Nitrous acid

Nitrous acid

Names
IUPAC name Nitrous acid
Systematic IUPAC name Hydroxidooxidonitrogen
Other names Kyselina dusite Nitrosyl hydroxide
Identifiers
Jmol-3D images	Image
SMILES O=NO
Properties
Chemical formula	HNO2
Molar mass	47.013 g/mol
Appearance	Pale blueish solution
Density	1-1.1±0.1 g/cm3 (1.1 for maximum possible concentration)
Melting point	Only known in aqueous solution
Boiling point	Only known in aqueous solution
Solubility in water	Miscible
Solubility	Reacts with bases, hydrazoic acid
Acidity (pKa)	3.35
Hazards
Safety data sheet	Guidechem
Related compounds
Related compounds	Nitric acid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Nitrous acid is a monobasic weak acid, which can only exist in dilute aqueous solution. Salts of this acid (nitrites) are stable and if stored properly, they have infinite shelf life. It has the chemical formula HNO₂.

Properties

Chemical

Free nitrous acid is unstable. It decomposes to release nitrogen oxides:

2 HNO₂ → NO₂ + NO + H₂O

The resulting nitrogen dioxide reacts with water to produce nitric acid.

Physical

Nitrous acid can only exist as solution and as such, all of its properties result from the solution, rather than pure compound.

Availability

Nitrous acid is not sold by chemical suppliers due to its instability and must be made in situ.

Preparation

Nitrous acid can be prepared by carefully adding a cold and dilute solution of a strong acid to a nitrite salt. If the acid solution is too concentrated or the addition is too sudden, some of the nitrous acid will rapidly decompose.

3 HX + 3 MNO₂ → 3 MX + HNO₂ + NO + NO₂ + H₂O

Dissolving dinitrogen trioxide in cold water will result in a solution of pure nitrous acid:

N₂O₃ + H₂O → 2 HNO₂

Projects

• Make nitrite salts
• Destroy azides
• Make diazonium salts

Handling

Safety

Nitrous acid is corrosive and it tends to give off nitrogen oxides, which are irritant and toxic.

Storage

Nitrous acid cannot be stored, due to its disproportionation into nitrogen oxides and nitric acid. It is made in situ and is used immediately.

Disposal

Nitrous acid can be neutralized with any base. Sodium percarbonate can also be used, as it will oxidize the nitrous acid to nitric acid and the sodium carbonate will neutralize the said acid to the relatively harmless sodium nitrate.

References

Relevant Sciencemadness threads

• Nitrous acid production & shelf life