These liquids and solutions are able to conduct electricity and are called…

The idea

A liquid or solution that contains mobile ions can conduct electricity and is called an electrolyte. The mobile ions carry charge through the electrolyte, so a current flows. For example, molten lead bromide and copper sulfate solution are electrolytes because they contain mobile ions. In contrast, pure water and solid ionic compounds are not electrolytes in this sense because they do not contain mobile ions. The term electrolyte therefore describes the substance being electrolysed, not the electrodes or the wires. Recognising an electrolyte means checking that ions are free to move within the liquid or solution.

What earns the marks

• An electrolyte is a liquid or solution that contains mobile ions and can conduct electricity.
• Conduction occurs because mobile ions carry charge through the electrolyte.
• Molten ionic compounds and aqueous solutions of ionic compounds are examples of electrolytes.
• Pure water and solid ionic compounds are not electrolytes because they lack mobile ions.
• The term electrolyte refers to the substance being electrolysed, not to the electrodes or external circuit.

Common mistakes and how to put them right

• Calling any liquid an electrolyte.

  Put it right: An electrolyte must contain mobile ions.

• Confusing the electrolyte with the electrodes.

  Put it right: The electrolyte is the liquid or solution being electrolysed.

• Thinking that all solutions conduct equally.

  Put it right: Conduction depends on the presence and mobility of ions.

Exam tips

• Define an electrolyte in terms of mobile ions and electrical conduction.
• Give a named example and state the mobile ions present to support the definition.
• Contrast an electrolyte with a non-electrolyte such as pure water to show understanding.