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| Nitrogen dioxide | |
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| Identifiers | |
| CAS number | [10102-44-0] |
| Properties | |
| Molecular formula | NO2 |
| Molar mass | 46.0055 |
| Appearance | brown gas |
| Density | 1443 kg/m³, liquid 3.4 kg/m³, gas at 294.25 K |
| Melting point |
-11.2°C (261.95 K) |
| Boiling point |
21.1°C (293.25 K) |
| Hazards | |
| EU classification | Highly toxic (T+) |
| NFPA 704 |
 0
3
0
|
| R-phrases | R26, R34 |
| S-phrases | (S1/2), S9, S26, S28,S36/37/39, S45 |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox references |
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Nitrogen dioxide is the chemical compound with the formula NO2. It is one of the several nitrogen oxides. This reddish-brown toxic gas has a characteristic sharp, biting odor. NO2 is one of the most prominent air pollutants.
Contents |
Preparation and reactions
Nitrogen dioxide (NO2) arises from the aerobic oxidation of nitric oxide:
- 2 NO + O2 → 2 NO2
In the laboratory, NO2 can be prepared by treating of nitric acid (HNO3) with copper metal. The reaction is the following:[1]
- 4 HNO3 + Cu → Cu(NO3)2 + 2 NO2 + 2 H2O
NO2 exists in equilibrium with its dimer, N2O4, which is colourless and diamagnetic.
Safety and pollution considerations
Nitrogen dioxide is toxic by inhalation but the material is so acrid that accidental poisoning is easily avoided. For example, fuming nitric acid is often contaminated with NO2. Symptoms of poisoning (lung edema) tend to appear several hours after one has inhaled a low but potentially fatal dose. Also, low concentrations (4 ppm) will anesthetize the nose, thus creating a potential for overexposure.
Long-term exposure to NO2 at concentrations above 40–100 µg/m³ causes adverse health effects[2].
Nitrogen dioxide is formed in most combustion processes using air as the oxidant. At elevated temperatures nitrogen combines with oxygen to form nitrogen dioxide:
- 2O2 + N2 → 2 NO2
The most important sources of NO2 are internal combustion engines [3], thermal power stations and, to a lesser extent, pulp mills. Atmospheric nuclear tests are also a source of nitrogen dioxide, which is responsible for the reddish colour of mushroom clouds[4] The excess air required for complete combustion of fuels in these processes introduces nitrogen into the combustion reactions at high temperatures and produces nitrous oxides (NOx). Limiting NOx production demands the precise control of the amount of air used in combustion.
The map shown below, depicting results of satellite measurements over Europe, illustrates nitrogen dioxide as large scale pollutant, with rural background ground level concentrations in some areas around 30 µg/m³, not far below unhealthful levels. Nitrogen dioxide plays a role in atmospheric chemistry, including the formation of tropospheric ozone. A recent study by researchers at the University of California, San Diego, suggests a link between NO2 levels and Sudden Infant Death Syndrome. [5]
See also
- Nitryl
- Nitrous oxide or N2O, "laughing gas", a linear molecule, isoelectronic with CO2 but with a nonsymmetric arrangement of atoms (NNO)
- Nitric oxide or NO, a problematic pollutant that is short lived because it converts to NO2 in the presence of free oxygen.
- NOx = all of the above in unspecified proportions but tending toward NO2.
More esoteric nitrogen oxides include N2O5 and the blue species N2O3.
Oxidized (cationic) and reduced (anionic) derivatives of many of these oxides exist: nitrite (NO2−), nitrate (NO3−), nitronium or NO2+, and nitrosonium or NO+. NO2 is intermediate between nitrite and nitronium:
-
- NO2+ + e− → NO2
- NO2 + e− → NO2−
References
- ^ Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.
- ^ "Health Aspects of Air Pollution with Particulate Matter,Ozone and Nitrogen Dioxide". Retrieved on 2008-02-25.
- ^ Son, Busoon; Wonho Yang, Patrick Breysse, Taewoong Chung and Youngshin Lee (March 2004). "Estimation of occupational and nonoccupational nitrogen dioxide exposure for Korean taxi drivers using a microenvironmental model". Environmental Research 94 (3): 291–296. doi:. Retrieved on 2008-02-25.
- ^ "Air emissions". Botnia. Retrieved on 2008-02-25.
- ^ "Sids Linked to Nitrogen Dioxide Pollution". Retrieved on 2008-02-25.
External links
- International Chemical Safety Card 0930
- National Pollutant Inventory - Oxides of nitrogen fact sheet
- NIOSH Pocket Guide to Chemical Hazards
- WHO-Europe reports: Health Aspects of Air Pollution (2003) (PDF) and "Answer to follow-up questions from CAFE (2004) (PDF)
- Nitrogen Dioxide Air Pollution
- Nitrogen dioxide pollution in the world (image)
- Computational Chemistry Wiki
Wikipedia content modification information:
- This page was last modified on 3 October 2008, at 11:54.
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