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Nitric acid (HNO3) , also known as aqua fortis (Latin for “strong water”) and spirit of niter, is a highly corrosive mineral acid
The pure compound is colorless, but older samples tend to acquire a yellow cast due to decomposition into oxides of nitrogen and water. Most commercially available nitric acid has a concentration of 68% in water. When the solution contains more than 86% HNO۳ , it is referred to as fuming nitric acid. Depending on the amount of nitrogen dioxide present , fuming nitric acid is further characterized as red fuming nitric acid at concentrations above 86%, or white fuming nitric acid at concentrations above 95%
Physical and chemical properties
Commercially available nitric acid is an azeotrope with water at a concentration of 68% HNO3. This solution has a boiling temperature of 120.5 °C at 1 atm. It is known as “concentrated nitric acid”. Pure concentrated nitric acid is a colourless liquid at room temperature
Fuming nitric acid
A commercial grade of fuming nitric acid contains 98% HNO۳ and has a density of 1.50 g/cm۳. This grade is often used in the explosives industry. It is not as volatile nor as corrosive as the anhydrous acid and has the approximate concentration of 21.4 M
Anhydrous nitric acid
White fuming nitric acid, pure nitric acid or WFNA, is very close to anhydrous nitric acid. It is available as 99.9% nitric acid by assay. One specification for white fuming nitric acid is that it has a maximum of 2% water and a maximum of 0.5% dissolved NO۲ . Anhydrous nitric acid has a density of 1.513 g/cm۳ and has the approximate concentration of 24 molar. Anhydrous nitric acid is a colorless mobile liquid with a density of 1.512 g/cm۳ that solidifies at −۴۲ °C to form white crystals[clarification needed]. As it decomposes to NO۲ and water, it obtains a yellow tint. It boils at 83 °C. It is usually stored in a glass shatterproof amber bottle with twice the volume of head space to allow for pressure build up, but even with those precautions the bottle must be vented monthly to release pressure