Oxides of nitrogen

Oxides of nitrogen range from N2O (oxidation state of nitrogen +1) through NO, N2O3, NO2, N2O4, N2O5 in which the oxidation state of nitrogen is +5

1. NO2– Nitrogen dioxide:

 NO2 is an intermediate in the industrial synthesis of nitric acid.

 This reddish – brown toxic gas has a characteristic sharp, biting odor and is a prominent air pollutant. It absorbs light and leads to the yellow-brown haze sometimes seen hanging over cities.

 It is one of the important components of smog.

 Nitrogen dioxide is a paramagnetic, bent molecule.

 Nitrogen dioxide typically arises via the oxidation of nitric oxide by oxygen in air:

2 NO + O2 → 2 NO2

 In the laboratory, NO2 can be prepared in a two-step procedure where dehydration of nitric acid produces dinitrogen pentoxide, which subsequently undergoes thermal decomposition:

2HNO3 → N2O+ H2O2

2N2O5 → 4 NO2 + O 2

 The thermal decomposition of some metal nitrates also affords NO2:

2 Pb (NO3)2 → 2 PbO + 4 NO2 + O2

 Alternatively, reduction of concentrated nitric acid by metal (such as copper).

4 HNO3 + Cu → Cu (NO3)2 + 2 NO2 +2 H2O

 Or finally by adding concentrated nitric acid over tin; hydrated tin dioxide is produced as byproduct.

4HNO3 + Sn → H2O + H2SnO3 + 4 NO2

 NO2 exists in equilibrium with the colourless gas dinitrogen tetroxide (N2O4):

2 NO2 ⇌ N2O4

 As suggested by the weakness of the N–O bond, NO2 is a good oxidizer. Consequently, it combusts, sometimes explosively, with many compounds, such as hydrocarbons.

Nitrogen dioxide

2. N2O – Nitrous oxide:

 Nitrous oxide is commonly known as laughing gas.

 At room temperature, it is a colourless, non-flammable gas, with a slightly sweet odour and taste.

 It is used in surgery and dentistry for its anaesthetic and analgesic effects.

 It is known as “laughing gas” due to the euphoric effects of inhaling it.

 It is also used as an oxidizer in the launching of rockets and in motor racing to increase the power output of engines. At elevated temperatures, nitrous oxide is a powerful oxidizer similar to molecular oxygen.

N ≡ N⁺ – O⁻ ↔ ⁻N = N⁺ = O

3. NO – Nitric oxide:

 Nitric oxide is also known as nitrogen monoxide.

 It is a free radical and is an important intermediate in the chemical industry.

 Nitric oxide is a by-product of combustion of substances as in automobile engines, fossil fuel power plants, and is produced naturally during the electrical discharges of lightning in thunderstorms.

 Nitric oxide (NO) has no colour, odour, or taste and is non-toxic. In the air it is rapidly oxidized to nitrogen dioxide.

Nitric oxide