Nitrogen Dioxide

Descriptionnitrogen dioxide is a reddish-brown gas (or yellow liquid) with a strong, acrid odor. Nitrogen dioxide readily dimerizes to produce N2O4.nitrogen dioxide are nonfl ammable, toxic gases.The federal government has established air quality standards for nitrogen dioxide at 0.053 partsper million (ppm), which equals 100μg (micrograms) per cubic meter.Nitrogen dioxide is highly soluble in water and forms nitric acid (HNO3), and nitric oxide is slightly soluble and forms nitrous acid (HNO2).Nitrogen dioxide is a strong oxidizing agent and causes corrosion.Nitrogen dioxide is used as an oxidizing agent, a catalyst in oxidation reactions, an inhibitor, as a nitrating agent for organic reactions, as a flour bleaching agent, and in increasing the wet strength of paper.

OccurrenceNitrogen dioxide is an intermediate in producing nitric acid. It also is used in the lead chamber process for making sulfuric acid. It is used as a nitrating and oxidizing agent, in rocket fuels, in the manufacture of hemostatic cotton and other oxidized cellulose compounds, and in bleaching flour. Nitrogen dioxide occurs in trace concentrations in the atmosphere due to oxidation of nitric oxide in air. It also is found in exhaust gases of internal combustion engines, in industrial waste gases from plants using nitric acid, and in cigarette smoke. Brown color of smog in many industrial urban areas is attributed to nitrogen dioxide.

Historynitrogen dioxide was prepared in 1772 by Joseph Priestley (1733–1804) and described in his volumes Experiments and Observations of Different Kinds of Air published between 1774 and 1786. Priestley called nitric oxide nitrous air, nitrogen dioxide nitrous acid vapor, and nitrous oxide phlogisticated nitrous air, but also referred to the dioxide. Priestley prepared nitric oxide by reacting nitric acid with a metal such as copper: 3Cu(s) + 8HNO3(aq) → 2NO(g) + 3Cu(NO3)2(aq) + 4H2O(l).

UsesNitrogen dioxide is produced by the reactionof nitric acid with metals or other reducingagents; decomposition of nitrates; when airis heated to high temperatures; and duringfire. It occurs in the exhausts of internalcombustion engines and in cigarette smoke.It is used as an intermediate in the productionof nitric and sulfuric acids, in rocket fuels,as a nitrating and oxidizing agent, and inbleaching flour.

UsesNitrogen dioxide is an intermediate in producing nitric acid. It also is used in the lead chamber process for making sulfuric acid. It is used as a nitrating and oxidizing agent, in rocket fuels, in the manufacture of hemostatic cotton and other oxidized cellulose compounds, and in bleaching flour. Nitrogen dioxide occurs in trace concentrations in the atmosphere due to oxidation of nitric oxide in air. It also is found in exhaust gases of internal combustion engines, in industrial waste gases from plants using nitric acid, and in cigarette smoke. Brown color of smog in many industrial urban areas is attributed to nitrogen dioxide.

UsesNitrogen dioxide has been used as a catalyst in certain oxidation reactions, as an inhibitor to prevent polymerization of acrylates during distillation, as a nitrating agent for organic compounds, as an oxidizing agent, and as an oxidizer for rocket fuel. It is also used as a flour bleaching agent in the manufacture of liquid explosives and for increasing the wet strength of paper.

General DescriptionA reddish brown gas or yellowish-brown liquid when cooled or compressed. Shipped as a liquefied gas under own vapor pressure. Vapors are heavier than air. Toxic by inhalation (vapor) and skin absorption. Noncombustible, but accelerates the burning of combustible materials. Cylinders and ton containers may not be equipped with a safety relief device.

PreparationNitrogen dioxide may be prepared by several methods. It is produced when an electric discharge is passed through air. It is made commercially from nitric oxide and air. Nitric oxide made by various processes (See Nitric Oxide) rapidly oxidizes to nitrogen dioxide. It is formed by decomposing nitric acid or by oxidizing ammonia with air: HNO3 → NO2 + H2O 4NH3 + 7O2 → 4NO2 + 6H2O Also, nitrogen dioxide can be made by heating copper with nitric acid. In the laboratory, nitrogen dioxide is formed by heating lead nitrate or nitrate of another heavy metal: 2Pb(NO3)2 → 2PbO + 4NO2 + O2 Gaseous mixture of nitrogen dioxide and oxygen is passed through a U-tube placed in a freezing mixture. Nitrogen dioxide condenses and is collected as liquid.

DefinitionA brown gas produced by the dissociation of dinitrogen tetroxide (with which it is in equilibrium), the dissociation being complete at 140°C. Further heating causes dissociation to colorless nitrogen monoxide and oxygen: 2NO2(g) = 2NO(g) + O2(g) Nitrogen dioxide can also be made by the action of heat on metal nitrates (not the nitrates of the alkali metals or some of the alkaline-earth metals).