Preparation: Pyrophosphoric acid (H4 P2 O7) is prepared by heating orthophosphoric acid to 523 K – 533 K.
2H3PO4 → H4P2O7 + H2O
It is a colourless crystalline solid.
- It is reconverted to orthophosphoric acid on boiling with water
H4P2O7 + H2O →2H3PO4
- When heated strongly, it yields metaphosphoric acid
H4P2O7 → 2ΗPO3 + H2O
Structure: The Structure of pyrophosphoric acid is represented as: