Nitric acid

• Dioxidohydroxidostickstoff
• Aquafortis
• Hydrogen nitrate

Partly in pure form colorless liquid, by light or heat decomposition to nitrogen oxides under yellow to red coloration

Liquid

1.51 g · ml -1 ( 20 ° C)

-42 ° C

86 ° C.

56 hPa ( 20 ° C)

-1.37

Miscible with water in all proportions, violent reaction with ethanol

Risk

5.2 mg · m-3

430 mg • kg -1 ( LDLO, man, oral)

Template: Infobox chemical / molecular formula search is not possible

Nitric acid (named after the nomenclature of the IUPAC hydrogen nitrate) is the best known and most stable oxygen acid of nitrogen. The name is derived from the saltpetre, from which it can be obtained by addition of a stronger acid ( sulfuric acid).

Nitric acid is in aqueous solution remains largely dissociated. As a strong inorganic acid it is one of the mineral acids. Its salts and esters are called nitrates. The salts are characterized also by the common name " saltpeter ", eg: Chile saltpetre ( potassium ) saltpetre, nitrate, calcium nitrate or Mauersalpeter, Barytsalpeter etc.

The pure acid is colorless and has a sharp pungent odor. It is used inter alia for the production of fertilizers, dyes, and explosives.

History

In the De Veritatis inventione from the 12th century it is mentioned that in the 9th century Arab alchemist donor crude nitric acid ( "Aqua dissolutiva " ) by dry heating saltpetre (Latin sal Petrae = rock salt, KNO3 ), Cyprischem Vitriol ( CuSO4 · 5 H2O) and alum ( KAl (SO4) 2:12 H2O) should have won. In the 13th century, Albertus Magnus is said to have used the nitric acid to separate gold and silver ( " aqua fortis "). However, many writings Albertus Magnus were only attributed to give them more weight, probably via the use of nitric acid. Later saltpeter with vitriol was ( FeSO4 · 7 H2O) heated to afford higher yields at lower temperature.

JR Glauber won the mid-17th century pure spiritus nitri by reaction and distillation of nitric acid with sulfuric acid, a modern common laboratory method for the preparation of nitric acid, which was called in the Middle Ages also aqua fortis or aqua valens and in the English language strong water. As components of nitric AL Lavoisier recognized mid-18th century, the chemical elements nitrogen and oxygen. The exact composition was determined by Henry Cavendish, which also includes the synthesis of the nitrogen of the air was achieved by electrical discharge.

A rational production did not begin until the early 19th century, when cheap sulfuric acid and Chilean nitrate were available in sufficient quantities. The " combustion air " in an electric arc has been developed into a large-scale processes ( Birkeland Eyde ), which, however, was competitive with cheap electricity in countries. The catalytic oxidation of ammonia to platinum was discovered by Kuhlmann CF (1838). Until the invention of the synthesis of ammonia by Haber and Bosch ammonia but remained too expensive compared to Chile saltpetre. At the beginning of the 20th century Wilhelm Ostwald developed the production of nitric acid from ammonia to industrial maturity. The cheap ammonia oxidation has displaced all other industrial processes today.

Production

Nitric acid is produced industrially since 1908 by the Ostwald process. It involves the catalytic oxidation of ammonia. The ammonia - air mixture (1/ 1000 seconds contact time ) conducted quickly by hot platinum-rhodium networks ( catalyst). At 800 ° C produced nitric oxide, which reacts upon cooling with excess oxygen to form nitrogen dioxide and then in scrubbers with water to about 60% nitric acid. The 60 % nitric acid can be concentrated by distillation to 68 %, which (122 ° C ) corresponds to the maximum boiling point azeotrope with. Higher concentrations can be obtained by rectification ( drainage) with sulfuric acid ( H2SO4) or with aqueous magnesium nitrate solution ( Mg ( NO3 ) 2) or by treatment of dinitrogen tetroxide ( N2O4 ) with the stoichiometrically required oxygen (or air ) and water reach.

Nitric acid on a laboratory scale can be represented by reacting concentrated sulfuric acid with nitrates. Nitric acid was obtained by this method by using sodium nitrate ( Chile saltpetre ) before 1908.

Often occurring impurities in the acid with halogens or hydrogen halides can be eliminated by addition of silver nitrate and subsequent distillation. Anhydrous nitric acid is obtained from a highly concentrated by distillation acid starting by passing an inert gas or by distillation over phosphorus pentoxide or oleum.

Properties

Nitric acid is colorless in the pure state. However Concentrated nitric acid decomposes easily (especially when exposed to light ) and, on account of her in dissolved nitrogen dioxide (NO2 ) is often a yellowish or reddish hue. Of pure nitric acid, the nitrogen containing free is called fuming nitric acid. It contains over 90 % HNO3, is highly oxidizing and can ignite some flammable substances; therefore applies from 70% nitric acid as oxidizing. Nitric acid, which is colored yellow by dissolved nitrogen dioxide can be discolored by a small amount of urea urea nitrate or better.

Nitric acid dissolves most metals. Exceptions are the precious metals gold, platinum and iridium. Also, aluminum, titanium, zirconium, hafnium, niobium, tantalum and tungsten resist dissolution by nitric acid by passivation. It forms on the metal an adherent, impervious oxide layer. Thus, since one could separate gold and silver, it was formerly called aqua fortis. Mixed with hydrochloric acid ( aqua regia ) or selenium acid can dissolve gold and platinum. Next are aluminum and iron due to passivation resistant to cold, chrome to hot nitric acid.

Nitric colored protein containing aromatic amino acids such as L-phenylalanine or L-tyrosine, under yellow nitration of the benzene ring. Xanthoproteic this reaction can be used for the detection of aromatic amino acids and proteins.

Use

Nitric acid is one of the main raw materials in the chemical industry. It is used:

• In the form of their salts ( nitrates) as a fertilizer and for explosives,
• As a salt of silver nitrate in the photographic industry,
• As aqua fortis for separation ( Quartation ) of gold and silver ( silver is dissolved )
• In mixtures with hydrochloric acid as aqua regia to dissolve gold and gilding and for the detection of gold
• In the ratio 3 parts hydrochloric acid to one part nitric acid for digestion in analytical chemistry according to DIN EN 13 346 of soils and sewage sludge
• For pickling and burning of metals ( graphical and electrical engineering),
• For the nitration of organic compounds in the manufacture of dyes, medicines, explosives and disinfectants,
• In the form of their esters for the production of explosives ( blasting oil ), celluloid, nitro and Zaponlacke,
• For modifying fats (water ) for the purpose of purification,
• For polishing metals.
• As a component of rocket fuels (See WFNA and fuming )

Mixtures with sulfuric acid and nitrating acid are called used for the nitration of organic compounds.

It was until the late 1980s, used in rocket technology as the oxidizer (eg in the Agena upper stage ).

Proof

Nitric acid can be detected by nitrate detection by the ring sample and reagent Lunges. These detection methods are also referred to as a traditional process.

Safety

Nitric acid acts on the skin, respiratory tract and mucous membrane irritant and strong is to destroy living tissue in a position ( burns ). In high concentrations it is a strong oxidizing agent and oxidizing.