In chemistry, a homogeneous mixture is defined as a solution in which one or more substances are contained in a liquid or solid or gaseous phase; it contains different particles mixed and distributed evenly in the space available so that each volume of the solution has the same composition as the others. It is used to call solute (or dispersed phase) the substance (or substances) in smaller quantities, and solvent (or dispersed phase or continuous phase) the substance in greater quantities.
A solution differs from a generic dispersion because the solute is dispersed in the solvent at the level of individual molecules or ions, each of them surrounded by solvent molecules (we speak more precisely of solvation). When, in a solution, a solute is present with atoms, ions, or molecules of particularly small dimensions (less than 1 nm), invisible even with the aid of the microscope, we speak of a true solution. Otherwise, when the particle size of the solute is between 1 and 1000 nm, we speak of colloidal dispersion.
Solubility is the property of a solid, liquid, or a gaseous chemical substance called solute to dissolve in a solid, liquid, or gaseous solvent. It is usually expressed in grams per 100 g of solvent at a specified temperature.
According to the IUPAC definition, solubility is the analytical composition of a saturated solution expressed as a proportion of a designated solute in a designated solvent. Solubility may be stated in various units of concentration such as molarity, molality, mole fraction, mole ratio, mass (solute) per volume (solvent), and other units.
The system of analysis used for identifying the metallic ions present in a mixture of inorganic compounds depends upon the very low solubilities of certain salts of the metals.