CIE AS Chemistry (9701) 2019-2021

Revision Notes

2.4.2 Uses of Nitrogen Compounds

Uses of Ammonia & Nitrogen Compounds

  • Ammonia and nitrogen compounds have a wide range of industrial purposes

Ammonia

  • Ammonia is used in the manufacturing of fertilisers which are used to grow crops
    • Plants are unable to directly use the nitrogen that is present in the air
    • Instead, they get their nitrogen from nitrogen compounds dissolved in water which they can absorb from the soil through their roots
    • Without the use of fertilisers, crops will not be able to grow resulting in lack of food to feed the population
    • Some ammonia is injected directly into the soil to act as a fertiliser
  • Ammonium hydroxide, also known as household ammonia is used as the main ingredient in many household cleaning products
  • Ammonia is also used as a refrigerant gas as it absorbs heat from the surroundings

Nitric acid

  • Another purpose of ammonia is in the synthesis of nitric acid
  • Nitric acid is used to form dyes but is also used in fertilizers
  • Other uses of this nitrogen compound include making explosives (such as TNT)

Environmental Consequences of Fertilisers

  • The uncontrolled use of nitrate fertilisers can have significant environmental problems
    • Ammonium salts are soluble in water and get washed in to the ground water, rivers and streams causing them to get contaminated with ammonium and nitrate ions
    • This results in eutrophication of streams and rivers
    • When ammonium salts in fertilisers get into the water, there is an increase in plant nutrients
    • Algae that live in the water will feed on these nutrients causing excessive growth of the algae
    • As a result, light cannot reach the lower plants in the water, preventing them from photosynthesising, causing them to die
    • Bacteria feed on the dead plants which decompose by aerobic respiration
    • All the oxygen is used up by the decaying plants, which means that organisms can no longer respire
  • Nitrates are also potentially carcinogenic
    • The presence of nitrates in drinking water is dangerous to human health
    • The removal of nitrates from water is too expensive
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