CHEMICAL ACTION OF OXYGEN
(a) Upon Substances
Effect of air upon iron and wood
Upon some substances oxygen acts at ordinary temperature. Iron becomes covered with rust when exposed to air and moisture. Wood and other vegetable and animal substances undergo slow decomposition when exposed to the air. This is partly due to the action of oxygen at ordinary temperature.
Pure oxygen aids combustion
A splinter of wood will burn brilliantly in a jar of pure oxygen, and much more rapidly than in common air. Pure oxygen gas will cause many substances to burn which will not burn in air. Iron can be burned in pure oxygen, leaving only a reddish powder.
Formation of iron-rust
When iron rusts the carbon dioxid and water vapor combine chemically with the iron, and form what is known as a basic hydroxid or carbonate of iron. The process is somewhat complex. When iron burns in oxygen a red powder is formed—ferric oxid, Fe2O3. Iron dissolves in water, or moisture from the air containing carbonic acid, forming acid ferrous carbonate—
Fe + 2H2CO3 = FeH2(CO3)2 + H2
Iron + Carbonic acid = Acid ferrous carbonate + Hydrogen
This acid ferrous carbonate, on drying or further oxidation, is converted into iron-rust. If we represent iron-rust by the formula Fe2O3. 2Fe(OH)3, the equation is as follows: