Nitrogen being a neutral gas that does not affect the color of indicators.
(ii) Combustibility
It is neither combustible not a supporter of combustion.
(iii) Combination with elements
Nitrogen does not easily combine with other elements under ordinary conditions. A molecule of nitrogen is diatomic. These two atoms have combined by mutually sharing three pairs of electrons (Fig.12.7).
The triple bond formed between the atoms is so strong, that a large amount of energy is needed to break this bond. Hence special conditions such as temperature, pressure, catalyst, promoters, high voltage etc. may be needed to make nitrogen combine with other elements.
a) With hydrogen
Nitrogen combines with hydrogen in presence of electric sparks to form ammonia. Usually ammonia is obtained by treating a 3:1 mixture (by volume) of hydrogen and nitrogen at about 450oC, and a pressure of 200 to 1000 atm, in the presence of finely divided iron as catalyst and molybdenum as promoter.
Remember :
Promotor is a substance, added along with a catalyst to increase the efficiency of the catalyst. Promoters are also called activators.
b) With oxygen
Nitrogen combines with oxygen only in presence of an electric arc at a temperature of 3000 - 5000oC to form nitric oxide. Also when lightning takes place in the sky, electric sparks of high voltage are formed that make nitrogen and oxygen of the atmosphere reactive enough to form nitric oxide.
c) With metals
Red hot or burning magnesium, calcium and aluminium combine with nitrogen to form their respective nitrides (Fig.12.8).
Remember :
A binary compound of an element with nitrogen is called a "nitride".
When these nitrides react with hot water, they yield their respective hydroxides and ammonia.
d) With calcium carbide
When calcium carbide is heated in presence of nitrogen at 800oC to 1000oC it gives calcium cynamide an important fertilizer. The commercial name of calcium cynamide is nitrolim.
