Nitric acid (HNO3)
is a colourless, highly corrosive, poisonous liquid that gives off choking red
or yellow fumes in moist air. It is miscible with water in all proportions.
Nitric acid of commerce is typically a solution of 52% to 68% nitric acid in
water. Solutions containing over 86% nitric acid are commonly called fuming
nitric acid. White fuming nitric acid (WFNA) is similar to the anhydrous
variety, and red fuming nitric acid (RFNA) has a reddish brown colour from
dissolved nitrogen oxides. When treated with hydrogen fluoride, both varieties
form inhibited fuming nitric acid, which has increased corrosion resistance in
Nitric acid is made by
reaction of nitrogen dioxide (NO2) with water.
3 NO2 + H2O
à 2 HNO3 + NO
Normally, the oxygen in air to
produce additional nitrogen dioxide re-oxidizes the nitric oxide produced by
the reaction. Bubbling nitrogen dioxide through hydrogen peroxide can help to
improve acid yield.
2 NO2 + H2O2
à 2 HNO3
Nitric acid is mainly used in
the production of fertilizers. Nitric acid is neutralized with ammonia to
give ammonium nitrate.
Nitric acid can be used to
manufacture components of trinitrotoluene (TNT) and also the ubiquitous and
so-called plastic explosive â€œSemtexâ€. It can be used as an oxidizing agent in
the production of some solid fuels for rocket propulsion;
As an ageing agent in
woodworking where it can be used in very dilute forms (typically below 10%) to
change the appearance of some woods and to produce a colour similar to that of
oiled or waxed surfaces old.
Higher concentration nitric
acid is used for some specialist applications like metallurgy, and is generally
produced by concentrating weak acid rather than by producing it directly.