Description
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
solution:
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”.
Physical properties
Pale blue solution; stable only in solution; weak acid, Ka 4.5x10-4.
Definition
A weak
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
sulfide.
Definition
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.
Preparation
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.
Hazard
Rapidly forms nitric oxide and nitric acid in water; [Merck Index] A strong oxidizer; Causes burns; Highly toxic by ingestion and inhalation.
