Ammonia is a gas with the chemical formula NH3. It is extremely important in the agricultural industry, because it is used to make fertilisers.
Ammonia is made by combining nitrogen and hydrogen. The nitrogen is obtained by fractional distillation of air and the hydrogen is attained by hydrocarbon cracking.
The properties of ammonia
- It is a colourless gas with a strong, choking smell.
- It is very soluble in water.
- It is less dense than air.
- You can test the presence of ammonia by reacting it with hydrogen chloride gas. This forms a white smoke. The smoke is made of tiny particles of solid ammonium chloride:
NH3 (g) + HCl (g) à NH4Cl (s)
- The solution in water is alkaline – it turns red litmus blue.
- Since ammonia solution is alkaline, it reacts with acids to form salts. For example with nitric acid it forms ammonium nitrate:
NH3 (aq) + HNO3 (aq) à NH4NO3 (aq)
The process of manufacturing ammonia
- Nitrogen is made to react with hydrogen in the ratio 1:3, at 4500C temperature and 200 atmospheres pressure.
- Finely divided iron catalyst is also used to speed up the reaction.
- At these conditions, about 15% ammonia of the combined mixture of nitrogen and hydrogen is formed.
- The temperature is lowered and the ammonia is allowed to condense.
- Liquid ammonia forms.
- The unreacted gasses are recycled until all of the gaseous mixture has been converted into ammonia.
Improving the yield of ammonia
- As said before, ammonia is formed when nitrogen and hydrogen gases are mixed. The chemical equation for this reaction is as follows:
- You can see that the reaction is reversible and it can reach a position of equilibrium.
- The position of equilibrium can be shifted to the right hand side to give a high yield of ammonia, by using a low temperature and high pressure.
- However, the reaction is quite slow at a lower temperature and hence, a compromise of 4500C is used.
- Moreover, carrying out the reaction at a very high pressure is expensive and hence, a cost effective pressure of 200 atmospheres is used,
Uses of ammonia
- Ammonia is used in the manufacture of fertilizers such as ammonium nitrate.
- It is used in manufacturing nitric acid.
- Ammonia is also used in manufacturing the synthetic polymer- nylon.
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