watersolubility

Water solubility, sometimes written as watersolubility, is the extent to which a substance can dissolve in water to form a homogeneous solution. It arises from the balance between interactions of the solute with water (hydrogen bonding, dipole-dipole interactions, and ion-dipole interactions) and the forces holding the solute together. Generally, polar and ionic substances are more water-soluble, while nonpolar compounds tend to be poorly soluble. The principle of “like dissolves like” summarizes this tendency.

Solubility is influenced by several factors. Temperature often increases the solubility of most solid solutes in water, whereas gas solubility in water typically decreases with temperature. Pressure predominantly affects the solubility of gases: higher pressure increases gas solubility in water (described by Henry’s law). For ionic compounds, solubility depends on lattice energy and hydration energy, and can be affected by pH, ionization, and the presence of other ions (common ion effect). The pH can change the charge state of acidic or basic solutes, altering their solubility.

Solubility is commonly expressed as the maximum amount of solute that can dissolve at a given temperature to form a saturated solution, with units such as grams per 100 grams of water or moles per liter. For sparingly soluble salts, the solubility product constant (Ksp) characterizes the equilibrium between solid and dissolved ions.

Applications of water solubility include drug formulation and bioavailability, environmental fate of contaminants, and various industrial and food processes. Related considerations include dissolution rate (kinetics) and methods to enhance apparent solubility, such as using co-solvents or surfactants.