General Knowledge

Mixture and there Types


A material obtained by mixing two or more substances in any indefinite proportion is called a mixture. The properties of the components in a mixture remain unchanged.
Example— Milk, Sea water, Petrol, Paint, Glass, Cement, Wood etc.

There are two types of mixture
1. Homogeneous mixture
2. Heterogeneous mixture

1. Homogeneous mixture

A mixture is said to be homogeneous if it has a uniform composition throughout and there are no visible boundaries of separation between constituents. Moreover, the constituents cannot be seen even by a microscope.
Examples — Common salt dissolved in water, sugar dissolved in water, iodine dissolved in CC14, benzene in toluene and methyl alcohol in water.

2. Heterogeneous mixture

A mixture is said to be heterogeneous if it does not have a uniform composition throughout and has visible boundaries of separation between the various constituents. The different constituents of the heterogeneous mixture can be seen even with naked eye.
Example — A mixture of Sulphur & Sand, A mixture of Iron filings & Sand etc.

Colloidal Solution

These kinds of solutions are heterogeneous in nature and contain two phases, i.e., dispersed phase and dispersed medium. They can scatter light because of the presence of large solute particles, i.e., they show Tyndall effect and Brownian movement. (Blue colour of the sky is also due to scattering of light by dust particles suspended in air).
» Colloidal solutions are purified by dialysis.

Separation of mixture

1. Sublimation

In this process, a solid substance passes direct into its vapours on application of heat. The vapours when cooled, give back the original substance. This method can be used for the substances which are sublime in their separation from non-sublimate materials.
Examples of sublimes are Naphthalene, Iodine, Ammonium Chloride etc.

2. Filtration

This is a process for quick and complete removal of suspended solid particles from a liquid, by passing the suspension through a filter paper.
Examples—(i) removed of solid particles from the engine oil in car engine,
                    (ii) filtration of tea from tea leaves in the preparation of tea etc.

3. Evaporation

If a solution of solid substance in a liquid is heated, the liquid gets converted into its vapours and slowly goes off completely. This process is called evaporation.
Example—(i) Evaporation of water in summer from Ponds, wells & lakes,
                    (ii) Preparation of common salt from sea water by evaporation of water.

4. Crystallization

This method is mostly used for separation and purification of solid substances. In this process, the impure solid or mixture is heated with suitable solvent (e.g. alcohol, water, acetone, chloroform) to its boiling point and the hot solution is filtered. The clear filtrate is cooled slowly to room temperature, when pure solid ctystallizes out. This is separated by filtration and dried.
      For the separation of more complex mixtures, fractional crystallization is used, in which the components of the mixtures crystallize out at different interval of time.

5. Distillation

It is a process of converting a liquid into its vapour by heating and then condensing the vapour again into the same liquid by cooling. Thus, distillation involves vaporization and condensation both
      Distillation = Vaporization + Condensation
This method is employed to separate the liquids which have different boiling points or a liquid from non-volatile solid or solids either in solution or suspension. Example—A mixture of copper sulphate and water or a mixture of water (B.P 100°C) and methyl alcohol (B.P 45°C) can be separated by this method.

6. Fractional distillation

This process is similar to the distillation process except that a fractionating column is used to separate two or more volatile liquid which have different boiling points.
(i) Methyl alcohol (bp = 338 K) and acetone (bp = 329 K) can be separated by fractional distillation process,
(ii) Separation of petrol, diesel oil, kerosene oil, heavy oil etc from crude petroleum,
(iii) Separation of oxygen, nitrogen inert gasses and carbon dioxide from liquid air etc.

7. Chromatography

The name chromatography is derived from Latin word 'Chroma' meaning color. The technique of chromatography is based (in the difference in the rates at which the components of a mixture are absorbed in the suitable absorbent.

There are many types of chromatography :
(a) Column (absorption) Chromatography
(b) Thin layer chromatography
(c) Paper - chromatography
(d) High pressure liquid chromatography
(e) In-exchange chromatography
(f) Gas chromatography

Sedimentation and Decantation

This method is used when one component is a liquid and other is an insoluble. Insoluble solid, heavier than liquid, i.e, mud and water.
If muddy water is allowed to stand undisturbed for sometime in a beaker, the particles of earth (clay and sand) settle at the bottom. This process is called sedimentation. The clear liquid at the top can be gently transferred into another beaker. This process is known as decantation.