Thursday, August 22, 2013

Application of Colloids

Some important applications of colloidal are as follows:-
1.      Rubber Plating
                  The negatively charged rubber particles from rubber sol are deposited on wares handles of different tools, rubber gloves, etc by electroplating.
2.      Sewage Disposal
                  Sewage water contains particles of dirt, rubbish etc which are of colloidal size carry and charge and therefore do not settle down easily. The particles can be removed by electrophoresis. Dirty water is passed through a tunnel fitted with metallic electrode which is maintained at high potential difference. The particles migrate to the oppositely charged electrode, lose their charge and are coagulated. The deposited matter is used as a manure and water left behind is used for irrigation.
3.      Cottrel Smoke Precipitator
                  Smoke is made free of colloidal particles by passing it through cottrel’s precipitator installed in the chimney of an industrial plant. It consists of two metal discs charged to a high potential. The charge on colloidal dust and carbon particles of smoke is neutralised and they are precipitated down while free gases come out through chimney.

4.      Formation of Delta
                  River water is a sort of colloidal solution of clay in water. Sea water on other hand, contains large number of dissolved salts and is a sort of electrolyte. When river water comes in contact with sea water, coagulation of colloidal particles occurs. These coagulated clay particles settle down at a point of contact and gradually river bed starts rising. This lead river water to adopt different course and ultimately results in the formation of delta.

5.      Leather Industry
                  In leather industry, the tanning of leather is based on the mutual coagulation of oppositely charged colloids. The animal skin is positively charged colloidal system containing albumin and geletin in the colloidal state. When treated with negatively charged colloidal system of tanin, present in barks of trees, wood leaves etc, a mutual coagulation of two oppositely charged sols take place. As a result, the surface of leather becomes harder.
6.      Dyeing Industry
                  Dyeing is essentially an adsorption of dye by the colloidal particles of mordant used. The clothes like those of cotton, wool, silk etc are colloidal in nature and Mordants used are also colloidal in nature. The mordants like Al(OH)3, SnCl2, tanin etc are readily adsorbed by fibres. This is another typical case of colloidal state of matter.
7.      Artificial Rain
                  Artificial rain is caused by spraying oppositely charged colloidal dust or sand particles over the clouds by aeroplane. The colloidal water particles of cloud gets neutralised and coagulation causes artificial rain.
8.      Purification of Water
                  The colloidal particles present in water can be precipitated by addition of small amount of alum (K2SO4 . Al2 (SO4)3 . 24 H2O). The Al3+ ions furnished by alum helps coagulation of impurities which are present in colloidal form.
9.      Distinction of Natural from Artificial Honey
                  Natural honey is also colloidal in nature. The distinction between two is made by  Ley’s Test. It consists of treating few drops of honey with ammonical AgNO3 solution. In case of pure honey, metallic silver produced assumes reddish yellow colour due to the traces of Albumin or ethereal oils, which acts as protective colloids. The dark yellow or greenish precipitate is formed with artificial honey.

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