Nitric acid

The chemical compound nitric acid (HNO₃) is a viscous and corrosive liquid that can cause severe burns to living beings and animals. It is used as a laboratory reagent and to make explosives such as nitroglycerin and trinitrotoluene (TNT), as well as fertilizers such as ammonium nitrate. It has additional uses in metallurgy and refining, as it reacts with most metals, and in chemical synthesis. When mixed with hydrochloric acid it forms aqua regia, a rare reagent capable of dissolving gold and platinum. Nitric acid is also a component of acid rain.

Summary

Nitric acid is obtained by mixing dinitrogen pentoxide (N₂O₅) and water. Synthesizing pure nitric acid typically requires distillation with sulfuric acid, as nitric acid forms an azeotrope with water in a composition of 68% nitric acid and 32% water. Commercial solutions include 52-68% nitric acid. If the solution contains more than 86% nitric acid it is called fuming nitric acid and comes in two varieties, white and red. Fuming white nitric acid is also called 100% as it has almost no water (less than 1%) depending on the process.

Industrially, it is manufactured through the synthesis of ammonia and oxygen. Both elements are combined in a large reactor in the presence of a metallic catalyst. Due to the high temperatures that are withstood (700-900 °C), metals that maintain their physical characteristics at these temperatures are used, platinum being the most appropriate, in combination with rhodium (5-10%), which gives it more rigidity..

Properties

Physical properties

Pure nitric acid is a colorless, odorless, viscous liquid. Often various impurities color it yellow-brown. At room temperature it releases yellow fumes. Concentrated nitric acid stains human skin yellow on contact, due to the presence of aromatic groups present in the keratin of the skin.

• Evaporation point: 83 °C
• Fusion point: −41.6 °C
• Relative density (water = 1): 1.4
• Solubility in water: miscible
• Vapor pressure at 20 °C: 6,4 kPa
• Relative density of steam (air = 1): 2,2

Chemical Properties

Nitric acid is a powerful oxidizing agent; its reactions with compounds such as cyanides, carbides, and metal powders can be explosive. The reactions of nitric acid with many organic compounds, such as turpentine, are violent, the mixture being hypergolic (ie self-igniting). It is a strong oxacid: in aqueous solution it completely dissociates into a nitrate ion NO₃^- and a hydric proton. The salts of nitric acid (containing the nitrate ion) are called nitrates.

Applications

1. As a nitrating agent in the manufacture of explosives.
2. In the manufacture of fertilizers. Amonic nitrosulphate is a simple nitrogen abono obtained chemically from the reaction of nitric and sulfuric acid with ammonia.
3. Nitric acid is used in some cases in the passive process.
4. The nitric acid is used in artistic engraving (cooter), also used to check gold and platinum.
5. In the electronic industry, it is used in the production of printed circuit boards (PCBs).
6. In the pharmaceutical industry it is used as a separator of highly basic compounds in organic media.

History

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

In 1650, Glauber devised a process to obtain it by distilling potassium nitrate with 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 humid air.