Aqueous solution

thumb|right|The first [[solvation shell of a sodium ion dissolved in water]]

An aqueous solution is a solution in which the solvent is water. It is mostly shown in chemical equations by appending (aq) to the relevant chemical formula. For example, a solution of table salt, also known as sodium chloride (NaCl), in water would be represented as . The word aqueous (which comes from aqua) means pertaining to, related to, similar to, or dissolved in, water. As water is an excellent solvent and is also naturally abundant, it is a ubiquitous solvent in chemistry. Since water is frequently used as the solvent in experiments, the word solution refers to an aqueous solution, unless the solvent is specified.

A non-aqueous solution is a solution in which the solvent is a liquid, but is not water.

Characteristics

Substances that are hydrophobic ('water-fearing') do not dissolve well in water, whereas those that are hydrophilic ('water-loving') do. An example of a hydrophilic substance is sodium chloride. In an aqueous solution the hydrogen ions () and hydroxide ions () are in Arrhenius balance ([] [] = K_w = 1 × 10⁻¹⁴ at 298 K).

Acids and bases are aqueous solutions, as part of their Arrhenius definitions.