Nitrous acid is a monobasic weak acid that can exist only in dilute blue aqueous solutions and in gas form. Salts of this acid are called nitrous acid or nitrite. They are toxic and more stable than the 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 (nitric oxide, liberated as gas) + H2O (water)
2. In aqueous solutions, it dissociates and is easily displaced from salts by stronger acids:
H2SO4 (sulfuric acid) + 2NaNO2 (sodium nitrite) = Na2SO4 (sodium sulfate) + 2HNO2 (nitrous acid)
3. The substance under consideration can exhibit both oxidizing and reducing properties. When exposed to stronger oxidizing agents (for example: chlorine, hydrogen peroxide H2O2, potassium permanganate) is oxidized to nitric acid (in some cases, the formation of a salt of nitric acid):
Recovery 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, in the form of gas) + I2 (iodine) + 2H2O (water)
Getting nitrous acid
This substance can be obtained in several ways:
1. When dissolving nitrogen oxide (III) in water:
N2O3 (nitric oxide) + H2O (water) = 2HNO3 (nitrous acid)
2. When dissolving nitrogen oxide (IV) in water:
2NO3 (nitric oxide) + H2O (water) = HNO3 (nitric acid) + HNO2 (nitrous acid)
The use 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 it is essentially a deaminating agent.
What is nitrite
Nitrites are various salts of nitrous acid. They are less resistant to temperatures than nitrates. Necessary in the production of some dyes. They are used in medicine.
Of particular importance for man has been sodium nitrite. This substance has the formula NaNO2. It is used as a preservative in the food industry in the production of fish and meat products. It is a powder of pure white or slightly yellowish color. Sodium nitrite is hygroscopic (with the exception of purified sodium nitrite) and is highly soluble in H2O (water). In air, it is able to gradually oxidize to sodium nitrate, has strong reducing properties.
Sodium nitrite is used in:
- chemical synthesis: to obtain diazo-amine compounds, to deactivate excess sodium azide, to produce oxygen, sodium oxide and sodium nitrogen, to absorb carbon dioxide;
- in food production (food supplement E250): as an antioxidant and antibacterial agent;
- in construction: as an antifrosty additive to concrete in the manufacture of structures and building products, in the synthesis of organic substances, in the role of an atmospheric corrosion inhibitor, in the production of rubbers, poppers, and an additive solution 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, antispasmodic, laxative, bronchodilator; as an antidote for poisoning an animal or person with cyanides.
Other nitrous acid salts (e.g., potassium nitrite) are also currently used.