Short Notes:

Colloids are mixtures of substances that have particles of liquids, solids, or gas evenly distributed throughout. The size of the particles is the defining characteristic of a colloid. Depending on their composition, colloids have different names. If the particles are gas and the medium in which they are suspended is liquid or solid, the colloid is called a foam. One example is air that has been beaten into cream to form whipped cream. A dispersal of liquid particles within a liquid is known as an emulsion. An example of an emulsion is homogenized milk. Solids within a liquid or gas are sols, such as aerosols or, if the liquid is water, hydrosols. Colloids include such naturally occurring substances as egg whites, blood, and fog. Everyday man-made colloids include mayonnaise, jelly, foam rubber, and paints. Chemists study the many interesting properties of colloids, including the unique way in which they scatter light or in which they can be filtered. This is known as the Tyndall effect - light shining through a colloid is scattered in bands. The effect occurs because particles absorb and re-emit light in all directions.