The ratio of sigma and $$\pi$$ bonds present in pyrophosphoric acid is _____.

Pyrophosphoric acid is: $$H_4P_2O_7$$

Its structure contains:

- Two phosphorus atoms
- One $$P-O-P$$ linkage
- Four $$P-OH$$ bonds
- Two $$P=O$$ bonds

Structure analysis:

Sigma bonds:

From four $$O-H$$ bonds: $$4$$

From four $$P-O$$ single bonds attached to $$OH$$: $$4$$

From one $$P-O-P$$ bridge: $$2$$

(one sigma bond from each $$P-O$$)

From two $$P=O$$ bonds: $$2 \sigma$$

Total sigma bonds: $$4+4+2+2=12$$

Pi bonds:
Each $$P=O$$ contributes one $$\pi$$ bond.

Thus: $$2 \pi \text{ bonds}$$

Therefore the ratio of sigma and $$\pi$$ bonds is: $${12:2}$$ or $${6:1}$$