Chemistry

The preparation of aerosols can be as simple as sneezing (which produces an aerosol). Laboratory and commerical methods make use of several techniques. Chemical precipitation sometimes results in a colloid. A precipitate (e.g. silver iodide) already formed may be dispersed by the addition of a peptizing agent (e.g. potassium iodide). Clays may be peptized by alkalis, the OH⁻ ion being the active agent. Emulsions are normally prepared by shaking the two components together, although some kind of emulsifying agent has to be used in order to stabilize the product. This emulsifier may be a soap (a long chain fatty acid), a surfactant (Section 23.11), or a lyophilic sol that forms a protective film around the dispersed phase. In milk, which is an emulsion of fats in water, the emulsifying agent is casein, a protein containing phosphate groups. That casein is not completely successful in stabilizing milk is apparent from the formation of cream on the surface : the dispersed particles coalesce into oily droplets which float to the surface. Aerosols are formed when a spray of liquid is torn apart by a jet of gas. The dispersal is aided if a charge is applied to the liquid, for then the electrostatic repulsions blast the jet apart into droplets. This procedure may also be used to produce emulsions, for the charged liquid phase may be squirted into another liquid. Colloids are often purified by dialysis. As in the discussion of Donnan effect membrane (e.g. cellulose) is selected which is permeable to solvent and ions, but not to the colloidal particles. Dialysis is very slow, and is normally accelerated by applying an electric field and making use of the charge carried by many colloids; the technique is then called electrodialysis.

Carbon compounds are broadly classified into two main categories : 1. Organic compounds : These contain carbon and hydrogen and may also include other elements like oxygen, nitrogen, sulfur etc. They include hydrocarbons (such as methane, ethane, propane), alcohols, acids and polymers (like plastics, rubber). Organic compounds are essential in biological systems, forming the basis of molecules like proteins, carbohydrates, lipids and nucleic acids (DNA and RNA). They are also used widely in industries for example, in the manufacture of fuels, dyes, medicines, pesticides and plastics. 2. Inorganic compounds : These include compounds like Carbon dioxide (CO2), Carbon Monoxide (CO), carbonates (such as calcium carbonate in limestone) and bicarbonates. These compounds are vital in geological and environmental processes, such as the carbon cycle, which maintains the balance of carbon in the eco-system. Carbon compounds exhibit various properties, most organic compounds have low melting and boiling points, are generally flammable and more soluble in organic solvents rather than water. This makes them useful as fuels and industrial solvents. Their diversity and reactivity make them a central part of the field of chemistry, particularly in synthetic and pharmaceutical industries.

Carbon compounds are broadly classified into two main categories : 1. Organic compounds : These contain carbon and hydrogen and may also include other elements like oxygen, nitrogen, sulfur etc. They include hydrocarbons (such as methane, ethane, propane), alcohols, acids and polymers (like plastics, rubber). Organic compounds are essential in biological systems, forming the basis of molecules like proteins, carbohydrates, lipids and nucleic acids (DNA and RNA). They are also used widely in industries for example, in the manufacture of fuels, dyes, medicines, pesticides and plastics. 2. Inorganic compounds : These include compounds like Carbon dioxide (CO2), Carbon Monoxide (CO), carbonates (such as calcium carbonate in limestone) and bicarbonates. These compounds are vital in geological and environmental processes, such as the carbon cycle, which maintains the balance of carbon in the eco-system. Carbon compounds exhibit various properties, most organic compounds have low melting and boiling points, are generally flammable and more soluble in organic solvents rather than water. This makes them useful as fuels and industrial solvents. Their diversity and reactivity make them a central part of the field of chemistry, particularly in synthetic and pharmaceutical industries.