chile saltpeter
Though dinitrogen comprises 78% of the earth's atmosphere, it is not a very abundant element in the earth's crust. Nitrates are all very soluble in water so they are not widespread in the earth's crust, though deposits are found in a few desert regions. The largest is a 450–mile–long belt along the coast of Northern Chile, where NaNO3 (chile saltpeter) is found together with small amounts of KNO3, CaSO4 and NaIO3 under a thin layer of sand or soil. This provided the main source of nitrates prior to World war I. Synthetic processes were developed for the manufacture of nitrates from atmosphere dinitrogen.
Nitrogen in protien structure
Nitrogen is an essential constituent of proteins and amino acids. Nitrates and other nitrogen compounds are extensively used in fertilizers and explosives. Dinitrogen gas is used in large amounts as an inert atmosphere. This is used mainly in the iron and steel and other metallurgical industries, and in oil refineries for purging catalytic cracking vessels, re–forming vessels and pipes. Liquid nitrogen is used as a refrigerant. Large amounts of N2 are used in the manufacture of ammonia and calcium cyanamide.
N2 is obtained commercially by condensing air to the liquid state, and then fractionally distilling the liquid air. N2 has a lower boiling point than O2 and distils off first. Six industrial gases are obtained in this way. They are N2, O2, Ne, Ar, Kr and Xe.
Fractional distillation of liquid air for nitrogen
A cylinder of nitrogen is the usual source of N2 in the laboratory, but samples of the gas may be obtained by making ammonium nitrite and then warming it.
N2 is also obtained by oxidizing ammonia, for example with calcium hypochlorite, bromine water or CuO.
Small quantities of very pure N2 may be obtained by carefully warming sodium azide NaN3 to about 300°C. Thermal decomposition of NaN3 is used to inflate the air bags used as safety devices in some cars.
