Nitrogen Family : Nitrogen and its compounds

Nitrogen and its compounds

N2 was discovered by Daniel Rutherford. It is the first member of group 15 in the periodic table.

(1)     Occurrence : N2, occurs both in the free state as well as in the combined state.  N2 occurs in atmosphere to the extent of 78% by volume in free state. N2 is present in many compounds such as potassium nitrate (nitre). Sodium nitrate (Chile salt peter) and many ammonium compounds. N2 is an important constituent of proteins in plants and animals in combined state.

(2)     Preparation : It is prepared  by the following methods,

(i)      Laboratory method : In the laboratory N2 is prepared by heating an aqueous solution containing an equivalent amounts of NH4Cl and NaNO2.

          NH4Cl (aq.) + NaNO2 (aq.) \underrightarrow { \quad Heat\quad } N2(g) + 2H2O(l) + NaCl

(ii)     Commercial preparation : Commercially N2 is prepared by the fractional distillation of liquid air.

(3)     Physical properties : N2 is a colourless, odourless and tasteless gas. It is a non-toxic gas. It’s vapour denstiy is 14. It has very low solubility in water.

(4)     Chemical properties

(i)      N2 is neutral towards litmus. It is chemically unreactive at ordinary temp. It is neither combustible nor it supports combustion.

(ii)     The N – N bond in N2 molecule is a triple bond (N ≡ N) with a bond distance of 109.8 pm and bond dissociation energy of 946 kJ mol-1

(iii)    Combination with compounds : N2 combines with certain compounds on strong heating . eg

\underset { Calsium\quad Carbide }{ Ca{ C }_{ 2 } } +\quad { N }_{ 2 }\quad \underrightarrow { \quad 1300\quad K\quad } \quad \underset { Calcium\quad cyanamide }{ Ca{ CN }_{ 2 }\quad +\quad C }

\underset { Aluminium\quad \\ \quad \quad oxide }{ Al_{ 2 }{ O }_{ 3 } } +\quad { N }_{ 2 }\quad +\quad 3C\quad \underrightarrow { \quad 2100\quad K\quad } \quad \underset { Al\quad nitride }{ 2AlN\quad +\quad 3\quad CO }     

Both these compounds are hydrolysed on boiling with water to give ammonia.

          CaCN2 + 3H2O → CaCO3 + 2NH3 ;

          AlN + 3H2O → Al (OH)3 + NH3

Therefore, calcium cyanamide is used as a fetilizer under the name nitrolim (CaCN2 + C)

(5)     Uses of nitrogen : N2 is mainly used in the manufacture of compounds like NH3, HNO3, CaCN2 etc.