Preparation of Nitrogen and Chemical Properties of Nitrogen

Nitrogen, N₂, is prepared in the laboratory by any of the following reactions: From ammonium dioxonitrate(III), ammonium heptaoxodichromate(VI), ammonia and dinitrogen(I) oxide.

Preparation from ammonium dioxonitrate(III)

Ammonium dioxonitrate(III), NH₄NO₂, is the most popular choice for the preparation of nitrogen as it decomposes in a fast pace to produce nitrogen and steam. But ammonium dioxonitrate(III) is unstable. It decomposes exothermically so that an explosion might occur during the preparation process. Small wonder nitrogen is prepared by first heating a mixture of ammonium chloride, NH₄Cl, and sodium dioxonitrate(III) in a ratio of 5 : 7 to form ammonium dioxonitrate(III), NH₄NO₂, and sodium chloride, NaCl.

NaNO₂(aq) + NH₄Cl(aq) → NH₄NO₂(aq) + NaCl(aq)

The amonium chloride then decomposes swiftly to form nitrogen and steam.

NH₄NO₂(aq) → N₂(g) + 2H₂O(l)

Preparation from ammonium heptaoxodichromate(VI)

Here, ammonium heptaoxodichromate(VI), (NH₄)₂Cr₂O₇, is heated to decomposition so that nitrogen is formed with water and chromate(III) oxide, Cr₂O₃.

(NH₄)₂Cr₂O₇(s) → N₂(g) + Cr₂O₃(s) + 4H₂O(l)

Preparation from ammonia

Nitrogen is produced when ammonia, NH₃, is treated with hot copper(II) oxide. Here, the hot copper(II) oxide, CuO, serves as an oxidizing agent that oxidizes the ammonia to nitrogen gas, N₂, as it is reduced to copper metal, Cu.

2NH₃(g) + 3CuO(s) → 3Cu(s) + 3H₂O(g) + N₂(g)

Preparation from dinitrogen(I) oxide

A reduction reaction is used in this case to produce nitrogen. Dinitrogen(I) oxide is reduced to nitrogen when passed over red-hot copper as the copper is itself oxidised to copper(II) oxide, CuO.

N₂O(g) + Cu(s) → CuO(s) + N₂(g)

Nitrogen is about 78% by volume of the atmosphere, as such it's abundant in air so that it is prepared industrially by the fractional distillation of liquid air. Other constituents of the air are can be removed by specific means that include the removal of carbon(IV) oxide by passing the air through lime water, and the oxygen by passing the air through heated copper turnings. Otherwise, the oxygen gas can be liquefied with the air and remain as a component of the residual air once the nitrogen is separated as it has a lower boiling point of -183°C.

Gaseous air free of carbon(IV) oxide is subjected to compression and cooling to make liquefied air. The liquefied air is then subjected to distillation where the nitrogen gas is evolved at -196°C at standard pressure. Nitrogen produced by liquefaction is stored in steel cylinders as liquid or compressed nitrogen.

Nitrogen is a member of group 5 of the periodic table with five valence electrons. It forms a stable octet structure by entering into covalent bonds. The formation of a diatomic molecule with triple bond, N≡N, is an example of how it forms a covalent bond. Nitrogen has oxidation states that vary from -3 to +5 in different compounds. For example, nitrides, N^3-, are formed from the direct combination of nitrogen with group 1 and group 2 metals.

Reaction with metals

Nitrogen form nitrides with highly electropositive metals to form nitrides. For example, red-hot magnesium undergoes a direct combination reaction with nitrogen to form magnesium nitride.

3Mg(s) + N₂(g) → Mg₃N₂(s)

The magnesium nitride so formed is readily hydrolysed to ammonia gas and magnesium hydroxide, Mg(OH)₂, when warmed.

(warm) Mg₃N₂(s) + 6H₂O(l) → 3Mg(OH)₂(s) + 2NH₃(g)

Reaction with non-metals

Nitrogen forms small amount of nitrogen(II) oxide by direct combination with oxygen at a temperature of about 2000°C or in the presence of a high voltage electric spark.

N₂(g) O₂(g) → 2NO(g)

This is a very important reaction in that, it occurs in nature where lightening flashes provide the electric spark for the reaction.