Notes On Colloids Around Us - CBSE Class 12 Chemistry
Colloids play a very important role in nature, and in our daily life. The food, clothes, wooden furniture, houses the newspapers, are all largely composed of colloids. The sky is the empty space around the earth, and has no colour as such. It appears blue due to the scattering of blue light by the dust particles and the water suspended in the air. Sea water also looks blue for the same reason. The colloidal impurities in sea water scatter blue light. The Tyndall effect of scattering of light by colloids is responsible for the blue colour of the sky and sea water. Blood is a colloidal solution .Bleeding from a fresh cut can be stopped by applying a concentrated solution of ferric chloride or potash alum. Fog, mist and rain are all colloidal in nature. In winters, at night, the moisture in the air condenses on the surface of dust particles, forming tiny droplets. These droplets, being colloidal in nature, float in the air, forming mist or fog. Even clouds are colloidal systems. Clouds are aerosols consisting of small droplets of water suspended in air. Clouds are colloidal, carrying some electrical charge. Clouds can be made to cause rain by spraying oppositely charged colloidal dust or sand particles or precipitates of silver iodide over them. The neutralisation results in coagulation of the water droplets, which come down in the form of rain. This type of rain is called artificial rain. Cleansing action of soaps: Soap solutions are colloidal in nature. They remove the dirt and oil particles either by adsorption or by emulsifying the greasy matter sticking to cloth. Industrial applications of colloids: The most important industrial application of colloids is the Cottrell smoke precipitator. Smoke is a colloidal solution of solid particles such as carbon, arsenic compounds and dust. The Cottrell precipitator precipitates smoke on the principle of electrophoresis. Another application of coagulation of colloids is the purification of water. Precipitating these colloidal impurities can be carried out by adding certain electrolytes like potash alum or aluminium sulphate. Application of colloids is in medicines: Colloidal medicines are more easily assimilated by the body system as they can act over a large surface area. Therefore, they are more effective Some important sols that are commonly used as medicine are Argyrol, a silver metal sol used as an eye lotion, Colloidal antimony used for curing Kalaazar, and Colloidal gold used for inter-muscular injections. Application is in the leather tanning industry. Raw skin hides of animals contain positively charged colloidal particles. The principles of colloids and interface science are used for the successful formulation and manufacture of photographic products. Application of colloidal sols is in the rubber industry: Latex obtained from rubber trees is an emulsion consisting of negatively charged rubber particles in water. Rubber is obtained by the coagulation of latex. This coagulated mass is later subjected to vulcanisation, and is solid as rubber. Inks, paints, lubricants, synthetic plastics, cement, smoke screens are all colloidal solutions. Sewage disposal also makes use of the phenomenon of electrophoresis.

#### Summary

Colloids play a very important role in nature, and in our daily life. The food, clothes, wooden furniture, houses the newspapers, are all largely composed of colloids. The sky is the empty space around the earth, and has no colour as such. It appears blue due to the scattering of blue light by the dust particles and the water suspended in the air. Sea water also looks blue for the same reason. The colloidal impurities in sea water scatter blue light. The Tyndall effect of scattering of light by colloids is responsible for the blue colour of the sky and sea water. Blood is a colloidal solution .Bleeding from a fresh cut can be stopped by applying a concentrated solution of ferric chloride or potash alum. Fog, mist and rain are all colloidal in nature. In winters, at night, the moisture in the air condenses on the surface of dust particles, forming tiny droplets. These droplets, being colloidal in nature, float in the air, forming mist or fog. Even clouds are colloidal systems. Clouds are aerosols consisting of small droplets of water suspended in air. Clouds are colloidal, carrying some electrical charge. Clouds can be made to cause rain by spraying oppositely charged colloidal dust or sand particles or precipitates of silver iodide over them. The neutralisation results in coagulation of the water droplets, which come down in the form of rain. This type of rain is called artificial rain. Cleansing action of soaps: Soap solutions are colloidal in nature. They remove the dirt and oil particles either by adsorption or by emulsifying the greasy matter sticking to cloth. Industrial applications of colloids: The most important industrial application of colloids is the Cottrell smoke precipitator. Smoke is a colloidal solution of solid particles such as carbon, arsenic compounds and dust. The Cottrell precipitator precipitates smoke on the principle of electrophoresis. Another application of coagulation of colloids is the purification of water. Precipitating these colloidal impurities can be carried out by adding certain electrolytes like potash alum or aluminium sulphate. Application of colloids is in medicines: Colloidal medicines are more easily assimilated by the body system as they can act over a large surface area. Therefore, they are more effective Some important sols that are commonly used as medicine are Argyrol, a silver metal sol used as an eye lotion, Colloidal antimony used for curing Kalaazar, and Colloidal gold used for inter-muscular injections. Application is in the leather tanning industry. Raw skin hides of animals contain positively charged colloidal particles. The principles of colloids and interface science are used for the successful formulation and manufacture of photographic products. Application of colloidal sols is in the rubber industry: Latex obtained from rubber trees is an emulsion consisting of negatively charged rubber particles in water. Rubber is obtained by the coagulation of latex. This coagulated mass is later subjected to vulcanisation, and is solid as rubber. Inks, paints, lubricants, synthetic plastics, cement, smoke screens are all colloidal solutions. Sewage disposal also makes use of the phenomenon of electrophoresis.

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