An electrolyte is a substance that conducts electricity when molten or in aqueous solution and is decomposed by it, because it contains freely moving ions.
An electrolyte is a substance that conducts electricity when molten or in aqueous solution and is decomposed by it, because it contains freely moving ions. Malay: elektrolit · Chinese: 电解质.
The key idea is the freely moving ions. In a solid ionic compound the ions are locked in a lattice and cannot move, so it does not conduct; once the compound is melted or dissolved, the ions are free to carry charge to the electrodes, where they are discharged. Ionic compounds, acids and alkalis are electrolytes. Substances that conduct without being decomposed, such as metals and graphite, are not electrolytes but conductors, and molecular substances such as sugar solution do not conduct at all because they have no ions.
Example. Molten sodium chloride is an electrolyte: when melted, its Na+ and Cl− ions move freely, so it conducts and is decomposed into sodium and chlorine. Solid sodium chloride, by contrast, does not conduct, because its ions are held rigidly in the lattice.
Confusion to avoid. Do not call every conductor an electrolyte. Copper wire conducts but is not decomposed, so it is a conductor, not an electrolyte. Also be careful with strong and weak electrolytes: a weak electrolyte such as ethanoic acid only partly ionises, so it conducts poorly, while a strong electrolyte ionises fully and conducts well.
Testing for an electrolyte. A simple way to identify an electrolyte in the laboratory is to complete a circuit with a bulb or ammeter through the substance. An electrolyte lights the bulb only when it is molten or dissolved, never as a dry solid, and bubbles of gas or a fresh deposit at the electrodes show that it is being decomposed rather than merely carrying a current. This test also separates strong electrolytes, which light the bulb brightly, from weak ones, which light it dimly.
The electrolyte is where all the action of electrolysis takes place, so understanding it correctly is the starting point for electrodes, selective discharge and cells throughout this chapter, and its definition is a common one-mark item in SPM Chemistry.
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