What is the charge of HNO3

Structural formula
Surname nitric acid
other names

Dioxidohydroxido nitrogen, septic fluid, hydrogen nitrate

Molecular formula ENT3
CAS number 7697-37-2[1]
Brief description colorless (pure), light yellow to reddish liquid (depending on the dissolved nitrogen oxide)
Molar mass 63.01 g mol−1[1]
Physical state liquid
density 1.52 g / ml (20 ° C)[1]
Melting point −42 ° C[1]
boiling point 86 ° C[1]
Vapor pressure

56 hPa[1] (20 ° C)

pKa value



Miscible with water in all proportions, violent reaction with ethanol[1]

safety instructions

5.2 mg m−3[2]


430 mg / kg[1] (Human)

As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions.

nitric acid (according to the IUPAC nomenclatureHydrogen nitrate called) is the best known and most stable oxygen acid of nitrogen. The name is derived from saltpeter, from which it can be obtained by adding a stronger acid (hydrochloric acid, sulfuric acid).

Nitric acid is largely dissociated in aqueous solution. As a strong inorganic acid, it is one of the mineral acids. Their salts and esters are called nitrates. The salts are also identified with the common name "-salpeter", e.g. E.g .: Chile nitrate, (potash) saltpeter, ammonium nitrate, lime nitrate, barite nitrate, wall nitrate, etc.


In scripture De inventione veritatis From the 12th century it is mentioned that as early as the 9th century the Arab alchemist giver raw nitric acid ("aqua dissolutiva") by dry heating of saltpeter (lat. sal petrae = Rock salt; KNO3), Cypric vitriol (CuSO4· 5H2O) and alum (KAl (SO4)2· 12H2O) is said to have won. In the 13th century Albertus Magnus used nitric acid to separate gold and silver ("separating water"). Many scripts were erroneously ascribed to Albertus Magnus in order to give the script more weight, probably also the use of nitric acid. As early as 1225, Raymund von Lullius is said to have manufactured them in the factory by annealing saltpeter with clay, but this is unlikely from a chemical point of view. Later saltpetre was mixed with iron vitriol (FeSO4· 7H2O) heated, which gave higher yields at lower temperature.

J. R. Glauber won pure in the middle of the 17th century spiritus nitri by converting and distilling nitric acid with sulfuric acid, a laboratory process still used today for the production of nitric acid, which was also used in the Middle Ages aqua fortis or aqua valens and in the English-speaking world strong water was called. In the middle of the 18th century, A. L. Lavoisier recognized the chemical elements nitrogen and oxygen as components of nitric acid. The exact composition was determined by Henry Cavendish, who also succeeded in synthesizing it from the nitrogen in the air by means of electrical discharge.

Efficient manufacture did not begin until the beginning of the 19th century, when cheap sulfuric acid and Chile nitrate were available in sufficient quantities. “Air combustion” in an electric arc was also developed into a large-scale process (Birkeland – Eyde), which, however, was only competitive in countries with cheap electricity. The catalytic oxidation of ammonia over platinum was discovered by C. F. Kuhlmann (1838). Until the invention of ammonia synthesis by Haber and Bosch, however, ammonia remained too expensive compared to Chile's nitrate. 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 now replaced all other large-scale processes.


Nitric acid has been produced technically since 1908 using the Ostwald process. It is the catalytic oxidation of ammonia. The ammonia-air mixture is passed quickly (1/1000 s contact time) through hot platinum-rhodium networks (catalyst). At 800 ° C, nitrogen monoxide forms, which when cooled, reacts with excess oxygen to form nitrogen dioxide and then in trickle towers with water to form around 60% nitric acid. The 60% nitric acid can be concentrated up to 68% by distillation, which corresponds to the azeotrope with a boiling point maximum (122 ° C). Higher concentrations can be achieved by dehydration with magnesium nitrate (Mg (NO3)2) or by treatment with nitrous oxide (N.2O4) with the stoichiometrically required amount of air and water.

On a laboratory scale, fuming nitric acid can be produced by reacting concentrated sulfuric acid with alkali nitrates. Before 1908, nitric acid was obtained by this process using sodium nitrate (Chile's nitrate).



Nitric acid is in pure Colorless condition. Concentrated nitric acid, however, decomposes easily (especially when exposed to light) and, due to the nitrogen dioxide (NO2) often a yellowish or reddish hue. Pure nitric acid, which contains free nitrogen dioxide, is called fuming nitric acid. It contains over 90% ENT3 and has a strong oxidizing effect and can ignite some highly flammable substances. Nitric acid, which is colored yellow by dissolved nitrogen dioxide, can be discolored by a small amount of urea or, better, urea nitrate.

Nitric acid dissolves most metals. Exceptions are the precious metals gold, platinum and iridium. Aluminum, titanium, zirconium, hafnium, niobium, tantalum and tungsten are also resistant to passivation by nitric acid, with a firmly adhering, impermeable oxide layer forming on the metal. Since gold and silver could thus be separated, it became earlier Separating water called. Mixed with hydrochloric acid (aqua regia) it can also dissolve these precious metals. Furthermore, aluminum and iron are resistant to cold nitric acid as a result of passivation, and chromium to hot nitric acid.

When proteins that contain aromatic amino acids such as L-phenylalanine or L-tyrosine come into contact, they are colored yellow by the nitric acid and the benzene ring is nitrated. The reaction is called the xanthoprotein reaction and can be used to detect aromatic amino acids or proteins.

Physical properties of ENT3/H2O-mixtures depending on the concentration at 20 ° C and 1.013 bar

Wt% ENT3 0 10 20 30 40 50 60 70 80 90 100
(g / cm³)
1,00 1,05 1,12 1,18 1,25 1,31 1,37 1,42 1,46 1,48 1,513
1,00 1,04 1,14 1,32 1,55 1,82 2,02 2,02 1,84 1,47 0,88
Fp (° C) 0 -7 -17 -36 -30 -20 -22 -41 -39 -60 -42
Kp (° C) 100,0 101,2 103,4 107,0 112,0 116,4 120,4 121,6 116,6 102,0 86,0
p (ENT3) (mbar) 0,0 0,0 0,0 0,0 0,0 0,3 1,2 3,9 14,0 36,0 60,0
p (H2O) (mbar) 23,3 22,6 20,2 17,6 14,4 10,5 6,5 3,5 1,2 0,3 0,0
ENT3 (minor) 13,0 15,8 18,5 24,01


Nitric acid is one of the most important raw materials in the chemical industry. She serves:

  • in the form of their salts (nitrates) as fertilizers and for explosives,
  • as silver nitrate for the photo industry,
  • as Separating water for the separation (quartation) of gold and silver (silver is dissolved)
  • in mixtures with hydrochloric acid as aqua regia for dissolving gold as well as for gilding and for the detection of gold
  • for pickling and burning metals (graphic and galvanic technology),
  • for the nitration of organic substances in the production of dyes, medicines, explosives and disinfectants,
  • in the form of their esters for the production of explosives (blasting oil), celluloid, nitro and zapon varnishes,
  • for polishing metals.

Mixtures with sulfuric acid (two parts sulfuric acid and one part nitric acid) are called nitrating acid and are used for the nitration of organic compounds.

It was used as an oxidizer in rocket technology until the late 1980s (e.g. in the Agena upper stage).

Since nitric acid can convert the amino groups in the bases (adenine, thymine, guanine, cytosine) of DNA into hydroxyl groups, it has recently been used to create mutations in DNA. Because of this property of nitric acid, it is considered carcinogenic.


Nitric acid can be detected by means of nitrate detection using the ring test and Lunge's reagent. These detection methods are also referred to as classic methods.

See also


  1. abcdefGHi Safety data sheet (Merck) (the information applies to 100% nitric acid)
  2. BGIA-Gestis hazardous substance database

Categories: Oxidising substances | Corrosive substance | Mineral acid | Nitrogen compound | nitrate