Decompostion of H2O2

1.
The experiment involves two different redox reactions between H2O2 and MnO4-.

The first reaction is that in preparation of the reaction mixture.
2MnO4-(aq) + 3H2O2(aq) + H2­O(l) → 2MnO2(colloid) + 3H2O(l) + 2OH-(aq) + 3O2(g)

The second reaction occurs during the titration.
2MnO4-(aq) + 6H+(aq) + 5H2O2(aq) → 2Mn2+(aq) + 5O2(g) + 8H2O(l)


2.
This is to quench the decomposition of H2O2.
In the reaction mixture, all MnO4- ions added are entirely changed to MnO2 which is the catalyst of the reaction in the reaction mixture. 10 cm3 sample of the reaction mixture is pipetted into 10 cm3 of acid (an excess). In the presence of an excess of acid, MnO2 quantitatively reacts with H2O2 to give Mn2+(aq) ions.
MnO2(aq) + 2H+(aq) + 2H2O2(aq) → Mn2+(aq) + 2H2O + O2(g)
Since the catalyst is removed, the decomposition of H2O2 is practically stopped.
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