nitrous acid

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nitrous acid

a weak monobasic acid known only in solution and in the form of nitrite salts. Formula: HNO2
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Nitrous Acid


(HNO2) a monoprotic, unstable, and quite weak acid; it exists only in dilute cold water solutions. Its structural formula is HO—N=0. Its dissociation constant is 4.5 x 10-4 at 18°C. It forms along with nitric acid when N02 is dissolved in water:

2N02 + H20 = HN02 + HN03

Upon heating and the action of strong acids or oxidizers, nitrous acid dissociates with the formation of nitric oxide:

3HN02 = HNO3 + 2NO + H20

The compounds N20, NO, NH2OH, NH3, and others may be obtained by the reduction of nitrous acid. The salts of nitrous acid (nitrates) are obtained by the reduction of nitrates.

The most important property of nitrous acid is its ability to diazotize aromatic amines. For this reason, sodium nitrate (NaN02) is widely used in the production of azo dyes; free nitrous acid is produced upon the action of acids on this salt:

NaN02 + HCl = NaCl + HN02

Nitrous acid and its salts are poisonous if ingested. Poisoning of professionals is rare. Sodium nitrite is used in medicine in cases of cardiac angina and spasms of the vessels of the cerebrum.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.

nitrous acid

[′nī·trəs ′as·əd]
(inorganic chemistry)
HNO2 Aqueous solution of nitrogen trioxide, N2O3.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.