Thursday, December 24, 2009

General Chemistry Notes-4


Calcination is heating strongly in the absence of air. Roasting is heating in the excess of air . Smelting, also called autoreduction, involves reduction of ores, usually oxides at elevated temperatures.


It is difficult to remove the earthy matter called gangue which contaminates an ore. This is done by adding to ore a substance called flux. Flux combines with gangue to form a molten product called slag, which can be easily removed.

An alloy is a mixture of two or more metals and is homogeneous in nature. For example Brass (Copper, Zinc), Bronze ( Copper, Tin) and Gun Metal ( Copper, Tin and Zinc) are examples of alloys.

An amalgam is a solution of metal in mercury. Sodium amalgam is used a reducing agent. Tin amalgam is used for making mirrors. Cadmium and Gold amalgam are used in dentistry.

A few elements like arsenic, Antimony, Boron, Silicon and Germanium behave both like metals and non-metals. These are called metalloids.

The five main causes of air pollution are carbon monoxides, nitrogen oxides, hydrocarbons and sulphur oxides. Transportation sources are responsible for 74% of all carbon monoxide emissions. Use of Catalytic converter in two stages helps in eliminating pollutants from exhaust gases before they are discharged into atmosphere. In the first stage converter, Nitrogen Oxide is converted to Nitrogen and Ammonia in the presence of finally divided Platinum as a catalyst. In the second stage coverter, Hydrocarbons and carbon monoxide are completely oxidized to water and carbon dioxide in the presence of Platinum catalyst. Unleaded gasoline should be used as Platinum can be poisoned by the lead.

Much of Nitrogen Oxides and Sulphur Oxides entering into the atmosphere are converted into Nitric acid and Sulphuric acid. This will generate precipitation known as acid rain.

Urea is used as a fertilizer. DDT ( Dichloro-Di-Phenyl Trichloro Ethane) and BHC ( Benzene HexaChloride) , Melathion and parathion are used as pesticides. Zinc Phosphate and Barium Carbonate are used as rodenticides. Bordeaux Mixture ( copper Sulphate + Lime + Water) are used as fungicides.