Nitric acid

XII CHEMISTRYMS. SIDRA JAVED

NITRIC ACIDNitric acid is a strong mineral acid.

It is a monobasic acid.

It is a strong oxidizing agent and can oxidize metals and nonmetals easily.

It is used in the manufacture of fertilizers, silk industry, explosive materials such as (T.N.T) etc.

INDUSTRIAL PREPARATION OF NITRIC ACID

PRIMARY OXIDATION: OXIDATION OF AMMONIA

Oxidation of ammonia is carried out in a CATALYTIC CHAMBER

Here 1 part of NH3 and 8 parts by volume of O2 are reacted.

The temperature of chamber is about 600oC.

This chamber contains PLATINUM gauze which serves as catalyst.

Oxidation of NH3 is a reversible and exothermic reaction.

4NH3 + 5O2 ⇄ 4NO + 6H2O ΔH =-24.8Kcal/mol

According to Le- chatelier's principle, a decrease in temperature favours the reaction in forward direction.

In primary oxidization 95% of ammonia is converted into nitric oxide (NO).

Nitric oxide (NO) gas obtained by the oxidation of NH3 is very hot.

In order to reduce its temperature, it is passed through a HEAT EXCHANGER where the temperature of NO is reduced to 150oC.

SECONDARY OXIDATION - FORMATION OF NO2

NO after cooling is transferred to another oxidizing tower where at about 50oC it is oxidized to NO2.

2NO + O2⇄ 2NO2

ABSORPTION - FORMATION OF HNO3

NO2 from secondary oxidation chamber is introduced into a ABSORPTION TOWER.

NO2 gas passed through the tower and water is showered over it.

By the absorption, nitric acid (HNO3) is obtained.

3NO2 + H2O → 2HNO3 + NO

REABSORPTION OF HNO3

Nitric acid so obtained is very dilute.

It is recycled in an absorption tower so that more and more NO2 get absorbed.

HNO3 after recycle becomes about 68% concentrated.

END OF LESSON