Nitric acid 21655 225717289 2008-07-15T01:40:00Z 76.17.134.215 /* Uses */ {{Chembox new | Name = Nitric acid | ImageFile = Nitric acid resonance median.png | ImageSize = 150px | ImageFileL1 = Nitric-acid-2D-dimensions.png | ImageSizeL1 = 150px | ImageFileR1 = Nitric-acid-3D-balls-B.png | ImageSizeR1 = 150px | IUPACName = Nitric acid | OtherNames = ''Aqua fortis''; ''Spirit of nitre''; ''Salpetre acid''; ''Hydrogen Nitrate'' | Section1 = {{Chembox Identifiers | SMILES = O[N+](=O)[O-] | CASNo = 7697-37-2 | RTECS = QU5775000 }} | Section2 = {{Chembox Properties | Formula = [[Hydrogen|H]][[nitrate|NO<sub>3</sub>]] | MolarMass = 63.012 g/mol | Appearance = Clear, colorless liquid | Density = 1.51 g/cm³, colorless liquid | Solubility = miscible | MeltingPtC = -42 | BoilingPtC = 83 | Boiling_notes = bp of pure acid. 68% solution boils at 120.5°C | Acidity (p''K''<sub>a</sub>) = -1.4 | Viscosity = ? [[Poise|cP]] at ? °C | Dipole = 2.17 ± 0.02 [[Debye|D]] }} | Section7 = {{Chembox Hazards | FlashPt = not applicable | EUClass = Oxidant ('''O''')<br/>Corrosive ('''C''') | RPhrases = {{R8}}, {{R35}} | SPhrases = {{S1/2}}, {{S23}}, {{S26}}, {{S36}}, {{S45}} }} | Section8 = {{Chembox Related | OtherCpds = [[Nitrous acid]]<br/>[[Dinitrogen pentoxide]]}} }} '''Nitric acid''' ([[Hydrogen|H]][[nitrate|NO<sub>3</sub>]]), also known as '''''aqua fortis''''' and '''spirit of nitre''', is a highly [[corrosion|corrosive]] and [[toxic]] [[strong acid]] that can cause severe burns. The synthesis of nitric acid was first recorded circa [[800]] [[Common Era|AD]] by the [[alchemy|alchemist]] [[Jabir ibn Hayyan]]. <ref>[http://www.windows.ucar.edu/tour/link=/physical_science/chemistry/nitric_acid.html&edu=high Nitric Acid<!-- Bot generated title -->]</ref> Colorless when pure, older samples tend to acquire a yellow cast due to the accumulation of [[nitrogen oxide|oxides of nitrogen]]. If the solution contains more than 86% nitric acid, it is referred to as '''fuming nitric acid'''. Fuming nitric acid is characterized as [[white fuming nitric acid]] and [[red fuming nitric acid]], depending on the amount of [[dinitrogen tetroxide|nitrogen dioxide]] present. ==Properties== Pure anhydrous nitric acid (100%) is a colorless liquid with a density of 1522 kg/m³ which solidifies at -42 °C to form white crystals and boils at 83 °C. When boiling in light, even at room temperature, there is a partial [[decomposition]] with the formation of nitrogen dioxide following the reaction: :4HNO<sub>3</sub> → 2H<sub>2</sub>O + 4NO<sub>2</sub> + O<sub>2</sub> (72°C) which means that anhydrous nitric acid should be stored below 0 °C to avoid decomposition. The [[nitrogen dioxide]] (NO<sub>2</sub>) remains dissolved in the nitric acid coloring it yellow, or red at higher temperatures. While the pure acid tends to give off white fumes when exposed to air, acid with dissolved nitrogen dioxide gives off reddish-brown vapours, leading to the common name "red fuming acid" or "fuming nitric acid". {{Fact|date=April 2007}} Nitric acid is [miscible] with water in all proportions and [[distillation]] gives an [[azeotrope]] with a concentration of 68% HNO<sub>3</sub> and a boiling temperature of 120.5 °C at 1 atm. Two solid hydrates are known; the monohydrate (HNO<sub>3</sub>·H<sub>2</sub>O) and the trihydrate (HNO<sub>3</sub>·3H<sub>2</sub>O). [[Nitrogen oxide]]s (NO<sub>x</sub>) are soluble in nitric acid and this property influences more or less, all the physical characteristics depending on the concentration of the oxides. These mainly include the vapor pressure above the liquid and the boiling temperature, as well as the color mentioned above. Nitric acid is subject to [[thermal]] or light decomposition with increasing [[concentration]] and this may give rise to some non-negligible variations in the vapour pressure above the liquid because the nitrogen oxides produced dissolve partly or completely in the acid. ===Acidic properties=== Being a typical acid, nitric acid reacts with [[alkali]]s, [[basic oxide]]s, and [[carbonate]]s to form [[salts]], such as [[ammonium nitrate]]. Due to its oxidizing nature, nitric acid generally does not donate its proton (that is, it does not liberate [[hydrogen]]) on reaction with [[metal]]s and the resulting salts are usually in the higher oxidized states. For this reason, heavy [[corrosion]] can be expected and should be guarded against by the appropriate use of corrosion resistant metals or [[alloy]]s. Nitric acid has an [[acid dissociation constant]] (pK<sub>a</sub>) of −1.4: in [[water|aqueous]] [[solution]], it almost completely (93% at 0.1 mol/L) [[ionizes]] into the [[nitrate]] [[ion]] NO<sub>3</sub><sup>−</sup> and a [[hydrated]] [[proton]], known as a [[hydronium]] ion, H<sub>3</sub>O<sup>+</sup>. :HNO<sub>3</sub> + H<sub>2</sub>O → H<sub>3</sub>O<sup>+</sup> + NO<sub>3</sub><sup>-</sup> ===Oxidizing properties=== ====Reactions with metals==== Being a powerful oxidizing agent, nitric acid reacts violently with many organic materials and the reactions may be explosive. Depending on the acid concentration, temperature and the reducing agent involved, the end products can be variable. Reaction then takes place with all metals except the [[precious metal]] series and certain alloys. As a general rule of course, oxidizing reactions occur primarily with the concentrated acid, favouring the formation of [[nitrogen dioxide]] (NO<sub>2</sub>). :Cu + 4HNO<sub>3</sub> → Cu(NO<sub>3</sub>)<sub>2</sub> + 2NO<sub>2</sub> + 2H<sub>2</sub>O The acidic properties tend to dominate with dilute acid, coupled with the preferential formation of [[nitrogen oxide]] (NO). :3Cu + 8HNO<sub>3</sub> → 3Cu(NO<sub>3</sub>)<sub>2</sub> + 2NO + 4H<sub>2</sub>O Since nitric acid is an oxidizing agent, [[hydrogen]] (H<sub>2</sub>) is rarely formed. Only [[magnesium]] (Mg), Manganese (Mn) and [[calcium]] (Ca) react with ''cold'', ''dilute'' nitric acid to give hydrogen: :Mg<sub>(s)</sub> + 2HNO<sub>3 (aq)</sub> → Mg(NO<sub>3</sub>)<sub>2 (aq)</sub> + H<sub>2 (g)</sub> ====Passivation==== Although [[chromium]] (Cr), [[iron]] (Fe) and [[aluminium]] (Al) readily dissolve in dilute nitric acid, the concentrated acid forms a metal oxide layer that protects the metal from further oxidation, which is called [[passivation]]. ====Reactions with non-metals==== Reaction with non-metallic elements, with the exception of [[silicon]] and [[halogens]], usually oxidizes them to their highest [[Oxidation number|oxidation state]]s as acids with the formation of [[nitrogen dioxide]] for concentrated acid and [[nitrogen oxide]] for dilute acid. :C + 4HNO<sub>3</sub> → CO<sub>2</sub> + 4NO<sub>2</sub> + 2H<sub>2</sub>O or :3C + 4HNO<sub>3</sub> → 3CO<sub>2</sub> + 4NO + 2H<sub>2</sub>O ==Grades== White fuming nitric acid, also called 100% nitric acid or WFNA, is very close to the anhydrous nitric acid product. One specification for white fuming nitric acid is that it has a maximum of 2% water and a maximum of 0.5% dissolved NO<sub>2</sub>. Red fuming nitric acid, or RFNA, contains substantial quantities of dissolved nitrogen dioxide (NO<sub>2</sub>) leaving the solution with a reddish-brown color. One formulation of RFNA specifies a minimum of 17% NO<sub>2</sub>, another specifies 13% NO<sub>2</sub>. An ''inhibited'' fuming nitric acid (either IWFNA, or IRFNA) can be made by the addition of 0.6 to 0.7% [[hydrofluoric acid|hydrogen fluoride]], HF. This fluoride is added for corrosion resistance in metal tanks (the fluoride creates a metal fluoride layer that protects the metal). ==Industrial production== {{Unreferenced|date=January 2008}} Nitric acid is made by mixing [[nitrogen dioxide]] (NO<sub>2</sub>) with [[water]] in the presence of oxygen or air to oxidize the [[nitrous acid]] also produced by the reaction. Dilute nitric acid may be concentrated by distillation up to 68% acid, which is an [[azeotrope|azeotropic]] mixture with 32% water. Further concentration involves distillation with [[sulphuric acid]] which acts as a dehydrating agent. In the laboratory, such distillations must be done with all-glass apparatus at reduced pressure, to prevent decomposition of the acid. Commercial grade nitric acid solutions are usually between 52% and 68% nitric acid. Commercial production of nitric acid is via the [[Ostwald process]], named after [[Wilhelm Ostwald]]. The acid can also be synthesized by oxidizing [[ammonia]], but the product is [[concentration|diluted]] by the water also formed as part of the reaction. However, this method is important in producing [[ammonium nitrate]] from ammonia derived from the [[Haber process]], because the final product can be produced from nitrogen, hydrogen, and oxygen as the sole feedstocks. ==Laboratory synthesis== In laboratory, nitric acid can be made from [[copper(II) nitrate]] or by reacting approximately equal masses of [[potassium nitrate]] (KNO<sub>3</sub>) with 96% [[sulfuric acid]] (H<sub>2</sub>SO<sub>4</sub>), and [[distilling]] this mixture at nitric acid's boiling point of 83 °C until only a white crystalline mass, [[potassium hydrogen sulfate]] (KHSO<sub>4</sub>), remains in the reaction vessel. The obtained red fuming nitric acid may be converted to the white nitric acid. :H<sub>2</sub>SO<sub>4</sub> + KNO<sub>3</sub> → KHSO<sub>4</sub> + HNO<sub>3</sub> The dissolved [[NOx|NO<sub>x</sub>]] are readily removed using reduced pressure at room temperature (10-30 min at 200 [[torr|mmHg]] or 27 [[kilopascal|kPa]]) to give white fuming nitric acid. This procedure can also be performed under reduced pressure and temperature in one step in order to produce less [[nitrogen dioxide]] gas.{{Fact|date=January 2008}} ==Uses== [[Image:Nitric acid lab.jpg|thumb|300px|right|Nitric acid in a laboratory.]] IWFNA may be used as the [[oxidation|oxidizer]] in [[rocket fuel|liquid fuel rocket]]s.{{Fact|date=January 2008}} IRFNA was one of 3 liquid fuel components for the [[BOMARC]] missile <ref>[http://www.techbastard.com/missile/bomarc/summary.php BOMARC Summary<!-- Bot generated title -->]</ref> A solution of nitric acid and alcohol, [[Nital]], is used for etching of metals to reveal the microstructure. Commercially available aqueous blends of 5-30% nitric acid and 15-40% phosphoric acid are commonly used for cleaning food and dairy equipment primarily to remove precipitated calcium and magnesium compounds (either deposited from the process stream or resulting from the use of hard water during production and cleaning). Nitric acid is also used in explosives, and is one of the key components of [[Nitroglycerin]] and [[RDX]]. ===Digestion=== In [[elemental analysis]] by [[ICP-MS]], [[ICP-AES]], GFAA, and Flame AA, dilute nitric acid (0.5 to 5.0 %) is used as a matrix compound for determining metal traces in solutions.<ref>Standard Methods for the Examination of Water and Wastewater, 20 edition,APHA, AWWA, WEF, 1998</ref> Ultrapure acid is required for such determination, because small amounts of metal ions could affect the result of the analysis. ===Woodworking=== In a low concentration (approximately 10%), nitric acid is often used to artificially age [[pine]] and [[maple]]. The color produced is a grey-gold very much like very old wax or oil finished wood ([[wood finishing]]). <ref>http://books.google.com/books?id=CMJvfh2IUSYC&printsec=frontcover&dq</ref> ===Other uses=== Alone, it is useful in [[metallurgy]] and [[refining]] as it reacts with most [[metal]]s, and in [[chemical synthesis|organic syntheses]]. When mixed with [[hydrochloric acid]], nitric acid forms [[aqua regia]], one of the few reagents capable of dissolving [[gold]] and [[platinum]]. ==Safety== Nitric acid is a powerful [[oxidizing agent]], and the reactions of nitric acid with compounds such as [[cyanide]]s, [[carbide]]s, and metallic powders can be [[explosive]]. Reactions of nitric acid with many organic compounds, such as [[turpentine]], are violent and [[hypergolic]] (i.e., self-igniting). Concentrated nitric acid dyes human [[skin]] yellow due to a reaction with the [[keratin]]. These yellow stains turn orange when neutralized.<ref>[http://www.chm.bris.ac.uk/motm/nitric/nitrich.htm Nitric Acid - MOTM November 2007 - HTML only version<!-- Bot generated title -->]</ref> ==References== <references/> ==External links== * [http://www.ilo.org/public/english/protection/safework/cis/products/icsc/dtasht/_icsc01/icsc0183.htm International Chemical Safety Card 0183] * [http://www.cdc.gov/niosh/npg/npgd0447.html NIOSH Pocket Guide to Chemical Hazards] * {{ecb}} * [http://www.npi.gov.au/database/substance-info/profiles/65.html National Pollutant Inventory - Nitric Acid Fact Sheet] * [http://www.efma.org/publications/NitricAcid/Section03.asp Properties and classification of nitric acid] [[Category:Nitrates]] [[Category:Acids]] [[ar:حمض نتريك]] [[bs:Dušična kiselina]] [[br:Trenkenn nitrek]] [[bg:Азотна киселина]] [[ca:Àcid nítric]] [[cs:Kyselina dusičná]] [[da:Salpetersyre]] [[de:Salpetersäure]] [[et:Lämmastikhape]] [[es:Ácido nítrico]] [[eo:Nitrata acido]] [[fr:Acide nitrique]] [[ko:질산]] [[id:Asam nitrat]] [[is:Saltpéturssýra]] [[it:Acido nitrico]] [[he:חומצה חנקתית]] [[lv:Slāpekļskābe]] [[lt:Azoto rūgštis]] [[hu:Salétromsav]] [[mk:Азотна киселина]] [[ms:Asid nitrik]] [[nl:Salpeterzuur]] [[ja:硝酸]] [[no:Salpetersyre]] [[nn:Salpetersyre]] [[pl:Kwas azotowy(V)]] [[pt:Ácido nítrico]] [[ro:Acid azotic]] [[ru:Азотная кислота]] [[sk:Kyselina dusičná]] [[sl:Dušikova kislina]] [[sr:Азотна киселина]] [[sh:Azotna kiselina]] [[fi:Typpihappo]] [[sv:Salpetersyra]] [[th:กรดไนตริก]] [[vi:Axit nitric]] [[tr:Nitrik asit]] [[uk:Азотна кислота]] [[zh:硝酸]]