Nitric acid

The nitrogen dioxide present.

History

The synthesis of Nitric Acid was first recorded circa 800 AD by the Arabic alchemist Jabir ibn Hayyan. [2]

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:

4HNO₃ → 2H₂O + 4NO₂ + O₂ (72°C)

which means that anhydrous nitric acid should be stored below 0°C to avoid decomposition. The nitrogen dioxide (NO₂) 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".^{[citation needed]}

Nitric acid is miscible with water in all proportions and azeotrope with a concentration of 68% HNO₃ and a boiling temperature of 120.5°C at 1 atm. Two solid hydrates are known; the monohydrate (HNO₃·H₂O) and the trihydrate (HNO₃·3H₂O).

Nitrogen oxides (NO_x) 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.

Chemical properties

Nitric acid is a strong acid that ionises almost completely in water, and a powerful oxidizing agent that also organic compounds and a monoprotic acid because there is only one dissociation.

Acidic properties

Being a typical acid, nitric acid reacts with alloys.

Nitric acid has an hydronium ion, H₃O⁺.

HNO₃ + H₂O → H₃O⁺ + NO₃^-

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 nitrogen dioxide (NO₂).

Cu + 4HNO₃ → Cu(NO₃)₂ + 2NO₂ + 2H₂O

The acidic properties tend to dominate with dilute acid, coupled with the preferential formation of nitrogen oxide (NO).

3Cu + 8HNO₃ → 3Cu(NO₃)₂ + 2NO + 4H₂O

Since nitric acid is an oxidizing agent, calcium (Ca) react with cold, dilute nitric acid to give hydrogen:

Mg_(s) + 2HNO_{3 (aq)} → Mg(NO₃)_{2 (aq)} + H_{2 (g)}

Passivation

Although passivation.

Reactions with non-metals

Reaction with non-metallic elements, with the exception of nitrogen dioxide for concentrated acid and nitrogen oxide for dilute acid.

C + 4HNO₃ → CO₂ + 4NO₂ + 2H₂O

or

3C + 4HNO₃ → 3CO₂ + 4NO + 2H₂O

Synthesis and production

Nitric acid is made by mixing Wilhelm Ostwald.

In laboratory, nitric acid can be made from 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.

H₂SO₄ + KNO₃ → KHSO₄ + HNO₃

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 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 including 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. Ultrapure acid is required for such determination, because small amounts of metal ions could affect the result of the analysis.

It has additional uses in platinum.

Nitric acid is a component of acid rain.

Nitric acid is a powerful hypergolic (i.e., self-igniting).

Concentrated nitric acid dyes human skin yellow due to a reaction with the protein keratin. These yellow stains turn orange when neutralized.

One use for IWFNA is as an liquid fuel rockets.

One use for nitric acid is in a colorometric test to distinguish heroin and morphine.

Nitric acid is also used in school laboratory to perform experiments involving the testing of silver chloride remains.

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).

Incidents Involving

In December 2007, a Taiwan-bound freighter carrying 2,000 tons of nitric acid sank off the shore of South Korea. ^[1]

References

1. ^ (1977) "S. Korean rescuers find wreckage believed to be missing ship". CNN.com: [1]. Retrieved on 2007-12-26.