Ammonia and fertilisers: C2 Additional science WJEC

Outlines of

  • The Haber process
  • Production of fertilisers
  • Eutrophication
  • Testing for Ammonia

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AMMONIA AND FERTILISERS
Making Ammonia- The Haber Process
Ammonia (NH) is an industrially important chemical, most often used to make fertilisers. The process
we use to make ammonia was developed by Fritz Haber, and is termed the Haber process.
The raw materials used are...
Nitrogen, which is obtained from the air.
Hydrogen, which is obtained from natural gas.
The Equations for this method of production are...
Nitrogen + Hydrogen Ammonia
The conditions in which the reaction takes place are chosen specifically to ensure maximum yield in
the fastest and most economical fashion. You need to know the conditions used and why they are
chosen.
Temperature: Although the optimum yield of this reaction is given by a low temperature, this makes
the rate of reaction too slow, so although it means a lower yield, a higher temperature is used-
around 450 C.
Pressure: A high pressure would increase the rate of reaction, but it is expensive and poses the risk
of explosion (the hydrogen), so a pressure of 200atm is used.
Catalyst: Adding a catalyst is effective as it increases the rate of reaction without affecting the
yield. An Iron catalyst is used.
NOTE: The reaction is not 100% effective, so to be economical, any unused nitrogen or hydrogen is
recycled and goes through the process again

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Ammonia in Fertilisers
In its natural form, Ammonia is a pungent alkaline gas. It is soluble, and dissolves in water to
form an alkali. It cannot be used as a fertiliser in this form, and so is neutralised with an acid.
(Remember- Acid + Alkali Salt + Water)
This is done in two main ways:
Either
Some Ammonia is converted into nitric acid and used to neutralise the ammonia,
forming ammonium nitrate.…read more

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Testing for Ammonia
You may be asked to identify whether a salt contains ammonia, or just how to identify the gas. If it
is the latter, just use the last step of the outlined test.
Apparatus:
Salt
Sodium hydroxide
Test tube
Pipette
Damp red litmus paper
Put a spatula of salt into your test tube
Add a few drops of sodium hydroxide
Hold damp red litmus paper over the test tube.
If the salt is an ammonium one, it will be producing ammonia.…read more

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