Aims Explain the conditions in which NO 2 can be formed Describe the Ostwald process
Nitric Acid Nitrogen is a very unreactive gas. Nitric acid (HNO 3 ) is formed when nitrogen dioxide (NO 2 ), in the presence of air, dissolves in water. The presence of nitrogen oxides in the air, mean that they will dissolve in rain to produce a mildly acidic solution. This has the result that: – nitrogen compounds are added to the soil. – the acidity of the soil will be increased.
Nitrogen dioxide is produced by the passage of a high voltage spark through air since a large amount of energy is required to break the bonds between the nitrogen atoms in the molecules. These conditions occur when: – lightning passes through air – a spark passes in the spark plug of a car engine This does not provide an economic way of making nitrogen dioxide.
Nitric Acid Ammonia normally reacts with oxygen to give nitrogen and water. The combination of nitrogen and oxygen does not provide an economic industrial route to nitric acid. The catalytic oxidation of ammonia to form nitrogen dioxide is a step in the industrial manufacture of nitric acid OSTWALD PROCESS. The catalytic oxidation of ammonia can be carried out in the laboratory.
The Ostwald Process Ammonia Oxygen Water Nitric acid Reaction Chamber (Pt catalyst) 600-900 o C Nitrogen monoxide Nitrogen dioxide Oxygen
This process is carried out at a moderately high temperature to allow it to proceed fairly quickly. A platinum catalyst is used. Since the reaction is exothermic it is not necessary to continue heating it after the reaction has started since it will supply sufficient energy to continue at a reasonable rate.