A solution is a mixture in which substances are intermixed so intimately that they can not be observed as separate components”. The dispersed phase or the substance which is to be dissolved is called solute, while the dispersion medium in which the solute is dispersed to get a homogenous mixture is called the solvent.

Solubility : “Solubility of a substance may be defined as the amount of solute dissolved in l00 gms of a solvent to form a saturated solution at a given temperature”.

A saturated solution is a solution which contains at a given temperature as much solute as it can hold in presence of dissolving solvent. Any solution may contain less solute than would be necessary to saturate it.

When the solution contains more solute than would be necessary to saturate it then it is termed as supersaturated solution.

Kinds of solutions : All the three states of matter (gas, liquid or solid) may behave either as solvent or solute. Depending on the state of solute or solvent, mainly there may be following nine types of binary solutions.

Among these solutions the most significant type of solutions are those which are in liquid phase and may be categorised as,

(1) Solid in liquid solutions,

(2) Liquid in liquid solutions and

(3) Gas in liquid solutions.