solute

A solute is the substance dissolved in a solvent to form a solution. In a homogeneous mixture, the solute is present in a smaller amount than the solvent, and it disperses at the molecular level throughout the solvent.

Solubility describes how much solute can dissolve in a given amount of solvent at a specific temperature and pressure. The solvent is the component in the larger amount and determines the phase of the solution; however, which substance is called solvent can depend on the context.

Common solutes include table salt (sodium chloride) in water, and sugar in water. Solutes can be electrolytes, which dissociate into ions in solution, or non-electrolytes, which do not. Gases such as oxygen or carbon dioxide can also be solutes in liquids.

Concentrations are used to quantify solutes, including molarity, molality, mass percent, and mole fraction. A solution that contains the maximum amount of solute at a given temperature is saturated; one that can still absorb more solute is unsaturated; if the solution contains more solute than it can hold, it is supersaturated.

Factors influencing dissolution include temperature, pressure (for gases), particle size, surface area, stirring, and the nature of the solute and solvent. Dissolution is often described by rate and extent, and the resulting interactions are described by concepts such as solvation and hydration.

Solutes affect properties of solutions, including boiling and freezing points, vapor pressure, and osmotic behavior, collectively known as colligative properties when the effects depend only on solute particle number.