Ammonia and Its Uses

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AMMONIA

Ammonia, NH3, is an important raw material in the manufacture of fertilizers. Some ammonia is converted into nitric acid which itself is used in the manufacture of fertilizers and explosives. Ammonia is also a useful ingredient in some cleaning fluids.

Ammonia is a vital route by which nitrogen in the air can be made available to plants to enable them to build protein molecules. Plants cannot use nitrogen directly from the air. They need nitrogen compounds, dissolved in water, which they absorb through their roots.

Without synthetic, ammonia-based fertilizers, the world would be unable to grow enough food to feed its population.

The Haber process

The raw materials for the process of making ammonia are hydrogen and nitrogen.

Hydrogen is obtained by reacting natural gas (mostly methane) with steam, or from cracking oil fractions.

Nitrogen is obtained from the air. Air is 78 per cent nitrogen and nearly all the rest is oxygen. When hydrogen is burned in air, the oxygen combines with the hydrogen - leaving nitrogen behind.

In the Haber process, nitrogen and hydrogen react together under these conditions:

a high temperature - about 450°C

a high pressure - about 200 atmospheres (200 times normal pressure)

an iron catalyst

In addition, any unreacted nitrogen and hydrogen are recycled. The reaction is reversible. In a chemical equation, the symbol is used instead of an ordinary arrow if the reaction is reversible:

This equation summarizes the Haber process:

3H2 + N2 = 2NH3 ( It's a reversible reaction )

Uses of ammonia A major use of ammonia is in the manufacture of fertilisers. Some ammonia is first converted into nitric acid, HNO3.

Production of nitric acid from ammonia

Ammonia, NH3, is oxidised in the presence of a platinum/rhodium catalyst to form nitrogen monoxide:

4NH3 + 5O2 → 4NO + 6H2O

The nitrogen monoxide is then further oxidised to form nitrogen dioxide:

2NO + O2 → 2NO2

The nitrogen dioxide is then dissolved into water in the presence of oxygen to form concentrated nitric acid:

4NO2 + 2H2O + O2 → 4HNO3

Production of fertilisers The most effective fertilisers contain nitrogen because plants need it in order to produce proteins. Phosphorus and potassium are also essential elements commonly found in fertilisers.

Many fertilisers are ammonium salts. They can also be made from ammonium hydroxide (ammonia solution). If ammonium hydroxide is used, water is also produced in the neutralisation reaction.

Ammonium Sulphate (NH4)2SO4

Ammonium Nitrate NH4NO3

Urea NH2CONH2