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 :-



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