Uses 1. 2. 3. 4.
It is used in the preparation of HBr and HI as a substitute for sulphuric acid. It is used as souring agent in the preparation of soft drinks. It is used in the preparation of phosphate salts of sodium, potassium and ammonium. It is used in the manufacture of phosphatic fertilisers.
Structure Being a tribasic acid, the structure of phosphoric acid is represented as O
H
O x x O x P x O x O
H
H
x - E lectro n o f P - E lectro n o f O - E lectro n o f H
P
HO
OH OH
III. B. Pyrophosphoric acid, H4 P2 O7 Preparation: Pyrophosphoric acid is prepared by heating orthophosphoric acid to 523 K – 533 K. 2H3PO4 → H4P2O7 + H2O Physical Properties It is a colourless crystalline solid. Chemical Properties 1.
It is reconverted to orthophosphoric acid on boiling with water H4P2O7 + H2O → 2H3PO4
2.
When heated strongly, it yields metaphosphoric acid H4P2O7
2ΗPO3 + H2O
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