Dissolves nitric acid gold

nitric acid

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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 (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 or wall nitrate, barite nitrate, etc.

The pure acid is colorless and has a sharp, pungent odor. It is used, among other things, to manufacture fertilizers, dyes and explosives.

history

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· 5 H2O) and alum (KAl (SO4)2· 12 H.2O) should have won. In the 13th century, Albertus Magnus is said to have used nitric acid to separate gold and silver ("separating water"). However, many writings were ascribed to Albertus Magnus only to give them greater weight, probably including those on the use of nitric acid. Later saltpetre was mixed with iron vitriol (FeSO4· 7 H2O) 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 that is 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 area 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 electrical discharge.

Efficient production 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 technical 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.

Manufacturing

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 is formed, 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 rectification (dehydration) with sulfuric acid (H.2SO4) or with aqueous magnesium nitrate solution (Mg (NO3)2) or by treatment with dinitrogen tetroxide (N.2O4) with the stoichiometrically required amount of oxygen (or air) and water.

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

$ \ mathrm {\ NaNO_3 + \ H_2SO_4 \ longrightarrow \ NaHSO_4 + \ HNO_3} $

Frequently occurring contamination of the acid with halogens or hydrogen halides can be removed by adding silver nitrate and subsequent distillation. Anhydrous nitric acid is obtained, starting from an acid highly concentrated by distillation, by passing through inert gas or by distillation over phosphorus pentoxide or oleum.[8]

properties

Nitric acid is colorless in its pure state. 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 that contains free nitrogen dioxide is called fuming nitric acid. It contains over 90% ENT3, has a strong oxidizing effect and can ignite some highly flammable substances; therefore nitric acid from 70% is considered oxidizing. 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 also resist dissolution by nitric acid through passivation. A tightly adhering, impermeable oxide layer forms on the metal. Since gold and silver could be separated, it became earlier Separating water called. Mixed with hydrochloric acid (aqua regia) or selenic acid[9] it can also dissolve gold and platinum. Furthermore, as a result of passivation, aluminum and iron are resistant to cold nitric acid, and chromium to hot nitric acid.

Nitric acid turns proteins containing aromatic amino acids such as L-phenylalanine or L-tyrosine yellow by nitrating the benzene ring. This xanthoprotein reaction can be used to detect aromatic amino acids and proteins.

Wt% ENT3 0 10 20 30 40 50 60 70 80 90 100
density
(g / cm3)
1,00 1,05 1,12 1,18 1,25 1,31 1,37 1,42 1,46 1,48 1,513
viscosity
(mPas)
1,00 1,04 1,14 1,32 1,55 1,82 2,02 2,02 1,84 1,47 0,88
M.p. (° C) 0 −7 −17 −36 −30 −20 −22 −41 −39 −60 −42
Bp (° 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) 1,7 3,6 5,6 7,9 10,4 13,0 15,8 18,5 21 24,01

use

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 salt silver nitrate in 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 detecting gold
  • for pickling and burning metals (graphic and galvanic technology),
  • for the nitration of organic substances in the production of dyes, medicinal products, explosives and disinfectants,
  • in the form of their esters for the production of explosives (blasting oil), celluloid, nitro and zapon varnishes,
  • for changing fats (water solubility) for cleaning purposes,
  • for polishing metals.
  • As a component of rocket fuels (See WFNA and RFNA)

Mixtures with sulfuric 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).

proof

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.

safety instructions

Nitric acid has a strong irritant effect on the skin, respiratory tract and mucous membranes and is able to destroy living tissue (chemical burns). In high concentration it is a strong oxidizing agent and oxidizing agent.

See also

Individual evidence

  1. ↑ Thieme Chemistry (ed.): RÖMPP Online - Version 3.5. Georg Thieme Verlag KG, Stuttgart 2009.
  2. 2,02,12,22,32,42,52,6data sheet 100% nitric acid at Merck, accessed January 19, 2011.
  3. ↑ pKs Table CCI ETH
  4. 4,04,1Entry from the CLP regulation too CAS no. 7697-37-2 in the GESTIS substance database of the IFA (JavaScript required)
  5. ↑ data sheet Nitric acid from Sigma-Aldrich, accessed April 22, 2011.
  6. ↑ Since December 1, 2012, only GHS hazardous substance labeling has been permitted for substances. Until June 1, 2015, the R-phrases of this substance can still be used to classify preparations, after which the EU hazardous substance labeling is of purely historical interest.
  7. ↑ entry to CAS no. 7697-37-2 in the GESTIS substance database of the IFA, accessed on March 30, 2008 (JavaScript required).
  8. ↑ G. Brauer (ed.), Handbook of Preparative Inorganic Chemistry, 2nd ed., Vol. 1, Academic Press 1963, pp. 491-492.
  9. ↑ E. Riedel, Christoph Janiak: Inorganic Chemistry. 8th edition. de Gruyter, 2011, ISBN 3110225662, p. 458.
  10. ↑ M. Thiemann, E. Scheibler, K.W. Wiegand: Nitric Acid, Nitrous Acid, and Nitrogen Oxides in Ullmann's Encyclopedia of Technical Chemistry, 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim, doi: 10.1002 / 14356007.a17_293.