TOPIC 14

Fertilisers

Growth of PlantsGrowth 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 FixingNitrogen FixingSome 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)

Starting Materials: Nitrogen is obtained by the fractional distillation of the Air and the Hydrogen is obtained from CH4 in Natural Gas

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.

Industrial Preparation of Nitric Industrial Preparation of Nitric AcidAcid-The Ostwald Process

1. NH3(g) + O2(g) NO(g) + H20 2. NO(g) + O2(g) NO2(g)

3.. NO2 + H2O HNO3 (Nitric Acid).

Nitric Acid is used in the manufacture of fertilisers, explosives and plastics.

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 EXOTHERMIC- releases heat.

Takes place in 3 stages; with the first one being the most

difficult