Question

Balance the following half-reaction under basic conditions. PO3− → PH3

Answer 1

Step 1: Write the half reaction.

PO₃^- PH₃

Step 2: Add required number of H2O to balance O atoms.

PO₃^- PH₃ + 3 H₂O

Step 3: Add required number of H⁺ to balance H atoms.

9 H⁺ + PO₃^-   PH₃ + 3 H₂O

Step 4: Since medium is basic add equal number of OH^- as H⁺ to both sides

9 H⁺ + 9 OH^- + PO₃^-   PH₃ + 3 H₂O + 9 OH^-

Step 5: Add OH^- as H⁺ to form H₂O

9 H₂O+ PO₃^-   PH₃ + 3 H₂O + 9 OH^-

= 6 H₂O+ PO₃^-   PH₃ + 9 OH^-

Step 6: Finally balance the charges by adding or subtracting required number of electrons.

6 H₂O+ 8 e^- + PO₃^-   PH₃ + 9 OH^-