solubility

Solubility is the property of a substance (the solute) to dissolve in a solvent to form a homogeneous solution at a given temperature and pressure. It is defined as the maximum amount of solute that can dissolve to yield a saturated solution, beyond which undissolved solid remains. Solubility is influenced by interactions between solute and solvent, including polarity, hydrogen bonding, and lattice energy of the solid.

Solubility is often expressed as grams of solute per 100 grams of solvent, or as molarity (moles per liter) or molar solubility (moles per liter) that dissolve at the temperature. For gases in liquids, Henry's law applies: the concentration of a dissolved gas is proportional to its partial pressure above the solution.

Temperature and pressure affect solubility. For most solid solutes in liquids, solubility increases with temperature. For gases, solubility decreases with rising temperature and increases with increasing pressure. Some solutes show more complex behavior.

Solubility depends on solvent-solute compatibility. Polar solvents dissolve polar or ionic solutes; nonpolar solvents dissolve nonpolar solutes. The lattice enthalpy of a crystalline solid and the hydration enthalpy determine the dissolution driving force. The common ion effect can reduce solubility when ions common to a soluble salt are present, shifting the dissolution equilibrium.

Sparingly soluble salts are described by a solubility product constant, Ksp, reflecting the equilibrium between solid and dissolved ions. Examples: NaCl is highly soluble in water; AgCl has low solubility; CO2 dissolves in water forming carbonic acid.