chemical element nitrogen with a serial number 7 is a 5 group of the periodic table.This diatomic gas under normal conditions is quite inert.In the Earth's atmosphere, it accounts for three quarters.The element has the following oxidation states of -3, -1, 0, 1, 2, 3, 4, and 5. It is part of many compounds.One of them is a reddish-brown toxic gas (characterized by the ability to irritate the respiratory tract, causing pulmonary edema at high concentrations), which has a characteristic sharp, pungent odor - is nitrogen dioxide.The formula is NO2.Molar mass 46.01 g / mol.Density 2.62 g / l.Boiling point 21 ° C.When dissolved in water, react with it.The refractive index of 1.449 (at 20 ° C).
Nitrogen dioxide plays an important role in the chemistry of the atmosphere, including the formation of tropospheric ozone.At the same time it is a major air pollutant, and intermediate in the industrial synthesis of nitric acid, which produces millions of tons each year.This is one of several nitrogen oxides (binary inorganic compounds of nitrogen and oxygen) with oxidation:
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I - nitrous oxide, N2O;
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II - nitrogen monoxide NO;
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III - dinitrogen trioxide, N2O3;
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IV - nitrogen dioxide NO2 and dinitrogen tetroxide N2O4;
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V - dinitrogen pentoxide N2O5;
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trinitramid N (NO2) 3.
Nitrogen dioxide is easily liquefied.It is heavier than air.Under normal conditions NO2 mixed (approximately 1: 1) with a colorless material (its dimer) N2O4.Chemistry NO2 well studied.
in contact with water is hydrolyzed, resulting in formation of two acid (nitrous and nitric): 2NO2 + H2O → HNO2 + HNO3.
In reactions with alkali salts are formed as these two acids: 2NaOH + 2NO2 → NaNO2 + NaNO3 + H2O.
He is a strong oxidant capable of oxidizing SO2 to SO3.This method of its properties based nitrous sulfuric acid.NO2 Among many substances, including organic compounds, sulfur, carbon and phosphorus, burn.
Nitrogen dioxide is usually formed by the oxidation of nitric oxide by atmospheric oxygen: O2 + 2NO → 2NO2
Laboratory NO2 produced in two stages: dehydration of nitric acid to pentoxide dinitrogen, which is then decomposed thermally:
2HNO3 → N2O5 +H2O,
2N2O5 → 4NO2 + O2.
a result of thermal decomposition of nitrates of some metals can also be obtained NO2:
2Pb (NO3) 2 → 4NO2 + 2PbO + O2.
The oxide can be formed by reaction of nitric acid (concentrated) from metals (e.g., copper):
4HNO3 → 2NO2 + Cu + Cu (NO3) 2 + 2H2O.
When exposed to nitric acid (concentrated) tin besides nitrogen dioxide, tin acid formed as a byproduct:
4HNO3 → Sn + H2O + 4NO2 + H2SnO3.
Some sources oxide N2O4 (IV) was referred to as nitrogen tetroxide.But this is a misnomer, as the substance is dinitrogen tetroxide.NO2 exists in equilibrium with a colorless gas N2O4: 2NO2↔N2O4.
Since this balance is exothermic, it is shifted towards NO2 at higher temperatures and at lower - in the direction N2O4.Diemer goes into the solid state at a temperature of minus 11.2 ° C.At a temperature of 150 degrees can be expanded: N2O4 → 2NO2, then 2NO2 → 2NO + O2.
Nitric acid slowly releases NO2, which gives the characteristic yellow color of most of the samples of this acid:
4HNO3 → 4NO2 + 2H2O + O2.
Nitrogen dioxide is easy to detect by smell even at low concentrations, inhalation of vapors should be avoided.One potential source of NO2 is fuming nitric acid, which allocates NO2 at temperatures above 0 degrees.Symptoms of poisoning (pulmonary edema), usually appear after inhalation of potentially lethal doses of a few hours.There is some evidence that long-term exposure to NO2 at concentrations above 40-100 mg / m³ can reduce lung function and increase the risk of respiratory symptoms.In studies of some scientists established a connection between the concentration of NO2 and sudden infant death syndrome.
Nitrogen dioxide formed in most combustion processes where air is used as the oxidant.
At elevated temperatures, nitrogen combines with oxygen to form nitric oxide: O2 + N2 → 2NO, then NO is oxidized in air to form dioxide O2 + 2NO → 2NO2:
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Under normal atmospheric concentration is a very slow process.
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The most likely sources of NO2 are combustion engines, thermal power stations and, to a lesser extent, pulp mills.
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gas heaters and stoves are also sources of this oxide.The required combustion air excess introduces nitrogen, which is converted at elevated temperatures into oxides of nitrogen.
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in household kerosene heaters and gas heaters are also sources of NO2.
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Nitrogen dioxide is produced when atmospheric nuclear tests (reddish mushroom cloud).
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In some rural areas it can reach the surface concentrations of 30 mg / m³.
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NO2 is also naturally produced by thunder, rain.
