Nitrous acid,HN02, is the aqueous solution of nitrogen trioxide. It is a moderately strong and rapid oxidizing agent used for diazotization.
Nitrous acid is a diazotizing agent. The acid diazotizes primary aromatic amines to diazo derivatives in manufacturing azo dyes.
Nitrous acid is unstable. It decomposes to form nitric acid and nitric oxide:
3HNO2 → NO3¯ + H3O+ + 2NO
Strong oxidizing agents, such as permanganate, readily oxidize nitrous acid to nitric acid.
Nitrous acid is an effective oxidizing agent. It oxidizes hydrogen sulfide to sulfur forming either nitric oxide or ammonia, depending on the acidity of the solution:
2HNO2 + H2S → S + 2NO + 2H2O
HNO2 + 3H2S → 3S + NH3 + 2H2O
In acid medium it oxidizes iodide ion to iodine:
HNO2 + I¯ + 6H+ → 3I2 + NH3 + 2H2O
Nitrous acid (molecular formula?HNO2) is a weak
and monobasic acid known only in solution and in the
form of nitrite salts. Nitrous acid rapidly decomposes
into nitrogen oxide, nitric oxide and water when in
2HNO2 ? NO2 + NO+H2O
It can also decompose into nitric acid and nitrous
oxide and water.
4HNO2 ? 2HNO3 +N2O +H2O
Nitric acid (HNO3), also known as “aqua fortis”
and “spirit of nitre”, is a highly corrosive and toxic
strong acid that can cause severe burns. It is colorless
when pure and a slight yellow when “glacial”. Older
samples tend to acquire a yellow cast due to the accumulation
of various oxides of nitrogen. If the solution contains more than 86% nitric acid, it is referred to as
“fuming nitric acid”.
A weak acid occurring only in the form
of a light-blue solution.
Pale blue solution; stable only in solution; weak acid, Ka 4.5x10-4.
Formation of diazotizing compounds by reaction with primary aromatic amines, source of nitric
Nitrous acid is a nitrogen oxoacid. It is a conjugate acid of a nitrite. It (as sodium nitrite) is used as part of an intravenous mixture with sodium thiosulfate to treat cyanide poisoning. There is also research to investigate its applicability towards treatments for heart attacks, brain aneurysms, pulmonary hypertension in infants, and Pseudomonas aeruginosa infections.
Nitrous acid may be obtained in solution by adding a strong acid to nitrite; e.g., adding hydrochloric acid to sodium nitrite solution: H+ + NO2 ˉ → HNO2.
acid known only in solution, obtained by
acidifying a solution of a nitrite. It readily
decomposes on warming or shaking to nitrogen
monoxide and nitric acid. The use
of nitrous acid is very important in the
dyestuffs industry in the diazo reaction: nitrous
acid is liberated by acidifying a solution
of a nitrite (usually sodium nitrite) in the presence of the compound to be diazotized.
Nitrous acid and the nitrites are normally
reducing agents but in certain
circumstances they can behave as oxidizing
agents, e.g. with sulfur dioxide and hydrogen
nitrous acid: A weak acid, HNO2,known only in solution and in thegas phase.It is prepared by the actionof acids upon nitrites, preferablyusing a combination that removesthe salt as an insoluble precipitate(e.g.Ba(NO2)2 and H2SO4). The solutionsare unstable and decompose on heating to give nitric acid and nitrogenmonoxide.Nitrous acid can functionboth as an oxidizing agent(forms NO) with I– and Fe2+, or as areducing agent (forms NO3-) with,forexample, Cu2+; the latter is mostcommon.It is widely used (preparedin situ) for the preparation of diazoniumcompounds in organic chemistry.The full systematic name isdioxonitric(III) acid.
Rapidly forms nitric oxide and nitric acid in water; [Merck Index] A strong oxidizer; Causes burns; Highly toxic by ingestion and inhalation.
Mutation data reported.
Flammable by chemical reaction; a powerful oxidizer. Explodes on contact with
phosphorus trichloride. Reacts violently
with PH3 and Pcb. Reactions with l-amino-
decahydroborate(2-), hydrazine (product is
hydrogen azide) may give explosive
products. Incompatible with anilines (e.g., 4-
bromoahe , 2-chloroaniline, 3-
chloroaniline, 2-nitroadine, 3-nitroaniline,
4-nitroaniline, aniline ), semicarbazone, silver
nitrate. When heated to decomposition it
emits hghly toxic fumes of NOx. See also