Nitric acid

Nitric acid (also known as aqua fortis and spirit of niter).
Molecular formula : HNO3
(O= 76,17 %, N= 22,23 %, H= 1,6 %)

Molar mass = 63,0128 ± 0,0012 g·mol^-1

It is a highly corrosive strong mineral acid. Nitric acid is the primary reagent used for nitration - the addition of a nitro group, typically to an organic molecule. While some resulting nitro compounds are shock- and thermally-sensitive explosives, a few are stable enough to be used in munitions and demolition, while others are still more stable and used as pigments in inks and dyes. Nitric acid is also commonly used as a strong oxidizing agent.
Nitric acid is a component of acid rain, which is formed by hydration of NO₂ nitrogen dioxide, a major air pollutant:

Normally, the nitric oxide produced by the reaction is reoxidized by the oxygen in air to produce additional nitrogen dioxide.

Preparation.
Production of nitric acid is via the Ostwald process, named after German chemist Wilhelm Ostwald. In this process, anhydrous ammonia is oxidized to nitric oxide, in the presence of platinum or rhodium gauze catalyst at a high temperature of about 226.9 °C (500 K, 440.3 °F) and a pressure of 9 bar:

Nitric oxide is then reacted with oxygen in air to form nitrogen dioxide.

This is subsequently absorbed in water to form nitric acid and nitric oxide.

The nitric oxide is cycled back for reoxidation. Alternatively, if the last step is carried out in air:

The aqueous HNO₃ obtained can be concentrated by distillation up to about 68% by mass. Further concentration to 98% can be achieved by dehydration with concentrated H2SO4.
By using ammonia derived from the Haber process, the final product can be produced from nitrogen, hydrogen, and oxygen which are derived from air and natural gas as the sole feedstocks.
The annual global production of nitric acid (by various processes) is of the order of 60 million tons.

Physical and chemical properties :
Commercially available nitric acid is an azeotrope with water at a concentration of 68% HNO₃, which is the ordinary concentrated nitric acid of commerce. This solution has a boiling temperature of 120.5 °C at 1 atm.
Two solid hydrates are known; the monohydrate (HNO₃·H₂O) and the trihydrate (HNO₃·3H₂O).
Nitric acid of commercial interest usually consists of the maximum boiling azeotrope of nitric acid and water, which is approximately 68% HNO₃, (approx. 15 molar). This is considered concentrated or technical grade, while reagent grades are specified at 70% HNO₃. The density of concentrated nitric acid is 1.42 g/mL. An older density scale is occasionally seen, with concentrated nitric acid specified as 42° Baumé.

Main properties (at 20 ° C and 1.013 bar) :
Nitric acid is normally considered to be a strong acid at ambient temperatures. There is some disagreement over the value of the acid dissociation constant, though the pKa value is usually reported as less than -1. This means that the nitric acid in solution is fully dissociated except in extremely acidic solutions. The pKa value rises to 1 at a temperature of 250 °C.

Mixed with hydrochloric acid, it forms "aqua regia", one of the few reagents capable of dissolving gold and platinum.

Commercial solutions.
Commercial grade nitric acid solutions are usually between 52% and 68% nitric acid.
When the solution contains more than 86% HNO3, it is referred to as fuming nitric acid. Depending on the amount of nitrogen dioxide present, fuming nitric acid is further characterized as white fuming nitric acid or red fuming nitric acid, at concentrations above 95%.

A formulation for the water treatment.
Reaction mechanism of calcium bicarbonates (simplified equations):

With 1 mg as HNO3 added, there has (10/63) = 0.15 °f for lower TAC (Alkalinity), and 1.396 mg as free CO2 and 1.58 mg/L as NO₃ formed.

Storage.
Takes place in containers inxoydables steel or amuminium for over 80% levels.
Glass containers for small volumes.
Non-compatible materials: nichel, copper.

Uses.
The main industrial use of nitric acid is for the production of fertilizers. Nitric acid is neutralized with ammonia to give ammonium nitrate. This application consumes 75–80% of the 26M tons produced annually (1987). The other main applications are for the production of explosives, nylon precursors, and specialty organic compounds.

• Wastewater and industrial treatment (as dilute aqueous solutions).
• 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).
• The corrosive effects of nitric acid are exploited for a number of specialty applications, such as pickling stainless steel. A solution of nitric acid, water and alcohol, Nital, is used for etching of metals to reveal the microstructure. ISO 14104 is one of the standards detailing this well known procedure.
• 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). The phosphoric acid content helps to passivate ferrous alloys against corrosion by the dilute nitric acid.
• Nitric acid can be used as a spot test for alkaloids like LSD, giving a variety of colours depending on the alkaloid.
• In organic synthesis, industrial and otherwise, the nitro group is a versatile functionality. Most derivatives of aniline are prepared via nitration of aromatic compounds followed by reduction. Nitrations entail combining nitric and sulfuric acids to generate the nitronium ion, which electrophilically reacts with aromatic compounds such as benzene. Many explosives, e.g. TNT, are prepared in this way.
• Nitric acid has been used in various forms as the oxidizer in liquid-fueled rockets.
  These forms include red fuming nitric acid, white fuming nitric acid, mixtures with sulfuric acid, and these forms with HF inhibitor. IRFNA (inhibited red fuming nitric acid) was one of 3 liquid fuel components for the US BOMARC missile.

Health-wise.
Nitric acid is a strong acid and a powerful oxidizing agent. The major hazard posed by it is chemical burns as it carries out acid hydrolysis with proteins (amide) and fats (ester) which consequently decomposes living tissue (e.g. skin and flesh). Concentrated nitric acid stains human skin yellow due to its reaction with the keratin. These yellow stains turn orange when neutralized. Systemic effects are unlikely, however, and the substance is not considered a carcinogen or mutagen.
The standard first aid treatment for acid spills on the skin is, as for other corrosive agents, irrigation with large quantities of water. Washing is continued for at least ten to fifteen minutes to cool the tissue surrounding the acid burn and to prevent secondary damage. Contaminated clothing is removed immediately and the underlying skin washed thoroughly.
Being a strong oxidizing agent, reactions of nitric acid with compounds such as cyanides, carbides, metallic powders can be explosive and those with many organic compounds, such as turpentine, are violent and hypergolic (i.e. self-igniting). Hence, it should be stored away from bases and organics.

Toxicological profile (French) - Acide nitrique (FT 9) - Institut national de recherche et de sécurité (INRS).

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