Nitrogen

Author: Robert Husted, Mollie Boorman

History

(L. nitrum, Gr. Nitron, native soda; and genes, forming) Nitrogen was discovered by chemist and physician Daniel Rutherford in 1772. He removed oxygen and carbon dioxide from air and showed that the residual gas would not support combustion or living organisms. At the same time there were other noted scientists working on the problem of nitrogen. These included Scheele, Cavendish, Priestley, and others. They called it "burnt" or "dephlogisticated air", which meant air without oxygen.

The Element

The French chemist Antoine Laurent Lavoisier mistakenly named nitrogen azote, meaning without life. However, nitrogen compounds are found in foods, organic materials, fertilizers, poisons, and explosives. Nitrogen, as a gas is colorless, odorless, and generally considered an inert element. As a liquid (boiling point = minus 195.8°C), it is also colorless and odorless, and is similar in appearance to water.

Sources

Nitrogen gas (N₂) makes up 78.1% of the Earth’s air, by volume. The atmosphere of Mars, by comparison, is only 2.6% nitrogen. From an exhaustible source in our atmosphere, nitrogen gas can be obtained by liquefaction and fractional distillation. Nitrogen is found in all living systems as part of the makeup of biological compounds.

Nitrogen gas can be prepared in the lab by heating a concentrated water solution of ammonium nitrite (NH₄NO₂). This reaction is a two step process: First, the ammonium nitrite disproportionates into ammonia and nitrous acid which react in a second step to nitrogen and water:

NH₄NO₂ NH₃ + HNO₂
NH₃ + HNO₂ N₂ + 2 H₂O

Nitrogen Compounds and Nitrogen in Nature

Sodium nitrate (NaNO₃) and potassium nitrate (KNO₃) are formed by the decomposition of organic matter with compounds of these metals present. In certain dry areas of the world these saltpeters are found in quantity and are used as fertilizers. Other inorganic nitrogen compounds are nitric acid (HNO₃), ammonia (NH₃), the oxides (NO, NO₂, N₂O₄, N₂O), cyanides (CN^-), etc.

The nitrogen cycle is one of the most important processes in nature for living organisms. Although nitrogen gas is relatively inert, bacteria in the soil are capable of “fixing” the nitrogen into a usable form (as a fertilizer) for plants. In other words, Nature has provided a method to produce nitrogen for plants to grow. Animals eat the plant material where the nitrogen has been incorporated into their system, primarily as protein. The cycle is completed when other bacteria convert the waste nitrogen compounds back to nitrogen gas. Nitrogen is crucial to life, as it is a component of all proteins.

Ammonia

Ammonia (NH₃) is the most important commercial compound of nitrogen. It is produced by the Haber Process. Natural gas (methane, CH₄) is reacted with steam to produce carbon dioxide and hydrogen gas (H₂) in a two step process. Hydrogen gas and nitrogen gas reacted via the Haber Process to produce ammonia. This colorless gas with a pungent odor is easily liquefied (in fact, the liquid is used as a nitrogen fertilizer). Ammonia is also used in the production of urea, NH₂CONH₂, which is used as a fertilizer, used in the plastic industry, and used in the livestock industry as a feed supplement. Ammonia is often the starting compound for many other nitrogen compounds.