Ni­tro­gen is an el­e­ment in the 15ᵗʰ group (un­der the new clas­si­fi­ca­tion) of the sec­ond pe­ri­od of the Pe­ri­od Ta­ble. It is en­coun­tered in na­ture in the form of two iso­topes (atoms with iden­ti­cal atom­ic num­bers, but dif­fer­ent mass num­bers) – ni­tro­gen with the mass num­bers 14 and 15. Ni­tro­gen com­pris­es around 78% of the vol­ume of the air. This gas is one of the most abun­dant on Earth.

Phys­i­cal prop­er­ties and ob­tain­ing ni­tro­gen

By its phys­i­cal prop­er­ties, ni­tro­gen is a col­or­less gas with­out smell or taste. The boil­ing point of ni­tro­gen is -195.75 ᵒC (-320.35 ᵒF). The gas is chem­i­cal­ly in­ert. In the lab­o­ra­to­ry, ni­tro­gen is ob­tained by the de­com­po­si­tion of am­mo­ni­um ni­trate NH₄NO₂:

NH₄NO₂ = N₂ + 2H₂O (the ves­sel must first be heat­ed, then cooled, as the process is exother­mic – it takes place with the re­lease of heat, up to 335 kJ). The ni­tro­gen re­leased con­tains im­pu­ri­ties – ni­tro­gen and am­mo­ni­um ox­ides.

Molec­u­lar ni­tro­gen can also be ob­tained with the ther­mal de­com­po­si­tion of am­mo­ni­um and ni­tro­gen (I) ox­ide:

1. 2NH₃ = N₂ + 3H₂;

2. 2N₂O = 2N₂ + O₂.

In in­dus­tri­al con­di­tions, ni­tro­gen is ob­tained by dis­till­ing liq­ue­fied air. Ni­tro­gen dis­plays a con­sid­er­able num­ber of ox­i­da­tion states, from -3 to +5.

Com­pounds with an ox­i­da­tion state of ni­tro­gen of -3

The 2 most com­mon types of com­pounds in which the ox­i­da­tion state of ni­tro­gen is -3 is am­mo­ni­um and am­mo­ni­um salt (or am­mo­ni­um hy­drox­ide NH₄OH).

Am­mo­ni­um

The two most com­mon meth­ods of ob­tain­ing am­mo­ni­um are in the lab­o­ra­to­ry and in­dus­tri­al­ly:

1. In­dus­tri­al­ly – 3H₂ + N₂ = 2NH₃ (in harsh con­di­tions at high pres­sure and tem­per­a­ture, and in the pres­ence of a cat­a­lyst);

2. In the lab­o­ra­to­ry – Ca(OH)₂ + 2N­H₄­Cl = 2NH₃ + 2H₂O + Ca­Cl₂.

The main prop­er­ties of am­mo­ni­um are the fol­low­ing:

• NH₃ + HCl = NH₄­Cl (re­ac­tion with acids leads to the for­ma­tion of am­mo­ni­um salts);

• 2NH₃ + AgCl = [Ag(NH₃)₂]Cl (re­ac­tion with salts of heavy met­als leads to for­ma­tion of com­plex­es; in this case sil­ver (I) di­amine chlo­ride forms);

• 4NH₃ + 3O₂ = 2N₂ + 6H₂O (com­bus­tion re­ac­tion);

• 4NH₃ + 5O₂ = 4NO + 6H₂O (re­ac­tion of cat­alyt­ic ox­i­da­tion in the pres­ence of plat­inum with heat­ing);

• 2NH₃ + CuO = N₂ + 3Cu + 3H₂O (re­duc­tion re­ac­tion of cop­per from its ox­ide, car­ried out with heat­ing).

Am­mo­ni­um salts

Am­mo­ni­um salts are sol­id crys­talline sub­stances. You can de­tect the pres­ence of am­mo­ni­um ions in a salt by adding an al­ka­li to it:

NH₄­Cl + KOH = NH₃ + NaCl + H₂O (the am­mo­ni­um re­leased in the re­ac­tion has a spe­cif­ic smell; be­cause it is a base lit­mus pa­per turns blue when it is held up to the re­ac­tion flask);

Am­mo­ni­um salts can also de­com­pose un­der ther­mal im­pact. The pre­cise prod­ucts of re­ac­tion de­pend on the com­po­si­tion of the ini­tial salt:

• (NH₄)₂SO₄ = NH₃ + NH₄H­SO₄;

• NH₄NO₃ = N₂O + 2H₂O;

• NH₄­Cl = NH₃ + HCl.

Oth­er­wise, the prop­er­ties of am­mo­ni­um salts re­peat the prop­er­ties of oth­er salts sol­u­ble in wa­ter.

Prop­er­ties of ni­tro­gen with an ox­i­da­tion state of 0

As a sim­ple sub­stance, ni­tro­gen is an in­ert di­atom­ic gas. It en­ters into many re­ac­tions only when heat­ed:

• re­ac­tion with met­als with heat­ing (apart from lithi­um, which it re­acts with at room tem­per­a­ture):

3Ca + N₂ = Ca₃N₂;

6Li + N₂ = 2Li₃N;

• re­ac­tion with acety­lene:

С₂Н₂ + N₂ = 2HCN (takes place in a con­densed dis­charge);

Liq­uid ni­tro­gen

• re­ac­tion with hot coal:

2C + N₂ = (CN)₂ (di­cyanogen forms);

• re­ac­tion with boron at high tem­per­a­ture:

2B + N₂ = 2BN;

• re­ac­tion with oxy­gen with for­ma­tion of ni­tro­gen (II) ox­ide:

N₂ + O₂ = 2NO (takes place with heat­ing);

• re­ac­tion with hy­dro­gen with heat­ing (500 de­grees ᵒC or 932 ᵒF), high pres­sure (350 at­mos­pheres) and in the pres­ence of a cat­a­lyst (for ex­am­ple Fe):

N₂ + 3H₂ = 2NH₃;

• re­ac­tion with sodi­um car­bon­ate and re­ac­tion with coal with heat­ing:

2Na₂­CO₃ + 8C + 2N₂ = 4NaCN + 6CO;

• re­ac­tion with flu­o­rine in elec­tric dis­charge:

N₂ + 3F₂ = 2NF₃;

• re­ac­tion with cal­ci­um car­bide at a tem­per­a­ture of 1000 ᵒC (1832 ᵒF):

CaC₂ + N₂ = CaC­N₂ + C;

• re­ac­tion with hy­dro­gen with heat­ing (from 500 ᵒC or 932 ᵒF and high­er de­pend­ing on the de­mands for re­ac­tion speed and out­put), high pres­sure (around 350 at­mos­pheres) and in the pres­ence of a cat­a­lyst (for ex­am­ple, Fe or FeO):

N₂ + 3H₂ = 2NH₃.

Ni­tro­gen does not re­act di­rect­ly with sul­fur or halo­gens. The gas also does not re­act with acids, al­ka­lis or wa­ter.

Here you can find ex­cit­ing ex­per­i­ments with ni­tro­gen.

Ni­tro­gen in the ox­i­da­tion states +1, +2, +4

The ni­tro­gen ox­ides N₂O and NO are non-salt-form­ing. Ni­tro­gen ox­ide, in which ni­tro­gen has an ox­i­da­tion state of +1, has a sweet smell, and dis­solves well in wa­ter. It can be ob­tained by the ther­mal de­com­po­si­tion of am­mo­ni­um ni­trate:

NH₄NO₃ = N₂O + 2H₂O (it is im­por­tant to re­mem­ber that high tem­per­a­tures can cause de­com­po­si­tion of the ox­ide:

2N₂O = N₂ + O₂.

Ni­tro­gen (II) ox­ide

There are sev­er­al meth­ods for ob­tain­ing ni­tro­gen (II) ox­ide:

• Adding di­lut­ed ni­tric acid to cop­per (lab­o­ra­to­ry):

3Cu + 8H­NO₃ = 2NO + 3Cu(NO₃)₂ + 4H₂O.

• Cat­a­lyst ox­i­da­tion of am­mo­nia on a plat­inum-rhodi­um cat­a­lyst at 700 ᵒC or 1292 ᵒF (in­dus­try):

4NH₃ + 5O₂ = 4NO + 6H₂O.

• In the at­mos­phere the gas may form in light­ning dis­charges:

N₂ + O₂ = 2NO.

By its prop­er­ties it is a re­duc­er. The chem­i­cal prop­er­ties of ni­tro­gen (II) ox­ide are the fol­low­ing:

• 2NO + O₂ = 2NO₂;

• 5NO + 3KM­nO₄ + 2H₂­SO₄ = 2Mn­SO₄ + 3KNO₃ + Mn(NO₃)₂ + 2H₂O;

• 2NO + 2SO₂ = 2SO₃ + N₂;

• 2NO + 2CO = 2CO₂ + N₂ (rhodi­um cat­a­lyst and heat­ing re­quired);

• 6NO + 4KOH = N₂ + 4KNO₂ + 2H₂O (takes place in a flux).

Ni­tro­gen (IV) ox­ide

Ni­tro­gen (IV) ox­ide is a brown gas which dis­plays prop­er­ties of an acidic ox­ide. It has the abil­i­ty to dimer­ize.

This com­pound may be ob­tained by sev­er­al meth­ods:

1. Cu + 4H­NO₃ = Cu(NO₃)₂ + 2NO₂ + 2H₂O (con­cen­trat­ed hot wa­ter);

2. 2Pb(NO₃)₂ = 2PbO + 4NO₂ + O₂ (de­com­po­si­tion of dried ni­trate of a heavy met­al at a high tem­per­a­ture);

3. 2NO + O₂ = 2NO₂ (in in­dus­try).

Chem­i­cal prop­er­ties:

• 2NO₂ + H₂O = HNO₃ + HNO₂ (dis­pro­por­tion re­ac­tion – the ni­tro­gen atom is ox­i­dized and re­duced);

• 4NO₂ + 2H₂O + О₂ = 4H­NO₃;

• С + 2NO₂ = CO₂ + 2NO (com­bus­tion);

• S + 2NO₂ = SO₂ + 2NO (com­bus­tion).

Ni­tro­gen in the ox­i­da­tion state of +3

Ni­tro­gen has an ox­i­da­tion state of +3 in the ox­ide N₂O₃ (a dark blue liq­uid with acidic prop­er­ties) and ni­trous acid HNO₂. Ni­tro­gen (III) ox­ide can be ob­tained by the fol­low­ing re­ac­tions:

1. Cool­ing a mix­ture of ox­ides (II) and (IV) at a tem­per­a­ture of -36 ᵒC or -32.8 ᵒF):

NO + NO₂ = N₂O₃.

2. De­hy­dra­tion of ni­trous acid (de­hy­drat­ing agent – phos­pho­rus ox­ide P₄O₁₀):

2H­NO₂ = N₂O₃ + H₂O.

It dis­plays typ­i­cal acidic prop­er­ties:

• N₂O₃ + H₂O = 2H­NO₂;

• N₂O₃ + 2NaOH = 2NaNO₂ + H₂O;

• N₂O₃ + Na₂O = 2NaNO₂.

Ni­trous acid is a weak acid, and con­cen­trat­ed so­lu­tions have a bluish tiny. It is ob­tained by di­lu­tion of the ac­cord­ing ox­ide:

2H­NO₂ = N₂O₃ + H₂O or in a mix­ture with ni­tric acid di­lut­ed with ni­tro­gen (IV) ox­ide:

2NO₂ + H₂O = HNO₃ + HNO₂.

It dis­plays typ­i­cal acidic prop­er­ties – it re­acts with al­ka­lis and base ox­ides with for­ma­tion of salts. It can be an ox­i­diz­er and a re­duc­er:

• 2H­NO₂ + 2HI = I₂ + 2NO + 2H₂O (ox­i­diz­er);

• NO₂ + Cl₂ + H₂O = HNO₃ + HCl (re­duc­er).

It de­com­pos­es when heat­ed. Salts of ni­trous acid – for ex­am­ple ni­trites of al­ka­line met­als are high­ly sol­u­ble col­or­less (yel­low­ish) crys­talline sub­stances.

Ni­tro­gen in an ox­i­da­tion state of +5

N₂O₅ is a sol­id un­sta­ble sub­stance with acidic prop­er­ties. It can be ob­tained by the re­ac­tions:

1. Pass­ing the ac­cord­ing acid through a col­umn with phos­pho­rus (V) ox­ide:

4H­NO₃ + P₄O₁₀ = 2N₂O₅ + 4H­PO₃ (cool­ing to -10 ᵒC or 14 ᵒF is re­quired).

2. Ozone re­act­ing with ni­tro­gen (IV) ox­ide:

2NO₂ + O₃ = N₂O₅ + O₂.

Chem­i­cal prop­er­ties:

1. De­com­po­si­tion into oxy­gen and ni­tro­gen (4) ox­ide:

2N₂O₅ = 4NO₂ + O₂;

2. Dis­solv­ing in wa­ter:

N₂O₅ + H₂O = 2H­NO₃;

3. Re­ac­tions with bases and base ox­ides:

N₂O₅ + 2NaOH = 2NaNO₃ + H₂O; N₂O₅ + Na₂O = 2NaNO₃.

Ni­trous acid is a strong ox­i­diz­er (by its phys­i­cal prop­er­ties it is a col­or­less liq­uid with no smell). It can be ob­tained in the lab­o­ra­to­ry as fol­lows:

KNO₃ + H₂­SO₄ = KHSO₄ + HNO₃ (con­cen­trat­ed sul­fu­ric acid is tak­en).

In in­dus­try a three-stage process is used:

1. Ox­i­da­tion of am­mo­nia (plat­inum cat­a­lyst and heat­ing to 500 ᵒC or 932 ᵒF re­quired):

4NH₃ + 5O₂ = 4NO + 6H₂O.

2. *Ox­i­da­tion of ob­tained ox­ide in air to NO₂:

2NO + O₂ = 2NO₂.

3. Dis­so­lu­tion of NO₂ in wa­ter in an ex­cess of oxy­gen:

4NO₂ + О₂ + 2H₂O = 4H­NO₃.

Main chem­i­cal prop­er­ties (be­sides those typ­i­cal for all acids):

1. 4H­NO₃ = 4NO₂ + 2H₂O + O₂ (de­com­po­si­tion of con­cen­trat­ed acid in light);

2. S + 4H­NO₃(conc.) = SO₂ + 4NO₂ + 2H₂O (re­ac­tion with non-met­als).

Con­cen­trat­ed and di­lut­ed ni­tric acid re­act with met­als with­out re­lease of hy­dro­gen:

• 4H­NO₃ + Cu = Cu(NO₃)₂ + 2NO₂ + 2H₂O (con­cen­trat­ed acid);

• 8H­NO₃ + 3Cu = 3Cu(NO₃)₂ + 2NO + 4H₂O (di­lut­ed acid);

• 10H­NO₃ + 8Na = 8NaNO₃ + N₂O + 5H₂O (con­cen­trat­ed acid);

• 10H­NO₃ + 8Na = 8NaNO₃ + NH₄NO₃ + 3H₂O (di­lut­ed acid).

Con­cen­trat­ed ni­tric acid pas­si­vates iron, chromi­um, alu­minum, gold, plat­inum and irid­i­um. Many ni­trates (salts of ni­tric acid) are sol­u­ble in wa­ter.

Ni­tro­gen com­pounds are used in medicine (liq­uid am­mo­nia, am­mo­nia spir­it), agri­cul­ture (fer­til­iz­ers) and in in­dus­try for the syn­the­sis of sev­er­al or­gan­ic com­pounds.