A solution is a homogeneous mixture of two or more substances whose concentration may be altered with in certain limits. The substances which make up the solution are generally called its component. The solutions of two components are called binary solution. Similarly, the solutions of three and four components are called ternary and quaternary solution respectively. The components of a binary solution are called a solute and solvent. In general, a component which is present in excess is called the solvent while the component which is present in lesser quantity is termed the solute. Depending upon the physical states of the solute and the solvent, the solutions can be classified into the following nine types.
NB: Solid in liquid, liquid in liquid and gas in liquid are common solutions.
Solid in Liquid Solutions:
The point at which a liquid cannot dissolve more of the solute at a constant temperature is called saturated point and such solution is called saturated solution. A solution in which more of solute can be dissolved at a given temperature is called unsaturated solution. A solution may sometimes contain more solute than would be necessary to saturated it at a given temperature. Such solution is called super saturated solution.
The extent to which a solute is soluble in a solvent is expressed in terms of solubility. Therefore, “Solubility of a substance may be defined as the amount of solute dissolved in 100 gram of a solvent to form a saturated solution at a given temperature”.
Solubility = (Weight of solute/Weight of solvent) x 100
Solubility of a solid in liquid depends upon-
1) Nature of solute: Polar solvent can dissolve polar solute and non-polar solutes dissolve in non-polar solvents. e.g. ionic substance such as NaCI, KCI, KNO3 etc. have larger solubility in polar solvent like water but they have poor solubility in non-polar solvent like CCl4, CS2, etc.
2) Temperature: Solubility of a solid in liquid increases with raise in temperature and decreases with decrease in temperature.