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Nitrogen dioxide

The chemical element nitrogen with the serial number 7 is located in the 5th group of the periodic system of Mendeleyev. This diatomic gas is inert under normal conditions. In the earth's atmosphere, it accounts for three quarters. The element is characterized by the following degrees of oxidation: -3, -1, 0, 1, 2, 3, 4, 5. It is a part of many compounds. One of them is a reddish-brown poisonous gas (characterized by the ability to irritate the respiratory tract, causes pulmonary edema at high concentrations), which has a characteristic sharp, pungent smell - it is nitrogen dioxide. The formula has the form NO2. The molar mass is 46.01 g / mol. The density is 2.62 g / dm3. The boiling point is 21 ° C. When dissolved in water, it reacts with it. The refractive index is 1,449 (at 20 ° C).

Nitrogen dioxide plays an important role in atmospheric chemistry, including in the formation of tropospheric ozone. At the same time, it is a major air pollutant and intermediate in the industrial synthesis of nitric acid, millions of tons of which are produced every year. This is one of several nitrogen oxides (binary inorganic nitrogen compounds with oxygen) with degrees of oxidation:

  • I - nitrous oxide N2O;

  • II - nitrogen monoxide NO;

  • III - diazotite trioxide N2O3;

  • IV - nitrogen dioxide NO2 and dinitrogen tetroxide N2O4;

  • V - diazotite pentoxide N2O5;

  • Trinitramide N (NO2) 3.

Nitrogen dioxide easily liquefies. He is heavier than air. Under normal conditions, NO2 is mixed (about 1: 1) with a colorless substance (its dimer) N2O4. Chemistry of NO2 is well studied.

When interacting with water, it hydrolyzes, resulting in the formation of two acids (nitrogen and nitrogen): 2NO2 + H2O → HNO2 + HNO3.

In reactions with alkalis, salts of the same two acids are formed: 2NaOH + 2NO2 → NaNO2 + NaNO3 + H2O.

It is a strong oxidizer, capable of oxidizing SO2 to SO3. This method is based on the method of nitrous production of sulfuric acid. In NO2 environment, many substances, including organic compounds, sulfur, coal and phosphorus, are burning.

Nitrogen dioxide is usually formed as a result of the oxidation of nitric oxide by air oxygen: O2 + 2NO → 2NO2

In the laboratory, NO2 is obtained in two steps: dehydration of nitric acid to diazotene pentoxide, which is then decomposed by thermal means:

2HNO3 → N2O5 + H2O,

2N2O5 → 4NO2 + O2.

As a result of the thermal decomposition of nitrates of certain metals, it is also possible to obtain NO2:

2Pb (NO3) 2 → 4NO2 + 2PbO + O2.

Oxide can be formed by the interaction of nitric acid (concentrated) with metals (for example, copper):

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

Under the influence of nitric acid (concentrated) on tin, in addition to nitrogen dioxide, tin acid is formed as a by-product:

4HNO3 + Sn → H2O + H2SnO3 + 4NO2.

In some sources, the oxide of N2O4 (IV) is called only tetroxide of nitrogen. But this is an incorrect name, since the substance is a dinitrogen tetroxide. NO2 exists in equilibrium with a colorless gas N2O4: 2NO2↔N2O4.

Since this equilibrium is exothermic, it shifts toward NO2 at higher temperatures, and at lower temperatures towards N2O4. The dimer passes into a solid state at a temperature of minus 11.2 ° C. At a temperature of 150 degrees, N2O4 → 2NO2 decomposes, followed by 2NO2 → 2NO + O2.

Nitric acid slowly releases NO2, which gives a characteristic yellow color to most of the samples of this acid:

4HNO3 → 4NO2 + 2H2O + O2.

Nitrogen dioxide is easy to detect by smell even at low concentrations, it is best to avoid inhaling its vapors. One of the potential sources of NO2 is fuming nitric acid, which releases NO2 at temperatures above 0 degrees. Symptoms of poisoning (pulmonary edema) usually appear after inhaling potentially lethal doses in a few hours. There is some evidence that long-term exposure to NO2 at concentrations above 40-100 μg / m³ can reduce lung function and increase the risk of respiratory symptoms. In studies of some scientists, the relationship between the concentration of NO2 and the syndrome of sudden infant death has been established.

Nitrogen dioxide is formed in most combustion processes, where air is used as an oxidizing agent.

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:

  1. At normal atmospheric concentrations this is a very slow process.

  2. The most likely sources of NO2 are internal combustion engines, thermal power plants and, to a lesser extent, cellulose plants.

  3. Gas heaters and furnaces are also sources of this oxide. The excess air required for combustion is brought in by nitrogen, which at high temperatures is converted to nitrogen oxides.

  4. In households, kerosene heaters and gas heaters are also sources of NO2.

  5. Nitrogen dioxide is produced in atmospheric nuclear tests (the reddish color of a mushroom cloud).

  6. In some agricultural areas, its surface concentrations can reach 30 μg / m³.

  7. NO2 is also naturally produced by thunder and rain.

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