Nitrous Acid - HNO2

What is Nitrous Acid?

Nitrous acid is unstable and weakly acidic compound. It is an oxoacid of nitrogen. It is obtained by acidification of nitrite salt with mineral acid. Nitrous acid is a mixture of nitric acid and nitrous gas but with a smaller proportion of oxygen than what exists in nitric acid. Nitrous acid was discovered by Scheele. It is obtained by distilling perfectly dry nitrate of lead in a retort, fitted with a receiver. The liquid comes over which is nitrous acid.

HNO2 Nitrous Acid
Density 1 g/cm³
Molecular Weight/ Molar Mass 47.013 g/mol
Boiling Point 158 °C
Compound Formula HNO2

Nitrous Acid Structure – HNO2

Nitrous Acid

Physical Properties of Nitrous Acid – HNO2

Odour Unpleasantly bitter or pungent
Appearance Pale blue solution
Specific Density 1.35 g/cm3
Systematic name‎ ‎Dioxonitric(III) acid

Chemical Properties of Nitrous Acid – HNO2

  • It is strongly acidic, extremely volatile and rises in thick fumes; boils at a low temperature of 82oC and the specific gravity is 1.45
  • In vapour state, nitrous acid remains unchanged by the action of heat. Gaseous nitrous acid, which is rarely encountered, decomposes into nitrogen dioxide, nitric oxide, and water.
  • Nitrous acid in its fuming state is totally irrespirable but supports the combustion of phosphorus or charcoal when these are introduced into it in a state of combustion.

Uses of Nitrous Acid – HNO2

  • Used in the preparation of diazonium salts from amines and in the preparation of azo dyes in Sandmeyer reaction.
  • Used to remove the toxic nature of potentially explosive compound sodium azide.
  • Nitrous acid is also used as an oxidizer in liquid fuel rockets.

Frequently Asked Questions

What are the uses of nitrous acid?

In industry, nitrous acid has many applications. One important application of this compound is its use in the preparation of diazonium salts which then react to form azo-colouring with aromatic amines and phenols.

Is nitrous acid a strong or weak acid?

Nitrous acid is a weak acid. Nitric acid, on the other hand, is a strong acid. This can be explained by the fact that the conjugate base of nitric acid is much more stable than the conjugate base of nitrous acid.

Why is nitrous acid unstable?

Nitrous acid breaks down into nitric oxide (chemical formula: NO) and nitric acid (chemical formula: HNO3). It may react as either an oxidizing or a reducing agent: in reactions with other substances, the nitrogen atom can either gain or lose electrons.

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