Download Topic 14 Fertilisers

TOPIC 14
Fertilisers
Growth of Plants
 To grow well plants require elements in the
form of water soluble compounds; these are
called NUTRIENTS.
 The most important Nutrients (essential
elements) that plants require are Nitrogen,
Phosphorus and Potassium (NPK)
 These Nutrients are often added in the form
of FERTILISERS
Nitrogen Fixing
 Some plants can absorb Nitrogen directly from the
air.Plants that can do this e.g.Peas, beans and
clover are called Leguminous plants. They contain
tiny nodules called Nitrifying Bacteria.
 Most plants can’t do this and require to absorb
Nitrogen in the form of Nitrogen compounds.
 Nitrogen in the form of compounds is called Fixed
Nitrogen
The Industrial Preparation of
Ammonia-The Haber Process
N2(g)+3H2(g)
2NH3(g)(Ammonia)
This an example of a Reversible Reaction
(a reaction that goes both ways)
To obtain the best yield of Ammonia the reaction requires a
Catalyst of Fe, a Temp of 500C and a pressure of 150-300 atms.
Starting Materials: Nitrogen is obtained by the fractional
distillation of the Air and the Hydrogen is obtained from CH4 in
Natural Gas
Industrial Preparation of Nitric
Acid-The Ostwald Process
Takes place in 3 stages; with the first one being the most
difficult
 1. NH3(g) + O2(g)
NO(g) + H20
 2. NO(g) + O2(g)
NO2(g)
3.. NO2 + H2O
HNO3 (Nitric Acid).
An Platinum Catalyst and a temp 5000C are required to make
the first stage happen.
After the reaction has started the platinum catalyst does not have
to be constantly heated as the reaction is EXOTHERMICreleases heat.
Nitric Acid is used in the manufacture of fertilisers, explosives
and plastics.