Fertilisers (WJEC GCSE Chemistry)

What are fertilisers?

• Fertilisers contain substances that plants need to grow healthily and are used in agriculture
• Nitrogenous fertilisers contain a source of nitrogen as well as minerals such as potassium and phosphorus
  • Nitrogen makes chlorophyll, protein and promotes healthy leaves 
  • Potassium promotes growth and healthy fruit and flowers
  • Phosphorus promotes healthy roots
• Fertiliser compounds contain the following water soluble ions:
  • Ammonium ions, NH₄⁺ and nitrate ions, NO₃^-, are sources of soluble nitrogen
  • Phosphate ions, PO₄^3- are a source of soluble phosphorus
  • Most common potassium compounds dissolve in water to produce potassium ions, K⁺

Table of common fertiliser compounds

Name	Formula
Ammonium nitrate	NH4NO3
Ammonium phosphate	(NH4)3PO4
Potassium sulfate	K2SO4
Ammonium sulfate	(NH4)2SO4

• Ammonium salts and nitrates are commonly used as fertilisers
• Different fertilisers contain different amounts of fertiliser compounds so each contains different proportions of nitrogen, potassium and phosphorous

Producing fertilisers

• Fertilisers such as ammonium nitrate are produced by a neutralisation reaction and an ammonium salt is formed
• The salt is the fertiliser
• Ammonia is a gaseous alkali that reacts with nitric acid to form ammonium nitrate: 

NH₃ (g) + HNO₃ (aq) → NH₄NO₃ (s) 

• Ammonia also reacts with sulfuric acid to form ammonium sulfate:

2NH₃ (g) + H₂SO₄ (aq) → (NH₄)₂SO₄ (s)