About Nitric acid

Nitric acid is a colorless, highly corrosive liquid and a very powerful oxidizing agent that in the highly pure state is not entirely stable and must be prepared from its azeotrope by distillation with concentrated sulfuric acid. Nitric acid gradually yellows because of decomposition to nitrogen dioxide. Solutions containing more than 80% nitric acid are called fuming nitric acids. It also can be called Acide nitrique; Acido nitrico; Acidum nitricum; Aqua fortis; Azotic acid; Azotowy kwas; Engraver's acid; Hydrogen nitrate; Kyselina dusicne; Nital; Nitric acid; Nitrous fumes; Nitryl hydroxide; Red fuming nitric acid; Salpetersaeure; Salpetersaure; Salpeterzuuroplossingen; UNII-411VRN1TV4.

1. History

The first mention of nitric acid is in Pseudo-Geber's De Inventione Veritatis, wherein it is obtained by calcining a mixture of niter, alum and blue vitriol. It was again described by Albert the Great in the 13th century and by Ramon Lull, who prepared it by heating niter and clay and called it "eau forte" (aqua fortis).

Glauber devised the process still used today to obtain it, namely by heating niter with strong sulfuric acid. In 1776 Lavoisier showed that it contained oxygen, and in 1785 Henry Cavendish determined its precise composition and showed that it could be synthesized by passing a stream of electric sparks through moist air.

2. Preparation of Nitric acid

Nitric acid is made by reacting nitrogen dioxide (NO2) with water.

3 NO2 + H2O → 2 HNO3 + NO

For many years it was made by the reaction of sulfuric acid and saltpeter, but this method is no longer used.

NaNO3 + H2SO4 → NaHSO4 + HNO3

It is now manufactured by combusting ammonia in air in the presence of a (platinum or other noble metal) catalyst, and the nitrogen oxides thus formed are oxidized further and absorbed in water to form nitric acid.

NH3 + 2O2 → HNO3 + H2O

3. Uses of Nitric acid

1). A solution of Nitric acid and alcohol, Nital, is used for etching of metals to reveal the microstructure.Nitric acid is also used in explosives, and is key to the manufacture of Nitroglycerin and RDX.

2). In a low concentration, it 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).

4. Safety

Nitric acid(CAS NO.7697-37-2) 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.