Editing Ideal solution (section)

== Non-ideality ==

Deviations from ideality can be described by the use of [[Margules function]]s or [[activity coefficient]]s.  A single Margules parameter may be sufficient to describe the properties of the solution if the deviations from ideality  are modest; such solutions are termed ''[[regular solution|regular]]''.

In contrast to ideal solutions, where volumes are strictly additive and mixing is always complete, the volume of a non-ideal solution is not, in general, the simple sum of the volumes of the component pure liquids and [[solubility]] is not guaranteed over the whole composition range. By measurement of densities, [[thermodynamic activity]] of components can be determined.