Nitrous oxide

Nitrous oxide

Nitrous oxide : It is also called Laughing Gas.

Method of preparation:

1) By the reaction  of zinc or iron on cold and dilute HNO: Nitrous oxide is formed.
4 Zn + 10 HNO3 ——–> 4 Zn(NO3)2 + N2O + 5H2O
4 Fe + 10 HNO3   ——–> 4 Fe(NO3)2 (ferrous nitrate) + N2O + 5 H2O
2) By  reduction of HNO3 with SnCl2 and HCl : Nitrous oxide is formed.
4 SnCl2 (stannous chloride) + 8 HCl + 2 HNO3 ——–>  N2O +  4 SnCl4 (stannic chloride) +  5 H2O
Laboratory method:

A mixture of ammonium sulphate and sodium nitrate on heating below 25OoC gives nitrous oxide.



source :

(NH4)2SO4 + 2 NaNO3  ——-> Na2SO4 + 2NH4NO3
NH4NO3 ——-> 2H2O + N2O
N2O may be obtained by direct heating  of  Ammonium nitrate   below 250 oC but reaction is very fast and explosion takes place.

N2O is collected over hot water because it is soluble in cold water.


Nitrous oxide  contains  impurities of Cl2, HNO3, NO (nitric oxide), NH3 and water vapour. To remove these impurities it  is passed to the solution containing NaOH, FeSO4 and concentrated H2SO4.

Sodium hydroxide removes the impurities of  chlorine & nitric acid.
Cl2 +NaOH  ——–> NaCl + NaClO +H2O
HNO3 +NaOH ——> NaNO3 + H2O

Ferrous sulphate  removes the impurity  of  nitric oxide
FeSO4 + NO ——-> FeSO4.NO (Nitroso ferrous sulphate)

Sulphuric acid  removes the impurities of  ammonia  & water vapour.
2NH3 + H2SO4 —–> (NH4)2SO4

Concentrated H2SO4 is dehydrating agent it also absorbs water vapours.

Physical properties:


  • Nitrous oxide is colorless sweet smelling gas.
  • Laughing gas is soluble in cold water but insoluble in hot water.
  • If N2O is inhaled for a long time it produces insensibility and may cause even death.
  • It is a neutral oxide and has no effect on litmus paper.

Chemical properties:

a) Decomposition: It decomposition  starts at 5200C & completely decomposed at 9000C

2N2O ——> 2N2 + O2 (at electric spark)

At high temp.

2N2O —–> 2NO + N2

b)Reaction with Sodamide:

N2O + NaNH2 (Sodamide) ——–>NaN3 (Sodium azide) + H2O

Uses :

N2O and O2(mixture)  is used as anesthetic agent in surgical  operation.

Structure of Nitrous oxide :


source :