Nitrogen is a very important part of our atmosphere. It forms 78% of our atmosphere by volume and 75% by mass.
Preparation : We have two types of productions of Nitrogen:
Commercial production : The commercial production of Nitrogen is done by the liquifaction and fractional distillation of air.
Lab production : In lab Nitrogen can be produced by several methods-
I. When aqueous solution of ammonium chloride is treated with sodium nitrite.
NH4Cl(aq)+NaNO2(aq)→ N2(g) + 2H2O(l) + NaCl(aq)
II. Dinitrogen can also be obtained by the thermal decomposition of ammonium dicromate.
(NH4)2Cr2O7 →N2(g) + 2H2O(l) + Cr2O3
III. Thermal decomposition of sodium or barium azide also gives dinitrogen. Nitrogen obtained by this method is very pure.
Ba(N3)2 → Ba + 3N2
Ammonia was detected by Priestley in 1774. It is generally formed by the bacterial decomposition of nitrogenous matter found in plants and animals. We can find it in a very less amount in air and soil.
Commercial production: Ammonia is produced by Haber’s process commercially. In this process we prepare a setup with following optimum conditions:
1. Pressure :200 × 105 Pa or 200 atm(Approx), 2. Temperature : About 700 K & 3. Catalyst : Iron oxide with small amount of K2O & Al2O3.
Under these conditions ammonia is produced by the reaction : N2(g) + 3H2(g) → 2NH3(g)
The catalyst is used to increase the production rate of NH3.
III. Oxides of Nitrogen
Nitrogen reacts with oxygen to form different oxides with different oxidation state
1. N2O -Dinitrogen Oxide or Nitrous Oxide or Laughing Gas:
Oxidation state of Nitrogen: 1
Preparation: It can be produced by heating ammonium nitrate.
NH4NO3 N2O + 2H2O
Properties : 1. Nitrous oxide is a colourless gas.
2. It is a has with sweet taste and pleasant odour.
3. It can create laughter when inhaling in a sufficient amount due to which it is called laughing gas.
4. It is soluble in cold water but not in hot water.
5. Nitrous oxide is heavier than air.
Uses : 1. As propellant, 2. As anaesthetic in minor surgical operations with oxygen
II. HNO3-Nitric Acid
Commercial Preparation(Ostwald Process):
The mixture of ammonia and air when passed over platinum gauze catalyst at 7500C-9000C, then ammonia is oxidised to nitric acid.
4NH3+5O2 – 4NO + 6H2O
By oxidising, the nitric oxide is converted to nitrogen dioxide.
2NO + O2 – 2 NO2
When nitrogen dioxide is cooled and absorbed in water, nitric acid is obtained.
3NO2 + H2O – 2HNO3 + NO
Lab Preparation: In the laboratory, nitric acid is formed by heating the mixture of KNO3 or NaNO3 and concentrated H2SO4 in a glass retort.
KNO3 + H2SO4 – KHSO4 + HNO3
NaNO3 + H2SO4 – NaHSO4 + HNO3
Elements in 15th group are known as ‘The Nitrogen Family’. The family includes the following elements:
Occcurence : Nitrogen – Nitrogen is found in the molecular form in the atmosphere. It comprises 75% by mass and 78% by volume of the atmosphere. It is also found in Earth’s crust in the form of Chile Saltpetre(Sodium Nitrate : NaNO3) and Indian Saltpetre(Potassium Nitrate-KNO3). In the form of protein, Nitrogen is also available in plants and animals.
Phosphorus : Minerals of the apatite family are main source of phosphorus as flourapatite : Ca9(PO4)6.CaX2 where X =F, Cl and Br. In the animal and plant matter nitrogen is an essential component. It is also found in bones of animals. As phosphoproteins it is available in milk and eggs.
Arsenic, Antimony & Bismuth : They are found in sulphide minerals.
Properties of 15th group elements :
◆ Atomic properties :
● Electronic configuration : The electronic configuration of the outermost shell is ns2np3. Due to half filled p orbital these elements are quite stable.
● Atomic & ionic radio :
Reactivity towards oxygen : Group 15 elements form oxides by reacting with oxygen of the form E2O3, E2O4 and E2O5 .Ex: N2O3, N2O4, P2O5, As2O5 etc.
Key Points : 1. Among oxides the acidic nature increases with increase in the oxidation state.
2. The acidic nature also increases with increase in the percentage of oxygen.
3. In the group, the acidic nature decrease with increase in atomic number due to increase in the metallic character.
E2O3 Type Oxides of
Nitrogen & Phosphorus
Arsenic & Antimony
4. The stability of oxides decreases down the group.
Reactivity towards Hydrogen : Group 15 elements react with Hydrogen to form hydrides of the form EH3. Ex : NH3 (Ammonia), PH3 (Phosphine), BiH3 (Bismuthine) etc.
Key Points : 1. The thermal stability decreases down the group because the tendency to form covalent bond decreases as the size of atoms increases which leads to increase in the metallic character.