Solubility

The solubility of a substance is the maximum quantity of it that can be dissolved in a fixed amount of a particular solvent at a stated temperature (and, for gases, a stated pressure). Once this limit is reached, no further solute will go into solution under those conditions — the solution is then said to be saturated. A solution that can still take up more solute is unsaturated.

Solubility is not a single fixed number for a substance; it is governed by several factors working together:

• the nature of the solute and the solvent — how similar their chemical character and intermolecular forces are,
• the temperature at which dissolution takes place, and
• the pressure (this matters chiefly for gases, and hardly at all for solids and liquids).

Because a solute may be a solid or a gas dissolving in a liquid, and each behaves differently towards temperature and pressure, it is useful to treat the two cases separately. The sections that follow look first at how a solid dissolves in a liquid, and then at how a gas dissolves in a liquid. …