Solubilitet

Solubilitet refers to the ability of a substance, the solute, to dissolve in a solvent to form a homogeneous solution at a given temperature and pressure. The amount that can dissolve is called the solubility, and it is commonly expressed in units such as grams of solute per 100 milliliters of solvent, molarity, or mole fraction. Solubility depends on the chemical nature of the solute and solvent and on conditions such as temperature and pressure.

The concept covers several cases. Substances dissolved in liquids, such as solids in water (for example, salt or sugar), are described by solubility curves. Liquids can be miscible with each other, forming a single phase. Gases dissolved in liquids are governed by different principles; their solubility generally increases with pressure and often decreases with rising temperature, a relationship described by Henry’s law for many systems.

Solubility is not the same as the rate at which a substance dissolves. A substance may dissolve quickly but have a low equilibrium solubility, or dissolve slowly yet reach a high saturated amount given enough time.

In sparingly soluble salts, the solubility is related to the solubility product, Ksp. The dissolution is an equilibrium, and at saturation the product of the concentrations of the constituent ions equals Ksp. Apparent solubility can be affected by the common ion effect, complexation, and pH.

Applications of solubility knowledge include pharmaceutical formulation, environmental science, and food chemistry. Examples: sodium chloride is highly soluble in water; calcium sulfate has low solubility; carbon dioxide is more soluble under higher pressure; sugar is highly soluble in water. Solubility data and curves support prediction and design in various processes.