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Uses of Nitric Acid

We know that acids are those compounds which tend to give hydrogen ions in their respective solutions. There are mainly two types of acids; mineral acids or inorganic acids and organic acids. Mineral acids or inorganic acids are usually extracted from minerals and consist of non-metals such as sulphuric acid, nitric acid, hydrochloric acid etc. Organic acids consist of carbon atoms such as acetic acid, formic acid etc. In this article we will discuss about nitric acid which is one of the most common inorganic acid used for various applications.

Nitric acid is also known as aqua fortis or spirit of niter. It is a colourless liquid with highly corrosive nature.  It decomposes partially in the presence of air to form oxides of nitrogen with water which turns the solution pale yellow in colour. In market, nitric acid is usually available with concentration of 68% in water. More concentrated solution that is 86 % of nitric acid is marketed as fuming nitric acid. Nitric acid is one of the common reagents for nitration of organic compounds for the addition of nitro group in organic compounds. Nitric acid is also a good oxidizing agent and is used for manufacturing of other inorganic compounds.

The formula of nitric acid is HNO3 in which one hydrogen atom, one nitrogen atom and three oxygen atoms are bonded with each other. It is a planar molecule and exhibits two resonance forms.

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Uses of Nitric Acid in Fertilizers

Nitric acid is key component for the manufacturing of fertilizers especially nitrogenous fertilizers such as ammonium nitrate. The reaction of nitric acid with ammonia forms ammonium nitrate. Nitric acid also involves in the production of other nitrogenous fertilizers such as urea. The mixture of nitric acid with sulphuric acid forms nitrating mixture which is one of the best reagents for nitration reactions. Here sulphuric acid acts as dehydrating agent and will remove water from the nitric acid to continue the reaction in forward direction. The presence of concentrated sulphuric acid removes the azeotrope which is a constant boiling mixture at 68.5% $HNO_{3}$ and produces a vapour with 99% $HNO_{3}$ along with some nitrogen dioxide and oxygen.

Uses of Nitric Acid in Industry

Nitric acid is key component for the manufacturing of many other chemicals and fertilizers. Many polymers such as polyamides, polyurethane are manufactured from nitric acid. Nitric acid is also used in aerospace engineering as rocket propellants. There are different types of propellants which are used in rockets. For example a liquid oxidizer is combined with fuel in liquid-fueled rockets. Since nitric acid is a strong oxidizing agent therefore it has been used as the oxidizer in liquid-fueled rockets. White fuming nitric acid (WFNA) is mainly used as rocket propellant. It is a storable oxidizer which consists of highly concentrated nitric acid (95%) with red fuming nitric acid (RFNA) which is again a storable oxidizer with a nitric acid (84% concentrated). It is also used as precursor for manufacturing of organic nitrogen-containing compounds like nylon.

Common Uses of Nitric Acid

Nitric acid is the most important and useful oxyacid of nitrogen with molecular formula; HNO3 and molar mass 63.01 g mol-1.  It is a colorless fuming liquid with a pungent odor in pure form whereas impure acid turns to yellow color because of presence of dissolved oxides of nitrogen such as $NO_{2}$. Nitric acid is soluble in water and forms azotrop of constant boiling mixture with water with 68% of nitric acid. It is little heavier than water with density of 1.54 g/mL. The boiling point of anhydrous nitric acid is 355.6 K and freezing point is 231.4 K. It is a corrosive mineral acid which causes yellow blisters on skin.

Let’s discuss some common uses of nitric acid. Nitric acid is precursor of many organic and inorganic compounds. For example; nitric acid is used for the manufacturing of explosives such as trinitrotoluene (T.N.T.), nitro glycerine, Gun cotton, Ammonal etc. Many fertilizers like calcium nitrate, ammonium nitrate are also manufactured with the help of nitric acid. It is also useful in manufacturing of other nitrates such as calcium nitrate, silver nitrate, ammonium nitrate etc. Nitric acid plays an important role in preparation dyes, perfumes, drugs etc. from coal tar products. It is also a part of lead chamber process in the manufacturing of sulphuric acid and is used for the purification of some Nobel metals such as silver, gold, platinum etc. $HNO_{3}$ is used in etching designs on metals and alloys like Cu, brass, bronze ware etc. It is a key component of "aqua regia" which is used to dissolve the noble elements and also used as laboratory reagent.

Some other uses are featured below.