Aqueous Solution Definition in Chemistry

An aqueous solution is any solution in which water (H₂O) is the solvent. In a chemical equation, the symbol (aq) follows a species name to indicate that it is in aqueous solution. For example, dissolving salt in water has the chemical reaction:

NaCl(s) → Na⁺(aq) + Cl^-(aq)

Although water is often called the universal solvent, it dissolves only substances that are hydrophilic in nature. Examples of hydrophilic molecules include acids, bases, and many salts. Substances that are hydrophobic do not dissolve well in water and tend not to form aqueous solutions. Examples include many organic molecules, including fats and oils.

When electrolytes—such as NaCl and KCl—dissolve in water, the ions allow the solution to conduct electricity. Nonelectrolytes like sugar also dissolve in water, but the molecule remains intact and the solution is not conductive.

Aqueous Solution Examples

Cola, saltwater, rain, acid solutions, base solutions, and salt solutions are examples of aqueous solutions. 

Examples of solutions that are not aqueous solutions include any liquid that does not contain water. Vegetable oil, toluene, acetone, carbon tetrachloride, and solutions made using these solvents are not aqueous solutions. Similarly, if a mixture contains water but no solute dissolves in the water as a solvent, an aqueous solution is not formed. For example, mixing sand and water does not produce an aqueous solution.