The process of electrolysis — AQA GCSE Chemistry
Test yourself on The process of electrolysis with AQA GCSE practice questions.
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The process of electrolysis explained
During electrolysis, ions in an electrolyte move to the electrode of opposite charge.
Read the full explanation
Positive ions (cations) are attracted to the negative cathode, where they gain electrons and are discharged as neutral atoms. Negative ions (anions) are attracted to the positive anode, where they lose electrons and are discharged as neutral atoms. For example, in molten lead bromide, Pb²⁺ ions gain electrons at the cathode to form lead metal, while Br⁻ ions lose electrons at the anode to form bromine molecules. The discharge of ions produces elements because the neutral atoms formed are the elements themselves. This process requires a direct current supply. Inert electrodes are often used so they do not react, but reactive electrodes are sometimes used, such as carbon anodes in aluminium extraction.
Your focus
- Identify the electrode at which each type of ion is discharged.
- Explain how the gain or loss of electrons leads to the formation of elements.
- Apply the concept of discharge to predict the products of electrolysis of a given binary ionic compound.
The process of electrolysis exam tips
Marking Points
- Cations (positive ions) move to the cathode (negative electrode) and gain electrons to form neutral atoms.
- Anions (negative ions) move to the anode (positive electrode) and lose electrons to form neutral atoms.
- Discharge produces elements because the neutral atoms formed are the elements themselves.
- The electrolyte must contain mobile ions, either molten or in aqueous solution.
- Electrodes can be inert (like platinum) to prevent reaction, or reactive (like carbon in aluminium extraction) depending on the process.
Examiner Tips
- 💡When describing discharge, always state the electrode, the ion, and whether electrons are gained or lost.
- 💡Use the terms cation and anion correctly to show understanding of charge.
- 💡Link the discharge to the formation of a neutral element, naming the product.
Common Mistakes
- Confusing the polarity of electrodes: the cathode is negative and attracts positive ions; the anode is positive and attracts negative ions. Correction: remember 'cations go to cathode' and 'anions go to anode'.
- Thinking that ions gain or lose protons rather than electrons. Correction: discharge involves electron transfer, not proton transfer.
- Assuming that solid ionic compounds conduct electricity. Correction: the ions must be mobile, so the compound must be molten or dissolved in water.