NITRIC ACID ( HNO3)
 
 
 
INTRODUCTION
 
    Nitric acid is a strong mineral acid. It is a mono-basic 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
 
    On industrial scale, nitric acid can be prepared by the following methods.
    (a) CHILLI-SALT PETER's METHOD: By NaNO3
    (b) BRIKLAND-EYDE's METHOD: By using air
    (c) OSTWALD' s METHOD : By ammonia
OSTWALD'S METHOD
 
    Materials used:
     Ammonia gas
     Water
     Oxygen gas
CATALYST
 
    Platinum
DETAILS OF PROCESS
 
    First step
PRIMARY OXIDATION
(formation of nitric acid)
    Oxidation of ammonia is carried out in a catalyst chamber in which one part of ammonia and eight parts     of oxygen by volume are introduced. The temperature of chamber is about 600oC. This chamber contain     a platinum gauze which serves as catalyst.
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CHEMISTRY OF
PRIMARY OXIDATION
    Oxidization of ammonia is reversible and exothermic process. Therefore according to Le- chatelier's     principle.,a decrease in temperature favour reaction in forward direction. In primary oxidization 95% of     ammonia is converted into nitric oxide (NO).
    Second step
SECONDARY OXIDATION
(formation of nitrogen dioxide)
    Nitric oxide gas obtain by the oxidation of ammonia is very hot. In order to reduce its temperature , it is     passed through a heat exchanger where the temperature of nitric oxide is reduce to 150oC. Nitric oxide     after cooling is transferred to another oxidizing tower where at about 50o c it is oxidizing to NO2.
    Third step
ABSORPTION OF NO2
(formation of HNO3)
    Nitrogen dioxide from secondary oxidation chamber is introduced into a special absorption tower.
     NO2 gas passed through the tower and water is showered over it. By the absorption, nitric acid is     obtained.
3 NO2 + H2O 2HNO3 + NO
    Nitric acid so obtain is very dilute. It is recycled in absorption tower so that more and more NO2 get     absorbed. HNO3 after recycle becomes about 68% concentrated.
    Fourth step
CONCENTRATION
    In order to increase the concentrated of HNO3 , vapour of HNO3 are passed over concentrated H2SO4.     Being a dehydrating agent H2SO4,absorbs water from HNO3 and concentrated HNO3 is obtained.
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