Fertilisers

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Topic 14

• Fertilisers

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Fertilisers

• Needed due to increasing demand for food
• Restore essential elements for plant growth to
  the soil (contain nutrients N, P, K)
• Natural e.g. compost, manure
• Man-made e.g. ammonium salts, potassium salts,
  nitrates, phosphates
• Physical properties-must be soluble, safe to
  handle, easy to store, easy to spread,
  non-polluting

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Nitrogen cycle
natural processes
man-made processes
these processes compounds are important
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Processes to know

• Electric storms ( car engines)
• Nitrogen is not very reactive but will form
  compounds if there is enough energy to break the
  N N
• N2 O2 2
  NO
• 2 NO O2 2 NO2
• 2 NO2 O2 H2O 4 HNO3
• Haber process
• N2 3 H2 2 NH3
• Iron catalyst, high pressure, moderate
  temperature (500oC), unreated gases recycled, NH3
  cooled and removed, 25-35 conversion
• Ostwald process
• 4 NH3 5 O2 4 NO 6 H2O
  
• (then conversion NO NO2 HNO3 as above )
• Platinum catalyst, exothermic, 500oC

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Ammonia
Nitric acid

• manufactured by the Haber Process
• made in the lab. by heating an ammonium compound
  with soda lime or warming conc. ammonia solution
• physical properties-colourless gas, lighter than
  air, strong smell, very soluble
• chemical properties
• weakly alkaline
• neutralised by acids to make ammonium salts
• e.g. NH3 HCl NH4Cl

• manufactured by the Ostwald Process
• strong acid
• neutralised by metals, alkalis, metal oxides
  (bases) and metal carbonates to make nitrate
  salts
• 2 HNO3 Mg Mg(NO3 )2 H2
• HNO3 NaOH Na NO3 H2O
• 2 HNO3 ZnO Zn(NO3 )2 H2O
• 2 HNO3 CuCO3 Cu(NO3 )2 H2O CO2
• reacts with copper when concentrated
• Cu 4HNO3 Cu(NO3 )2 2H2O 2NO2