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Nitrogen

Nitrogen is one of the gases that make up the atmosphere and has the molecular formula, N₂.   

(1). From the atmosphere. Air is composed mainly of oxygen, carbon- dioxide and nitrogen. Both oxygen and carbon(IV) oxide can be removed from a volume of air, leaving behind nitrogen, by passing the volume of air into either sodium hydroxide or calcium hydroxide solution (to absorb the CO₂ content), and then passing the resulting gas through a mass of heated copper (to remove the oxygen content - copper reacts with oxygen when heated to give CuO).

The gas left is nitrogen, with some noble gases (about 1% by volume).

Note: nitrogen obtained from air is not pure - it contains the noble gases of the air, hence it is denser than pure nitrogen .

Alternatively , nitrogen can be obtained from the atmosphere by absorbing both carbon(IV) oxide and oxygen together by shaking air with a solution of benzene -1,2,3- triol in sodium hydroxide solution.

Oxygen is absorbed by benzene -1,2,3 triol to form an oxidation product of itself, while carbon(IV)oxide is absorbed by sodium hydroxide solution.

(2). Preparation of nitrogen by action of heat on:

(a). Ammonium dioxonitrate(III) solution - NH₄NO₂ readily decomposes slowly on slight warming at ordinary temperature to liberate nitrogen.

Note: NH₄NO₂ is not kept in stock because it will decompose. Also, it is not advisable to heat NH₄NO₂ solution directly, because the reaction might be explosive.

To produce nitrogen by this method, a mixture of suitable substances which would produce NH₄NO₂, and subsequently produce the required nitrogen are warmed slightly.

Example, a mixture of dioxonitrate(III) salt and an ammonium salt are warmed to initially produce ammonium dioxonitrate(III), NH₄NO₂, which immediately decomposes to give the desired nitrogen.

It is common to use sodium dioxonitrate(III) solution and ammonium chloride solution.

NaNO_2(aq) + NH₄Cl_(aq) → NH4NO_2(aq) + NaCl_(aq)

Then NH₄NO_2(aq) → N2_(g) + 2H₂O_(l)

(b). Ammonium dichromate(VI), (NH₄)₂Cr₂O₇

(3). The action of chlorine on excess ammonia.

3Cl_2(g) + 8NH_3(g) → N_2(g) + 6NH4Cl_(s)

(4). By passing ammonia gas over heated copper(II)oxide.

2NH_3(g) + 3CuO_(s) → 3Cu_(s) + 3H₂O_(g) + N_2(g)

(5). By reduction of oxides of nitrogen by heated copper.

Example, 2Cu_(s) + 2NO_(g) → 2CuO_(s) + N_2(g)

(6). Production of nitrogen from liquid air:

The process of liquefying air and obtaining nitrogen is explained here: What is Air?

Properties of Nitrogen

Nitrogen shows the following properties:

Physical Properties

1. Nitrogen is a colourless and tasteless gas.

2. It is a little lighter than air).

3. It is only slightly soluble in water.

4. It has a boiling point of 77 K at 1 atmosphere

5. It has a freezing point of 63 K.

Chemical properties

The nitrogen atom has two s and three p electrons in its outermost shell. Three pairs of shared electrons bond the two atoms together in the N₂ molecule:

:N:::N:

The great strength of this triple bond is responsible for the stability of the N₂ molecule and the consequent relative inertness of elementary nitrogen.

The dissociation of 1 mole of N₂ molecules involves the absorption of very high energy (171 kcal). The same quantity of energy is released when 2 moles of nitrogen atoms form 1 mole of N₂ molecules.

This is the basic reason for the instability of many nitrogen compounds. Some of the compounds are so unstable that they decompose with explosive violence.

Most chemical explosives are nitrogen compounds and elementary nitrogen is a product of their decomposition. Some reactions of nitrogen are:

1. Nitrogen combines directly with certain metals, such as Ca, Al, Mg and Fe at very high temperatures and pressures.

Example, Magnesium when red hot combines with nitrogen to form a magnesium nitride.

3Mg_(s) + N_2(g) → Mg₃N_2(s)

Note: when water is added to the nitride, it hydrolysis to liberate ammonia.

Mg₃N_2(s) + 6H₂O_(l) → 3Mg(OH)_2(s) + 2NH_3(g)

2. Nitrogen reacts with hydrogen and oxygen at high temperatures and pressures. With hydrogen - the reaction is reversible, and a catalyst is used.

Ammonia is produced.

N2(g) + 3H2(g)

2NH3(g)

With oxygen - at very high temperatures (about 2000^oC), nitrogen reacts with oxygen to form nitrogen(II)oxide.

N_2(g) + O_2(g) → 2NO_(g)

Note: this reaction is also given during thunder and lightening.

Nitrogen is not reactive. That is, it is inert at ordinary temperatures. Hence, it becomes extremely difficult to test chemically.

However, a certain gas can be confirmed to be nitrogen by eliminating other possibilities, such as: combustion (nitrogen does not burn or support combustion); action with lime water (nitrogen does not show any effect); with litmus paper and with acidified KMnO₄ (nitrogen does not show any effect).

Nitrogen can be used in the following ways:

1. For the manufacture of synthetic ammonia - this is the single largest use for nitrogen.

2. For the making of calcium cyanamide.

3. To provide inert atmosphere as a protection against oxidation for processes such as the canning of foods.