Question

Find the number of P–O–P (pyrophosphate) bonds present in $P_4O_8$.

Hint:

Total oxygen atoms minus terminal P=O oxygens gives number of bridging oxygens. Each bridging oxygen corresponds to one P–O–P bond.

Answer 1

Correct Answer: 4

Step 1: Understand P–O–P bond.
A P–O–P bond is a bridging oxygen atom connecting two phosphorus atoms.
Such bonds are also called pyrophosphate linkages.
Step 2: Use oxidation state method.
In $P_4O_8$, assume oxidation state of phosphorus = $x$.
Since oxygen has oxidation state $-2$, we write:
\[ 4x + 8(-2) = 0. \]
\[ 4x - 16 = 0. \]
\[ 4x = 16. \]
\[ x = +4. \]
Step 3: Count terminal P=O bonds.
Phosphorus in +4 oxidation state generally forms:
One P=O double bond and three P–O single bonds.
Total oxygen atoms = 8.
If each phosphorus forms one terminal P=O bond, total terminal oxygens = 4.
Remaining oxygens =
\[ 8 - 4 = 4. \]
Step 4: Determine P–O–P bridges.
Each bridging oxygen connects two phosphorus atoms.
Thus number of P–O–P bonds equals number of bridging oxygens.
Hence, number of P–O–P bonds =
\[ \boxed{4}. \]