Difference between revisions of "Nitrous acid"

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'''Nitrous acid''' is a monobasic weak acid, which can only exist in diluted solution and in the salt form (nitrite). It has the chemical formula '''HNO<sub>2</sub>'''.
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'''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 '''HNO<sub>2</sub>'''.
  
 
==Properties==
 
==Properties==
 
===Chemical===
 
===Chemical===
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Free nitrous acid is unstable decomposes to release nitrogen oxides:
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Free nitrous acid is unstable. It decomposes to release nitrogen oxides:
  
 
:2 HNO<sub>2</sub> → NO<sub>2</sub> + NO + H<sub>2</sub>O
 
:2 HNO<sub>2</sub> → NO<sub>2</sub> + NO + H<sub>2</sub>O
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==Preparation==
 
==Preparation==
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Nitrous acid can be prepared by carefully adding a diluted strong acid to a nitrite salt. If the acid is too strong or the addition is too sudden, some of the nitrous acid will rapidly decompose.
+
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 MNO<sub>2</sub> → 3 MX + HNO<sub>2</sub> + NO + NO<sub>2</sub> + H<sub>2</sub>O
 
:3 HX + 3 MNO<sub>2</sub> → 3 MX + HNO<sub>2</sub> + NO + NO<sub>2</sub> + H<sub>2</sub>O
  
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Dissolving [[dinitrogen trioxide]] in cold water will result in very pure nitrous acid:
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Dissolving [[dinitrogen trioxide]] in cold water will result in a solution of pure nitrous acid:
  
 
:N<sub>2</sub>O<sub>3</sub> + H<sub>2</sub>O → 2 HNO<sub>2</sub>  
 
:N<sub>2</sub>O<sub>3</sub> + H<sub>2</sub>O → 2 HNO<sub>2</sub>  
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===Safety===
 
===Safety===
 
Nitrous acid is corrosive and it tends to give off nitrogen oxides, which are irritant and toxic.
 
Nitrous acid is corrosive and it tends to give off nitrogen oxides, which are irritant and toxic.
−
 
−
Nitrous acid explodes in contact with [[phosphorus trichloride]].
 
  
 
===Storage===
 
===Storage===
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Nitrous acid cannot be stored for long periods of time and has to be made in situ.
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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===
 
===Disposal===
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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 relative harmless [[sodium nitrate]].
+
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==
 
==References==
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[[Category:Unstable materials]]
 
[[Category:Unstable materials]]
 
[[Category:Materials unstable in basic solution]]
 
[[Category:Materials unstable in basic solution]]
 +
[[Category:Materials stable only in solution]]
 
[[Category:Corrosive chemicals]]
 
[[Category:Corrosive chemicals]]

Latest revision as of 20:12, 21 April 2019

Nitrous acid
Names
IUPAC name
Nitrous acid
Systematic IUPAC name
Hydroxidooxidonitrogen
Other names
Kyselina dusite
Nitrosyl hydroxide
Identifiers
Jmol-3D images Image
Properties
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
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

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