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Nitrogen

by Ron Kurtus (30 November 2007)

Nitrogen is a colorless, odorless gas that makes up 78% of the Earth's atmosphere. It is chemically inactive and must be forced to combine with other materials through the use of high pressure, high temperature and special catalysts. Nitrogen is found naturally in some mineral deposits, in the soil and in organic compounds. Nitrogen is usually prepared by removing the oxygen from air, but it also can be formed from some chemical reactions.

Questions you may have include:

• What are the properties of nitrogen?
• Where is nitrogen found in nature?
• How is nitrogen prepared?

This lesson will answer those questions. There is a mini-quiz near the end of the lesson.

Properties of nitrogen

The atomic number of nitrogen is 7, meaning it has 7 protons in its nucleus. Its atomic weight or atomic mass is approximately 14 for the most common isotope of nitrogen (¹⁴N) that makes up 99.6% of the nitrogen found in nature. The other common isotopes of nitrogen are ¹⁵N, which is a stable isotope and ¹³N, which is unstable and has a half-life of only 10 minutes.

(See Isotopes for more information on that subject.)

Nitrogen is a colorless, tasteless, odorless gas that somewhat less dense than air and slightly soluble in water. At a lows temperature and under pressure, it may be converted into liquid nitrogen.

Chemical properties

Under ordinary conditions, nitrogen is a highly inactive element. It neither burns nor supports combustion. However, high temperature, high pressure and catalysts are effective in forcing nitrogen into chemical combinations with other elements.

For example, under high heat conditions nitrogen can be made to combine with oxygen to form nitric oxide. Lightning often creates nitric oxide by heating the air to extreme temperatures. Automobile engines also create nitric oxide, which is a major compound in smog:

N₂ + O₂ → 2NO

Ammonia is a result of forcing nitrogen to combine with hydrogen:

N₂ + 3H₂ → 2NH₃

Nitrogen can also be forced to combine with some of the active metals to form nitrides. For example, combining nitrogen with aluminum under the right conditions results in aluminum nitride:

2Al + N₂ → 2AlN

Occurrence of nitrogen in nature

Nitrogen occurs naturally in many areas.

• The most obvious is that it makes up 78% of the Earth's atmosphere.
• It is found combined in a large number of natural compounds, such as saltpeter or sodium nitrite (NaNO₃).
• Nitrogen is present in soils, in the form of nitrates, nitrites, and ammonium salts. These compounds are also often used to fertilize the soil.
• Nitrogen is found in proteins and other organic compounds that are present in meat, egg whites, and vegetables.

Preparation of nitrogen

There are several methods to prepare nitrogen from air, both in the laboratory and commercially. Nitrogen can also be prepared from nitrogen compounds.

Laboratory methods from air

One method of creating nitrogen from air is oxidize some material to rid the air of the oxygen in it. Burning carbon-based materials does not work, since the result is Carbon Dioxide gas (CO₂). The idea is to get rid of most gases that are not nitrogen.

Burning phosphorus or allowing iron filings to oxidize in a closed container results in nitrogen and a small amount of other gases from the air in the enclosed chamber. The oxygen has been removed.

Another method is to pass a air over hot copper gauze in an enclosed container. The copper combines with the oxygen, forming copper oxide and leaving nearly pure nitrogen.

2Cu + O₂ + N₂ → 2CuO + N₂

Commercial method from air

A major commercial method of preparing nitrogen is from liquid air. Air is first liquefied by being subjected to extremely high pressure and low temperatures. The liquid air is then allowed to heat up and its gases allowed to evaporate. Nitrogen, which has a lower boiling point than oxygen, escapes first and is then collected.

Using nitrogen compounds

To prepare pure nitrogen in the laboratory, a mixture of ammonium chloride (NH₄Cl) and sodium nitrite (NaNO₂) is heated. The first product that is formed is ammonium nitrite (NH₄NO₂). This compound is very unstable, and breaks up into nitrogen and water. Caution must be used in this experiment to avoid explosive reactions.

NH₄Cl + NaNO₂ → NH₄NO₂ + NaCl → N₂+ 2H₂ + NaCl

Note: Often chemical equations will use an upward arrow↑to indicate that a resulting material is a gas. For example, N₂↑.

Nitrogen gas can also be prepared by heating a water solution of ammonium nitrite (NH₄NO₃).

H₂O + NH₄NO₃ → N₂ + 3H₂O

Summary

Nitrogen is a colorless, odorless gas that is chemically inactive and must be forced to combine with other materials. It makes up 78% of the Earth's atmosphere and is found naturally that in some mineral deposits, in the soil and in organic compounds. Nitrogen is usually prepared by removing the oxygen from air, but it also can be formed from some chemical reactions.

Answers to Readers' Questions

Resources

The following resources provide information on this subject:

Websites

Los Alamos National Laboratories - Chemistry site

Nitrogen Cycle in Biology

Chemistry Resources

Books

Top-rated books on Chemistry

Miscellaneous

Mini-quiz to check your understanding

1. How is the amount of nitric oxide (NO) created from automobile engines reduced?

2. Why is nitrogen important to us?

3. What is the most common method of preparing nitrogen?

If you got all three correct, you are on your way to becoming a Champion in Chemistry. If you had problems, you had better look over the material again.

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