Air is made up of different gases, such as oxygen, nitrogen, and carbon dioxide. How would you best describe these three components of air?
Answers
the rare gases
Except for helium, which is mostly extracted from natural gas, oxygen, nitrogen and the other rare gases are extracted from the air that makes up Earth's atmosphere. Unlike the sources of some chemicals there are therefore no concerns about the depletion of this resource and if a sample of air is used to produce one of the gases, there are no problems about venting the 'waste gases' back into the atmosphere.
The ready availability of oxygen and its reactivity with many other elements means that it is used during the production of many other chemicals, whereas some of the uses of nitrogen and the rare gases depend on their inertness.
Uses
Oxygen
The largest user of oxygen is the steel industry. It is also used in the manufacture of other metals, notably copper and lead. It is more economic to use pure oxygen, or oxygen-enriched air, rather than air as this increases the reaction rates and means that smaller chemical plants can be used. Further it makes it easier to ensure that no gases such as sulfur dioxide are lost and pollute the atmosphere.
The gas is also used in the manufacture of many chemicals including nitric acid, hydrogen peroxide, epoxyethane and chloroethene (vinyl chloride), the precursor to PVC.
Among its other uses is the burning off of carbon deposited on the fluid catalyst used in the catalytic cracking of gas oil
A growing use for oxygen is in treating sewage and effluent from industry. Polluted rivers and lakes can be cleaned by dissolving oxygen gas directly into the water to encourage a better ecological balance. It is used, for example, in fish farming to provide this balance.
It is also used, with sodium hydroxide, to bleach paper pulp as an alternative to chlorine dioxide or sodium chlorate(I) (sodium hypochlorite).
Nitrogen
Nitrogen is used to make ammonia. It is also widely used to provide an inert atmosphere, a process known as 'blanketing', principally to exclude oxygen. For example, nitrogen is used in this way in food packaging, glass making, and semiconductor manufacture. It is also used to purge out pipes prior to welding (for example, oil pipes) to ensure that no flammable vapours are left behind.
Liquid nitrogen is being increasingly used to refrigerate food during transportation. Medical samples containing, for example blood, viruses for vaccinations and semen, can be stored for long periods if kept cool in liquid nitrogen.

Figure 1 Oil tankers are purged with nitrogen to prevent explosions during welding and other
maintenance. The photo is of the Omala moored in Rotterdam, the Netherlands.
By kind permission of Danny Cornelissen (Wikimedia Commons).
Rare gases
Liquid helium, with its very low boiling point of 4 K, has become very important in cooling superconductor magnets, used, for example, in MRI scanners for medical diagnosis. The magnets generate much heat and helium is the first choice as it has the lowest boiling point of any liquid. Its inertness is fundamental to its other major uses, for example, to provide an inert atmosphere when welding metals (to prevent metals reacting with air to form oxides and nitrides). It is also used to purge gas from tanks which have contained fuels such as liquid hydrogen.
It also provides an inert atmosphere during the manufacture of high value materials such as optical fibres.
Due to its low density, helium is used for weather balloons and airships. It is also used in combination with oxygen to produce specialised breathing mixtures for divers. These mixtures are better than nitrogen-oxygen mixtures for prolonged diving as the blood will absorb only a limited amount of helium whereas with nitrogen, its concentration can build up to dangerous levels over a prolonged period.
Helium is also used in eximer lasers and helium-neon lasers that are used for bar code scanners.