FertilisersFertilisersIGCSE ChemistryIGCSE Chemistry

AmmoniaAmmonia

Ammonia is a colourless gas.It is highly soluble in water.It has choking smell.Ammonia is an alkaline gas.It turns the litmus colour from

red to blue.Ammonia is a weak alkali.

Ammonium compoundsAmmonium compoundsFormula for ammonia is NH3Compounds of ammonia are called

ammonium NH4+Examples of ammonium compounds:Ammonium chloride, ammonium

sulphate, ammonium nitrate, ammonium phosphate etc.

Ammonium ion is tested by heating it with sodium hydroxide and test using a litmus paper. The litmus colour changes to blue.

This is due to the formation of ammonia gas when ammonium compound is heated with alkali

FertilisersFertilisersFertilisers are used to improve the quality

of soil for proper plant growth.The three important elements plants

require for proper growth are:Nitrogen, Phosphorus and Potassium (NPK)Plants are not able to absorb or use

nitrogen in the air (about 78-80%) (nitrogen in the air is inert and so not useful for plants directly).

Nitrogen should be converted to nitrogen containing compounds before it is absorbed by plants.

Nitrogen is important for plants because it is a must when they make proteins.

Nitrates NONitrates NO3-3-Nitrates are nitrogen containing

compoundsSo many nitrates are used as fertilisers.Test for nitrates: Heat a little of the nitrate with a some

aluminium powder (or foil) and sodium hydroxide solution. Show a litmus paper at the mouth of the test tube. It should turn blue (because ammonia gas is produced in the test)

Nitrogen fixationNitrogen fixationNitrogen fixing bacteria living in the root

nodules of certain plants (pea, bean etc) convert atmospheric nitrogen to ammonia and nitrates.

Nitrogen fixationNitrogen fixation

The conversion of nitrogen to useful nitrogen compounds is called nitrogen fixation.

During thunder-storms, nitrogen and oxygen in the air react to for nitrogen oxides.

Nitrogen oxides dissolve in rain water to form dilute nitric and nitrous acids.

These acids help to make nitrogen salts when reacting with compounds in the soil.

Compounds important for Compounds important for fertiliser manufacturefertiliser manufacture

Ammonia, Sulphuric acid and Nitric acid are important compounds to manufacture fertilisers.

Ammonia is manufactured by Haber processN2 + 3H2 2NH3 (reversible reaction)

This reaction needs Iron as catalyst. Sulphuric acid is manufactured by Contact

process.First sulphur is changed to sulphur dioxide.S + O2 SO2

Then sulphur dioxide is oxidised to sulphur trioxide

SO2 + O2 SO3 (reversible reaction)

This reaction needs Vanadium (V)oxide as catalyst.

Sulphur trioxide is then dissolved in water to get sulphuric acid

SO3 + H2O H2SO4

Nitric acidNitric acid

First, ammonia is oxidised to nitrogen dioxide.Ammonia + Oxygen Nitrogen dioxide4NH3 + 7O2 4NO2 + 6H2OThis reaction needs platinum catalyst at 850 CNitrogen dioxide is mixed with water with

more oxygen produces nitric acid.Nitrogen dioxide + water + Oxygen Nitric

acid4NO2 + O2 + 2H2O 4HNO3

LeachingLeaching

leaching is the removal of a important minerals from soil by rain water.

Nitrate is important for the plant growth and so leaching of nitrate is a big problem for soil.

Leaching of potassium or phosphates is not problematic because these can be easily come back to soil by natural means

Important fertilisersImportant fertilisers

Ammonium sulphate (NH4)2SO4

Ammonium nitrate NH4NO3

Potassium sulphate K2SO4

Ammonium phosphate (NH4)3PO4

Find out which fertilizer contains highest amount of nitrogen

THE END