5.4 CHAPTER 5. THE CHEMICAL INDUSTRY
Ca(NO 3 ) 2 + 4H 3 PO 4 + 8NH 3 → CaHPO 4 + 2NH 4 NO 3 + 8(NH 4 ) 2 HPO 4
If potassium chloride orpotassium sulphate is added, the result will be NPK
fertiliser.
(d) Other nitrogen fertilisers
- Urea ((NH 2 ) 2 CO) is a nitrogen-containing chemical productwhich is
produced on a large scale worldwide. Urea has the highest nitrogen
content of all solid nitrogeneous fertilisers in common use (46.4%) and
is produced by reactingammonia with carbon dioxide.
Two reactions are involved in producing urea:
i. 2NH 3 + CO 2 → H 2 N− COONH 4
ii. H 2 N− COONH 4 → (NH 2 ) 2 CO + H 2 O
- Other common fertilisers are ammonium nitrate and ammonium sul-
phate. Ammonium nitrate is formed by reacting ammonia with nitric
acid.
NH 3 + HNO 3 → NH 4 NO 3
Ammonium sulphate isformed by reacting ammonia with sulphuric
acid.
2NH 3 + H 2 SO 4 → (NH 4 ) 2 SO 4
- Phosphate fertilisers
The production of phosphate fertilisers also involves a number of processes. The
first is the production of sulphuric acid throughthe contact process. Sulphuric
acid is then used in a reaction that produces phosphoric acid. Phosphoric acid
can then be reacted withphosphate rock to produce triple superphosphates.
(a) The production of sulfuric acid
Sulfuric acid is produced from sulphur, oxygenand water through the con-
tact process. In the firststep, sulphur is burned to produce sulphur dioxide.
S(s) + O 2 (g)→ SO 2 (g)
This is then oxidised tosulphur trioxide using oxygen in the presence of a
vanadium(V) oxide catalyst.
2SO 2 + O 2 (g)→ 2SO 3 (g)
Finally the sulphur trioxide is treated with waterto produce 98-99% sulfuric
acid.
SO 3 (g) + H 2 O(l)→ H 2 SO 4 (l)
(b) The production of phosphoric acid
The next step in the production of phosphatefertiliser is the reactionof
sulfuric acid with phosphate rock to produce phosphoric acid (H 3 PO 4 ). In
this example, the phosphate rock is fluoropatite(Ca 5 F(PO 4 ) 3 ).
Ca 5 F(PO 4 ) 3 + 5H 2 SO 4 + 8H 2 O→ 5CaSO 4 + HF + 3H 3 PO 4
(c) The production of phosphates and superphosphates
When concentrated phosphoric acid reacts with ground phosphate rock,
triple superphosphate isproduced.
