Inert gases

An inert gas is a gas which does not undergo chemical reactions under a set of given conditions. The noble gases often do not react with many substances. Inert gases are used generally to avoid unwanted chemical reactions degrading a sample. These undesirable chemical reactions are often oxidation and hydrolysis reactions with the oxygen and moisture in air. The term inert gas is context-dependent because several of the noble gases can be made to react under certain conditions.

Purified argon and nitrogen gases are most commonly used as inert gases due to their high natural abundance (78% N₂, 1% Ar in air) and low relative cost.

Unlike noble gases, an inert gas is not necessarily elemental and is often a compound gas. Like the noble gases the tendency for non-reactivity is due to the valence, the outermost electron shell, being complete in all the inert gases. This is a tendency, not a rule, as noble gases and other "inert" gases can react to form compounds.

The inert gases are obtained by fractional distillation of air. For specialized applications, purified inert gas may be produced by specialized generators on-site. They are often used aboard chemical tankers and product carriers (smaller vessels). Benchtop specialized generators are also available for laboratories.

Because of the non-reactive properties of inert gases they are often useful to prevent undesirable chemical reactions from taking place. Food is packed in inert gas to remove oxygen gas. This prevents bacteria from growing. Chemical oxidation by oxygen in air is avoided. An example is the rancidification of oil. In food packaging, inert gases are used as a passive preservative, in contrast to active preservatives like sodium benzoate (an antimicrobial) or BHT (an antioxidant).

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