Electrolyte – IGCSE Chemistry Definition
IGCSE Chemistry definition of electrolyte: an ionic compound that conducts electricity when molten or dissolved, decomposing in the process.
Published by IGCSEChemistry.com.my
Chemistry teaching team: K. S. Tan (15+ years teaching IGCSE Chemistry) and Ms Yash (10+ years teaching IGCSE Chemistry) and Ms Kartini (15+ years teaching IGCSE Chemistry).
Mapped to Cambridge IGCSE Chemistry 0620 (2026–2028). Last updated 2026-08-19.
An electrolyte is the substance that is decomposed during electrolysis. The 0620 syllabus requires you to define electrolyte, explain why it must be ionic, and understand why it must be molten or dissolved to conduct. This concept links bonding, structure, and electrochemistry.
The 0620 definition
An electrolyte is an ionic compound that conducts electricity when molten or dissolved in water, and is decomposed (broken down) by the passage of the current.
Why must it be ionic?
Electrolytes must contain ions because the current through the liquid is carried by the movement of ions, not electrons:
- Cations (positive ions) carry charge toward the cathode
- Anions (negative ions) carry charge toward the anode
Covalent compounds (such as sugar, ethanol, or distilled water) do not form ions when dissolved, so they cannot act as electrolytes.
Why must it be molten or dissolved?
| State | Ions | Conducts? | Is it an electrolyte? |
|---|---|---|---|
| Solid ionic compound | Fixed in lattice, cannot move | No | No (until melted or dissolved) |
| Molten ionic compound | Free to move | Yes | Yes |
| Dissolved ionic compound | Free to move in solution | Yes | Yes |
| Covalent compound (any state) | No ions present | No | No |
Common electrolytes in the 0620 syllabus
| Electrolyte | Type | Ions present |
|---|---|---|
| Molten lead(II) bromide | Molten | Pb²⁺, Br⁻ |
| Molten sodium chloride | Molten | Na⁺, Cl⁻ |
| Dilute sulfuric acid | Aqueous | H⁺, SO₄²⁻ (plus H⁺ and OH⁻ from water) |
| Copper(II) sulfate solution | Aqueous | Cu²⁺, SO₄²⁻ (plus H⁺ and OH⁻ from water) |
| Brine (conc. NaCl solution) | Aqueous | Na⁺, Cl⁻ (plus H⁺ and OH⁻ from water) |
Worked exam question
Explain why solid sodium chloride does not conduct electricity but molten sodium chloride does. (3)
Mark scheme
Sodium chloride is an ionic compound containing Na⁺ and Cl⁻ ions [1]; in the solid, ions are held in fixed positions in the lattice and cannot move [1]; when molten, the ions are free to move and carry the electric current [1]
Common exam mistakes
- Saying “electrolytes have free electrons”. Electrolytes conduct by the movement of ions, not electrons. Metals conduct by electron flow — that is a different mechanism.
- Calling water an electrolyte. Pure water contains very few ions and is an extremely poor conductor. It is not an electrolyte. However, water with dissolved ions (e.g. dilute sulfuric acid) is an electrolyte.
- Confusing electrode and electrolyte. The electrode is the solid conductor (graphite or metal). The electrolyte is the liquid ionic compound being decomposed.
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