode
- The negative electrode, where reduction occurs.
- Anode
- The positive electrode, where oxidation occurs.
Related topics
Written and reviewed against the current AQA, Edexcel and OCR specifications. Spotted an error? Let us know.