Electrolysis is the decomposition of an electrolyte (a molten or dissolved ionic compound) by passing an electric current through it. The substance that conducts electricity and is decomposed is called the electrolyte.
Key Terms
- Anode: the positive electrode — attracts anions (negative ions).
- Cathode: the negative electrode — attracts cations (positive ions).
- Anions are oxidised (lose electrons) at the anode; cations are reduced (gain electrons) at the cathode.
Electrolysis of Sodium Chloride (brine)
- At the cathode: hydrogen gas is produced (H⁺ ions gain electrons).
- At the anode: chlorine gas is produced (Cl⁻ ions lose electrons).
- In solution, sodium hydroxide remains in the cell.
Electrolysis of Copper(II) Sulphate
- With copper electrodes: copper is deposited at the cathode (purification).
- With inert (carbon) electrodes: copper deposits at the cathode and oxygen is released at the anode.
Uses of Electrolysis
- Extraction of reactive metals (e.g. aluminium from its ore).
- Purification (refining) of metals such as copper.
- Electroplating (coating objects with a metal).
Remember the products: Cations go to the cathode and gain electrons; anions go to the anode and lose electrons. Positive attracts negative.
Summary
Electrolysis uses a direct current to decompose an electrolyte into its elements. Metal (or hydrogen) forms at the cathode and non-metal (e.g. chlorine or oxygen) at the anode. It is used in metal extraction, refining and electroplating.
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