Nitric Acid

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Nitric acid is a highly reactive oxidizing agent used in making fertilizers, explosives, and rocket fuels, and in a wide variety of industrial metallurgical processes. It is also a component of acid rain. Its chemical formula is HNO3 and it has been known as “aqua fortis”, which means strong water, to alchemists. It is a transparent, colorless to yellowish, fuming corrosive liquid. Nitric acid is a strong acid and therefore it completely dissociates in water. It has a gravity of 1.41 and the concentration of the hydronium ions(1) yields a pH of 0.7. Its boiling point is 122C and its melting point is -42C.

It was first mentioned by Pseuso-Geber, a European alchemist born in the 13th century. Described by Albert the Great in the 13th century and named by Ramon Lull, who prepared it and called it “eau forte” (aqua fortis). There were people saying that it was discovered by Joseph-Louis Gay-Lussac or Johann Rudolf, but nobody knows who really did discover that.

As it is a intoxicating, oxidizing acid, it reacts most with metals, but does not react with pure gold. However, noble metals could be oxidized and dissolved by nitric acid which leads to colour changes of gold-alloy surface. So nitric acid is used in jewelry shops to spot low-gold alloys (< 14 carats(2)) and to asses the gold purity. Nitric acid also reacts powerfully with most of the organic material, which may also explode. It reacts with non-metallic elements except for nitrogen, oxygen, noble gases, silicon and halogens. It oxides them to their highest oxidation states(3) as acids with the formation of nitrogen dioxide for concentrated acid and nitric oxide for dilute acid. Chromium (Cr), iron (Fe) and aluminium (Al) dissolve in dilute nitric acid, which the concentrated acid forms a metal oxide layer that protects the metal from further oxidation, and it is called passivation.

Nitric acid can be made in laboratory or industrially. In laboratory, nitric acid can be made from...
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