Nitrous acid. Chemical and physical properties

Nitrous acid is a monobasic weakacid, which can exist only in dilute aqueous solutions of blue and in gas form. The salts of this acid are called nitrite or nitrite. They are toxic and more resistant than acid itself. The chemical formula of this substance is as follows: HNO2.

Physical properties:
1. The molar mass is 47 g / mol.
2. The relative molecular weight is 27 amu.
3. The density is 1.6.
4. The melting point is 42 degrees.
5. The boiling point is 158 degrees.

Chemical properties of nitrous acid

1. If the solution with nitrous acid is heated, the following chemical reaction will occur:
3HNO2 (nitrous acid) = HNO3 (nitric acid) + 2NO (nitrogen oxide, released as gas) + H2O (water)

2. In aqueous solutions, it dissociates and is easily displaced from the salts by stronger acids:
H2SO4 (sulfuric acid) + 2NaNO2 (sodium nitrite) = Na2SO4 (sodium sulfate) + 2HNO2 (nitrous acid)

3. The substance considered by us can exhibit both oxidizing and reducing properties. When exposed to stronger oxidants (eg chlorine, hydrogen peroxide H2O2, potassium permanganate), it oxidizes to nitric acid (in some cases, the formation of a nitric acid salt):

Reducing properties:

HNO2 (nitrous acid) + H2O2 (hydrogen peroxide) = HNO3 (nitric acid) + H2O (water)
HNO2 + Cl2 (chlorine) + H2O (water) = HNO3 (nitric acid) + 2HCl (hydrochloric acid)
5HNO2 (nitrous acid) + 2HMnO4 = 2Mn (NO3) 2 (manganese nitrate, nitric acid salt) + HNO3 (nitric acid) + 3H2O (water)

Oxidizing properties:

2HNO2 (nitrous acid) + 2HI = 2NO (oxygen oxide, as gas) + I2 (iodine) + 2H2O (water)

Production of nitrous acid

This substance can be obtained in several ways:

1. When nitrogen (III) is dissolved in water:

N2O3 (nitric oxide) + H2O (water) = 2HNO3 (nitrous acid)

2. When the nitrogen of the oxide (IV) is dissolved in water:
2NO3 (nitric oxide) + H2O (water) = HNO3 (nitric acid) + HNO2 (nitrous acid)

Application of nitrous acid:
- diazotization of aromatic primary amines;
- production of diazonium salts;
- in the synthesis of organic substances (for example, for the production of organic dyes).

The effect of nitrous acid on the body

This substance is toxic, has a bright mutagenic effect, since in essence it is a deaminating agent.

What are nitrites

Nitrites are various salts of nitrous acid. To the effect of temperatures, they are less stable than nitrates. Required for the production of certain dyes. Are applied in medicine.

Particular importance has acquired for a person nitritesodium. This substance has the formula NaNO2. Used as a preservative in the food industry for the production of fish and meat products. It is a powder of pure white or slightly yellowish color. Sodium nitrite is hygroscopic (except for purified sodium nitrite) and readily soluble in H2O (water). In the air it can gradually oxidize to sodium nitrate, has strong reducing properties.

Sodium nitrite is used in:
- chemical synthesis: to produce diazoamine compounds, to deactivate excess sodium azide, to produce oxygen, sodium oxide and sodium nitrogen, to absorb carbon dioxide;
- in the production of food products (food additive E250): as an antioxidant and antibacterial agent;
- in construction: as antifreeze additive to concrete in the manufacture of structures and building products, in the synthesis of organic substances, as a corrosion inhibitor of the atmospheric, in the production of rubbers, poppers, mortar additives for explosives; when processing metal to remove the tin layer and during phosphating;
- in photography: as an antioxidant and reagent;
- in biology and medicine: vasodilator, spasmolytic, laxative, bronchodilator; as an antidote for the poisoning of an animal or human with cyanides.

At present, other salts of nitrous acid are also used (for example, potassium nitrite).