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Fertilisers

How is Nitric Acid Made?

Nitric acid is made from the reaction of ammonia with oxygen.

The first stage produces nitrogen monoxide.
(The same gas is formed as a pollutant in petrol engines).

A hot platinum catalyst is used (about 850 °C).
The reaction is highly exothermic and the heat given out by
the reaction is sufficient to keep the reaction going.

ammonia + oxygen    nitrogen monoxide  + water.
4NH_3(g)  +  5O_2(g)               4NO_(g)     +    6H₂O_(g)

The second stage involves the reaction of
nitrogen monoxide with more oxygen.

nitrogen monoxide + oxygen     nitrogen dioxide.
2NO_(g)         +         O_2(g)               2NO_2(g)

Finally, nitrogen dioxide reacts with water and more oxygen.

nitrogen dioxide  +  oxygen   +   water      nitric acid.
4NO_2(g)          +          O_2(g)  +  2H₂O_(l)     4HNO_3(aq)

The overall reaction is

ammonia  +  oxygen        nitric acid     +    water.
4NH_3(g)    +   8O_2(g)           4HNO_3(aq)    +  4H₂O_(l)

This is the oxidation of ammonia to produce nitric acid.

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