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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 (HNO3), otherwise known as aqua fortis, is a
colorless, corrosive liquid, a toxic acid which can cause severe burns. If the solution
contains more than 86% nitric acid, it is referred to as fuming nitric acid, and can be
separated into two kinds of fuming acids, white fuming nitric acid and red fuming nitric
acid.
Contents
" 1 History
" 2 Chemistry
" 3 Synthesis and Production
" 4 Uses
" 5 References
" 6 External links
History
Nitric acid was first synthesized circa 800 AD by alchemist Jabir ibn Hayyan, who also
invented modern distillation and numerous other basic chemical processes still in use
today.
Chemistry
Nitric acid is a strong acid with a pKa of -2: in aqueous solution, it completely dissociates
into the nitrate ion NO3- and a hydrated proton, known as a hydronium ion, H3O+. 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.
At room temperature nitric acid gives off red or yellow fumes.
Nitric acid and its salts, the nitrates, should not be confused with nitrous acid and its salts,
the nitrites.
Synthesis and Production
Nitric acid is made by mixing nitrogen dioxide (NO2) with water. Creating a very pure
nitric acid usually involves distillation with sulfuric acid, as nitric acid forms an
azeotrope with water with a composition of 68% nitric acid and 32% water. 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 by reacting 200 g of potassium nitrate (KNO3) in 106 ml of 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.
The dissolved NOx 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).
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.
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 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. Yet these yellow stains turn orange when alkalised.
The use for IFWNA is as an oxidizer in liquid fuel rockets.
Ostwald process
The Ostwald process is chemical process for producing nitric acid, which was developed
by Wilhelm Ostwald (patented 1902). It is a mainstay of the modern chemical industry.
Historically and practically it is closely associated with the Haber process, which
provides the requisite raw material, ammonia.
Description
Ammonia is converted to nitric acid in two stages. It is oxidized (in a sense "burned") by
heating with oxygen in the presence of a catalyst of platinum with 10% rhodium, to form
nitric oxide and water. This step is strongly exothermic, making it a useful heat source
once initiated ("H = -950 kJ):
4 NH3(g) + 5 O2(g) ’! 4 NO(g) + 6 H2O(g)
Stage two (combining two reaction steps) is carried out in the presence of water in an
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Dobre pomysły nie mają przeszłości, mają tylko przyszłość. Robert Mallet
De minimis - o najmniejszych rzeczach.
Dobroć jest ważniejsza niż mądrość, a uznanie tej prawdy to pierwszy krok do mądrości. Theodore Isaac Rubin
Dobro to tylko to, co szlachetne, zło to tylko to, co haniebne.
Dla człowieka nie tylko świat otaczający jest zagadką; jest on nią sam dla siebie. I z obu tajemnic bardziej dręczącą wydaje się ta druga. Antoni Kępiński (1918-1972)
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