Nitric acid

Nitric acid (HNO3), also known as aqua fortis (Latin for 'strong water') and spirit of niter, is a highly corrosive mineral acid. 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% HNO3, it is referred to as fuming nitric acid. Depending on the amount of nitrogen dioxide present, fuming nitric acid is further characterized as white fuming nitric acid at concentrations above 95%, or red fuming nitric acid at concentrations above 86%. Nitric acid is the primary reagent used for nitration – the addition of a nitro group, typically to an organic molecule. While some resulting nitro compounds are shock- and thermally-sensitive explosives, a few are stable enough to be used in munitions and demolition, while others are still more stable and used as pigments in inks and dyes. Nitric acid is also commonly used as a strong oxidizing agent. Commercially available nitric acid is an azeotrope with water at a concentration of 68% HNO3, which is the ordinary concentrated nitric acid of commerce. This solution has a boiling temperature of 120.5 °C at 1 atm. Two solid hydrates are known; the monohydrate (HNO3·H2O or NO3) and the trihydrate (HNO3·3H2O). Nitric acid of commercial interest usually consists of the maximum boiling azeotrope of nitric acid and water, which is approximately 68% HNO3, (approx. 15 molar). The density of concentrated nitric acid is 1.40 g/cm3 (68% conc). This is considered concentrated or technical grade, while reagent grades are specified at 70% HNO3. An older density scale is occasionally seen, with concentrated nitric acid specified as 42° Baumé. Nitric acid is subject to thermal or light decomposition and for this reason it was often stored in brown glass bottles: