Electrolyte and Nonelectrolyte Solutions

Water can dissolve many substances because of its chemical composition. Although its overall electrical charge is neutral, a water molecule has a partial negative charge at its oxygen end, and a partial positive charge at each of its hydrogen ends. This makes water a polar solvent.

When an ionic solute, such as a solid ionic compound, is added to water, the water molecules interact with the ions of the solute.

If the strong solute–solvent attractive forces overcome the solute–solute interactions holding the compound together, the solute ions are pulled apart.

The polar water molecules surround, or ‘hydrate’, the ions as they are separated. The hydrated ions are then dispersed uniformly throughout the solution.

When an electric potential is applied to an ionic solution, the ions become charge carriers that move towards the oppositely charged electrodes. This creates a current in the solution; in other words, it conducts electricity.

Substances that produce electrically conductive solutions when dissolved in polar solvents are called electrolytes. Sodium chloride is one such example.

However, when a molecular compound such as sucrose dissolves in water, its molecules remain intact as they become surrounded by water molecules. The solution contains only neutral sucrose molecules and therefore does not conduct electricity.

Substances that do not produce electrically conductive solutions when dissolved in polar solvents are called non-electrolytes.

How much of a compound dissociates into ions determines its strength as an electrolyte.

Nearly every molecule of a strong electrolyte, such as a strong acid like hydrochloric acid, will dissociate into ions in water, making the solution a good conductor of electricity.

On the other hand, only some molecules of a weak electrolyte, such as a weak acid like hydrofluoric acid, will dissociate into ions. Therefore, it can only conduct electricity to a small degree.