Fertilisers (Cambridge International IGCSE Chemistry)

Spec point — 10.1.4 · State that ammonium salts and nitrates are used as fertilisers Describe the use of NPK fertilisers to provide the elements nitrogen, phosphorus and potassium for improved plant growth

Fertilisers

NPK fertilisers

• NPK fertilisers contain nitrogen, potassium and phosphorus for improved plant growth

  • Nitrogen makes chlorophyll and 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⁺

• Ammonium salts and nitrate salts are commonly used as fertilisers, including:

  • Ammonium nitrate, NH₄NO₃
  • Ammonium phosphate, (NH₄)₃PO₄
  • Potassium nitrate, KNO₃

• Different fertilisers contain different amounts of fertiliser compounds

  • So, each fertiliser contains different proportions of nitrogen, potassium and phosphorous

Exam Hint You may be asked to select a compound or combination of compounds from a list which would be the most effective as a fertiliser.

Look for the compound or combination of compounds that contain the most elements from nitrogen, phosphorous and potassium.