(a)The O.N. (oxidation number) of P decreases from 0 in P4 to – 3 in PH3 and increases
from 0 in P4 to + 2 in HPO2- . Hence, P4 acts both as an oxidizing agent and a reducing agent in this reaction. Ion–electron method:
The oxidation half equation is:
The P atom is balanced as:
The O.N. is balanced by adding 8 electrons as:
The charge is balanced by adding 12OH– as:
The H and O atoms are balanced by adding 4H2O as:
The reduction half equation is:
The P atom is balanced as
The O.N. is balanced by adding 12 electrons as:
The charge is balanced by adding 12OH– as:
The O and H atoms are balanced by adding 12H2O as:
By multiplying equation (i) with 3 and (ii) with 2 and then adding them, the balanced chemical equation can be obtained as:
