4.0 Nitrogen and its Compounds

4.4.7 Nitrogenous fertilizers

Examine the pictures of various nitrogenous fertilizers presented below.

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Questions 4.4.7(a)

1. What is the role of fertilizers?
2. Why has the use of fertilizers become much more important today than in the past?
3. Explain why are some fertilizers are classified as nitrogenous.
4. What are the essential elements for the growth of plants, including crops?
5. Why is ammonia suitable as a raw material for the manufacture of nitrogenous fertilizers?
6. The chemical formula of urea, a nitogenous fertilizer, is (NH₂)₂CO. Which of the nitrogenous fertilizers in the pictures above is not a salt? Explain your choice.

Answers to Questions 4.4.7(a)

Nitrogenous fertilizers include ammonium sulphate, ammonium nitrate, ammonium phosphate, calcium ammonium nitrate, and urea (NH₂)₂CO.

Questions 4.4.7(b)

1. Write the chemical formulae of
   1. ammonium sulphate
   2. ammonium nitrate
   3. ammonium phosphate
2. Name the acid that you would react with ammonia to produce the following fertilizers.
   1. ammonium sulphate
   2. ammonium nitrate
   3. ammonium phosphate
3. Complete the following chemical equations to represent the manufacture of some nitrogenous fertilizers. NB: The first three are direct combination reactions, with one product only.
   1. NH₃(g) + H₂SO₄(l)
   2. NH₃(aq) + HNO₃(aq)
   3. NH₃(g) + H₃PO₄(aq)
   4. NH₃(aq) + CO₂(g)
4. Calculate the percentage by mass of nitrogen in
   1. ammonium sulphate
   2. ammonium nitrate
   3. urea
   4. hence determine the fertilizer that would be priced the highest among the three. (N = 14; H = 1; S = 32; O = 16; C = 12)
5. Nitrogen and phosphorus are both useful to plants.
   1. Determine the percentage by mass of useful elements in ammonium phosphate
   2. Which of the fertilizers ammonium phosphate and ammonium nitrate is expected to be priced higher?

Answers to Questions 4.4.7(b)