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Topic 14 Fertilisers

Explore natural and synthetic fertilisers, their elements, the role of leguminous plants, and how to calculate element mass in compounds. Learn what makes a good fertiliser and how synthetic fertilisers are made.

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Topic 14 Fertilisers

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  1. Topic 14 Fertilisers kathryn thumath KThumath Saint Paul's 12/3/02

  2. What are Fertilisers? • Fertilisers are substances we add to the soil to replace essential elements that plants need to grow. • They can be natural or synthetic. • We need fertilisers because we are exhausting the soils natural nutrients due to increasing demands for foods. • This is because the worlds population is increasing. KThumath Saint Paul's 12/3/02

  3. Natural Fertilisers • Natural fertilisers can be split into two groups: Compost and Manure • Compost – is made from rotting plants. • Manure – is animal waste • When both plants and animals die they rot releasing ammonium compounds into the ground. • Bacteria in the soil convert these to nitrates which can then dissolve and be taken in by plants. This is part of the “Nitrogen Cycle” KThumath Saint Paul's 12/3/02

  4. Synthetic Fertilisers • These are man made and contain the three essential plant elements: • Nitrogen • Potassium • Phosphorous Known collectively as NPK Each synthetic fertiliser will contain a different amount of each element. KThumath Saint Paul's 12/3/02

  5. Leguminous Plants • These are plants which contain bacteria in special root nodules. • The bacteria are able to use Nitrogen from the Air to make Nitrates. • This is called Nitrogen Fixation • Examples of legumes – clover, beans or peas. KThumath Saint Paul's 12/3/02

  6. What makes a good Fertiliser? • They must contain essential elements (NPK) • They must be soluble – to enable absorption by plant roots. • However if they are too soluble they may be washed away with rain! • They must be easy to spread. • Urea is exception – only slightly soluble but has very high Nitrogen content. KThumath Saint Paul's 12/3/02

  7. Making Synthetic Fertilisers • They are salts made in neutralisation reactions. • Example Ammonia + Nitric Acid= Ammonium nitrate KThumath Saint Paul's 12/3/02

  8. Calculating % mass of an element in a compound. • Step 1 – Calculate correct formula of compound. Calculate 1 mole. • Step 2 - Count the number of atoms of the particular element in the compound. Add up the total mass of that element in the compound. • Step 3 -Use the equation – • % mass of element= Mass of element in compound/ total mass of compound. X 100 KThumath Saint Paul's 12/3/02

  9. Worked Example • Calculate the % mass of Nitrogen in Ammonium nitrate • Step 1 – Formula = NH4NO3 - 1 Mole = ( 2xN) + (3xO) + (4xH) =80g • Step 2 – No. of N in compound =2( 2x14 = 28) • Step3 - Mass of N in compound/Total Mass of compound x 100 • Answer – 28/80 x 100 = 35% KThumath Saint Paul's 12/3/02

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