Nitric acid

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Nitric acid
Image:Nitric-acid.png Image:Nitric-acid-3D-vdW.png
General
Systematic name	Nitric acid
Other names	Aqua fortis Spirit of nitre
Molecular formula	H NO₃
SMILES	[N+](=O)(O)[O-]
Acidic Ion Concentration	pH = -2 (1 N)
Molar mass	63.01 g/mol
Appearance	Clear, colorless liquid
CAS number	7697-37-2
Properties
Density and phase	1.51 g/cm³
Solubility in water	miscible
Melting point	-42 °C (231 K)
Boiling point	83 °C (356 K)
Acidity (pK_a)	-2
Viscosity	? cP at ? °C
Structure
Molecular shape	trigonal planar
Dipole moment	? D
Hazards
MSDS	External MSDS
EU classification	Oxidant (O) Corrosive (C)
NFPA 704	Image:NFPA 704.svg 0 3 0 OX
R-phrases	R8, R35
S-phrases	S1/2, S23, S26, S36, S45
Flash point	not applicable
RTECS number	QU5775000
Supplementary data page
Structure and properties	n, ε_r, etc.
Thermodynamic data	Phase behaviour Solid, liquid, gas
Spectral data	UV, IR, NMR, MS
Related compounds
Related compounds	Nitrous acid Dinitrogen pentoxide
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references

The chemical compound nitric acid (H N O₃), otherwise known as aqua fortis or spirit of nitre, is an aqueous solution of hydrogen nitrate (anhydrous nitric acid). It is a highly corrosive and toxic acid that can cause severe burns. Colorless when pure, older samples tend to acquire a yellow cast due to the accumulation of 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 nitrogen dioxide present.

1 History
2 Chemistry
3 Synthesis and production
4 Uses
5 External links

[edit] History

Nitric acid was first synthesized circa 800 AD by alchemist Jabir ibn Hayyan. ^{[citation needed]}

[edit] Chemistry

Nitric acid is a strong acid with an acid dissociation constant (pK_a) of −2: in aqueous solution, it completely ionizes into the nitrate ion NO₃⁻ and a hydrated proton, known as a hydronium ion, H₃O⁺. Nitric Acid is a monoprotic acid because there is only one dissociation. The salts of nitric acid (which contain the nitrate ion) are also known as nitrates. The overwhelming majority of them are very soluble in water and in other polar liquid substances, such as ethanol.

At room temperature nitric acid gives off red or yellow fumes, and is subject to partial decomposition when distilled at atmospheric pressure.

Nitric acid and its salts, the nitrates, should not be confused with nitrous acid and its salts, the nitrites.

[edit] Synthesis and production

Nitric acid is made by mixing nitrogen dioxide (N O₂) 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 azeotropic mixture with 32% water. Further concentration involves distillation with sulfuric acid which acts as a dehydrating agent. On a laboratory scale, such distillation must be done in all glass apparatus at reduced pressure, to prevent decomposition of the acid. Rubber and cork fittings should also be avoided as nitric acid attacks these materials. Commercial grade nitric acid solutions are usually between 52% and 68% nitric acid. Commercial production of nitric acid is via the Ostwald process after Wilhelm Ostwald.

Nitric acid can be made from Copper(II) nitrate or by reacting approximately equal masses of potassium nitrate (KNO₃) with 96% sulfuric acid (H₂SO₄), and distilling this mixture at nitric acid's boiling point of 83 °C until only a white crystalline mass, potassium hydrogen sulfate (KHSO₄), remains in the reaction vessel. The obtained red fuming nitric acid may be converted to the white nitric acid. Note that in a laboratory setting, it is necessary to use all-glass equipment, ideally a one-piece retort, because anhydrous nitric acid attacks cork, rubber, and skin, and leaks can be extremely dangerous.

The dissolved NO_x are readily removed using reduced pressure at room temperature (10-30 min at 200 mmHg or 27 kPa). Obtained white fuming nitric acid has density 1.51 g/cm³. This procedure can also be performed under reduced pressure and temperature in one step in order to produce less nitrogen dioxide gas.

The acid can also be synthesized by oxidizing ammonia, but the product is diluted by the water also formed as part of the reaction. However, this synthesization 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.

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 NO₂. Red fuming nitric acid, or RFNA, contains substantial quantities of dissolved nitrogen dioxide (NO₂) leaving the solution with a reddish-brown color. One formulation of RFNA specifies a minimum of 17% NO₂, another specifies 13% NO₂. In either event, an inhibited fuming nitric acid (either IWFNA, or IRFNA) can be made by the addition of 0.6 to 0.7% hydrogen fluoride, HF. This fluoride is added for corrosion resistance in metal tanks (the fluoride creates a metal fluoride layer that protects the metal).

[edit] Uses

Commonly used as a laboratory reagent, nitric acid is used in the manufacture of explosives such as nitroglycerin, trinitrotoluene (TNT) and Cyclotrimethylenetrinitramine (RDX), as well as fertilizers such as ammonium nitrate.

Also, in ICP-MS and ICP-AES techniques, nitric acid (with a concentration from 0.5% to 2.0%) is used as a matrix compound for determining metal traces in solutions. An ultrapure acid is needed for such determination, because any small amount of metal ions could affect the result of the analysis.

It has additional uses in metallurgy and refining as it reacts with most metals, and in organic syntheses. When combined with hydrochloric acid, it forms aqua regia, one of the few reagents capable of dissolving gold and platinum.

Nitric acid was also used by the ancient egyptians. When nitric acid comes into contact with gold(Au), it stains the skin a bright purple.

Nitric acid is also a component of acid rain.

Nitric acid is a very powerful oxidizing agent, and the reactions of nitric acid with compounds such as cyanides, carbides, 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 on contact, due to interactions with the skin protein keratin. These yellow stains turn orange when neutralized.

One use for IWFNA is as an oxidizer in liquid fuel rockets.

One use for nitric acid is in a colorometric test to tell the difference between heroin and morphine.

Nitric acid is also used in school laboratory to perform experiments involving the testing of chloride. The sample is added with silver nitrate solution and nitric acid to see if a white precipitate, silver chloride is left behind.