Balance the following equations in basic medium by ion-electron method and oxidation number methods and identify the oxidising agent and the reducing agent.
Cl2O7(g) + H2O2(aq) → ClO–2(aq) + O2(g) + H+
The oxidation number of Cl decreases from + 7 in Cl2O7 to + 3 in and the oxidation number of ClO2- increases from – 1 in H2O2 to zero in O2. Hence, in this reaction, Cl2O7 is the oxidizing agent and H2O2 is the reducing agent as could be clearly seen in the figure below: -
Solving by ion–electron method:
The oxidation half equation is:-
The oxidation number is balanced by adding 2 electrons as:-
The charge is balanced by adding 2OH- ions as:-
The oxygen atoms are balanced by adding 2H2O as:-
The reduction half equation is:-
The Cl atoms are balanced as:-
The oxidation number is balanced by adding 8 electrons as:-
The charge is balanced by adding 6OH- as:-
The oxygen atoms are balanced by adding 3H2O as:-
Multiplying the oxidation half reaction by 4 and then adding it to the reduction half reaction, we get the net balanced reaction equation as:-
Solving by oxidation number method:
Total decrease in oxidation number of Cl2O7= 4 × 2 = 8 Total increase in oxidation number of H2O2 = 2 × 1 = 2 .Now multiplying H2O2 and O2 with 4 to balance the increase and decrease in the oxidation number, we get:
The Cl atoms are balanced as:-
The O atoms are balanced by adding 3H2O as:-
The H atoms are balanced by adding 2OH- and 2H2O to get the desired balance equation :-
