Nitric Acid

Nitric acid is a colorless to pale yellow liquid with a characteristic acidic (corrosive) and suffocating odour. Nitric acids easily decompose in the presence of light, producing nitrogen dioxide (NO₂), which itself is a brownish gas. The yellowish color commonly found in nitric acid is caused by the presence of small amounts of nitrogen dioxide. Nitric acid is one of the strongest known oxidants and it will corrode almost all metals except gold and platinum.
Nitric acid is a strong oxidant. Nitric acid will violently oxidize non-metals, metals, inorganic and organic compounds. Nitric acid itself is reduced to generate various reduction products, such as NO, NO₂, N₂O, etc. These products depend on acid concentration and reaction temperature.

What is Nitric Acid?

Early chemists knew about the preparation and application of nitric acid. An ordinary laboratory mechanism used for many years is to heat potassium nitrate with concentrated sulphuric acid. In 1776, Lavoisier proved that it consist oxygen, and later on Joseph-Louis Gay-Lussac and Claude-Louis Berthollet determined its chemical composition. The main method of making nitric acid is the catalytic oxidation of ammonia. In a method developed by Ostwald, ammonia is oxidized to nitric oxide and nitrogen dioxide in sequence by air or oxygen in the presence of a platinum mesh catalyst. Nitrogen dioxide is absorbed by water to form nitric acid. The outcome acidic aqueous solution (about 50-70 weight percent acid) can be dehydrated by distillation with sulfuric acid. Nitric acid decomposes into water, nitrogen dioxide and oxygen, forming a brownish-yellow solution. It is a strong acid that fully ionises in aqueous solution to hydronium (H₃O⁺) and nitrate (NO₃^–) ions, and is a strong oxidant (reagent that acts as an electron acceptor in redox reactions).

Preparation of Concentrated Nitric Acid:

A mechanism for the production of conc. HNO₃ consists the reaction between the liquid NO₂ and water (or dil. HNO₃) within the presence of O2 at 50 ATP and a temperature of 75°C. the outcome is 88%  HNO₃. 4NO₂+ O₂+ 2H₂O—— 4HNO₃

Preparation of Fuming Nitric Acid:

It is made by Conc. HNO₃ contains a small amount of starch. The starch reduces some of the acid to NO₃, which dissolves in the remaining acid to produce fuming nitric acid. This acid is yellow due to the presence of dissolved oxides of highly corrosive liquid nitrogen consisting of HNO₃. Fuming nitric acid can be a stronger oxidizing and nitrating agent than concentrated nitric acid.

Physical Properties:

Some of the physical properties of acids are:

• Generally, acids have a sour taste.
• Acid makes blue litmus paper red.
• The acid turns methyl orange into red.
• Usually, acids are neutral to phenolphthalein.

Chemical Properties:

• Oxidizing: Nitric acid is certainly a strong oxidant due to the convenience with which it decomposes to present nascent oxygen.

2HNO₃→ 2NO₂+ H₂O + O NO₂ gas is produced and this gas continues to dissolve, the colour of the acid -yellow or maybe reddish yellow in higher concentrations.

• Non−metals:  Non−metals like sulphur, carbon, phosphorus and iodine are oxidised to their congruence oxy−acids. for instance,

Sulphur is oxidized to sulphuric acid- S + 6HNO₃→ H₂SO4</sub.+ 6NO₂+ 2H₂O Carbon is oxidized to carbonic acid- C + 4HNO₃→ H₂CO₃ + 4NO₂ + H₂O

• Metalloids: Metalloids such as arsenic and antimony are oxidized to the congruence oxy−acids. e.g., arsenic is oxidized to ortho−arsenic acid (H₃AsO₄).

As + 5HNO₃→ H3AsO₄ + 5NO₂ + H₂O

• Metals: Mostly all metals (not necessarily all), except noble metals like gold and platinum are attacked by nitric acid. Some of them make nitrates and others such as tin and antimony give oxides. During the reaction, a part of the acid is reduced to offer products like NO₂, NO, N₂, N₂O, NH₂OH or NH3and the character of products depends upon the concentration of the acid, temperature and therefore the nature of the metal.

M + HNO₃→ MNO₃ + H

Uses

• Basic calcium nitrate is utilised as a fertiliser. Silver nitrate is utilised in photography and sodium nitrate within the manufacture of gunpowder and fireworks.
• Explosives like dynamite, nitroglycerine, trinitrotoluene (TNT), picric acid etc, it’s used for the manufacturing process.
• In the manufacturing process of artificial silk, medicines, dyes, and perfumes.
• In the purification of gold and silver.
• As a crucial reagent within the laboratory.
• In the manufacture of H₂SO₄
• Also in the etching designs on wares of brass, bronze, etc.
• In the preparation of aqua regia.

Conclusion

Nitric acid (HNO₃) is a colourless liquid acid largely used in the manufacture of explosives and fertilizers. When dissolved in water, nitric acid molecules separate (or dissociate) into hydrogen ions (H⁺) and nitrate ions (NO₃^–). The fact that almost all nitric acid molecules dissociate, makes nitric acid a strong acid. Nitric acid is the raw material for the industrial production of nitrate fertilizers. Nitrogen makes oxyacids such as hypnotic acid, nitrous acid, per nitric acid and nitric acid. Among them, nitric acid is an industrially important oxo acid. Nitric acid is obtained by the reaction of ammonia with oxygen. The nitric acid can then be used to make a ample of compounds. This mechanism can produce large quantities of fertiliser at a relatively low cost.