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 → N₂O₅ + 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.

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.