Nitrous oxide

Nitrous oxide

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Nitrous oxide : It is also called Laughing Gas.

Method of preparation:

1) By the reaction  of zinc or iron on cold and dilute HNO₃ : 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 25O^oC gives nitrous oxide.

source : etc.usf.edu

(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.

Purification:

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 O_2(mixture)  is used as anesthetic agent in surgical  operation.

Structure of Nitrous oxide :

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