Question

Question 8.21 The Mn3+ ion is unstable in solution and undergoes disproportionation to give Mn2+, MnO2, and H+ ion. Write a balanced ionic equation for the reaction.

Class XI Redox Reactions Page 274

Answer 1

Oxidation Reaction
Mn+3 --> MnO2
Balance by adding electrons
Mn+3 --> MnO2 + e-
Mn+3 + H2O --> MnO2  + 4H+  + e-
Reduction Reaction
Mn+3 --> Mn+2
Balance by adding electrons
Mn+3  + e- --> Mn+2

Adding equations 1 and 2

2Mn+3 + 2H2O --> MnO2 + Mn+2 + 4H+


i hope it will help you
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Answer 2

the skeletal equation of this reaction is ,
               o.n increases
             |-------------------------|
          Mn³⁺ -----> Mn²⁺  + MnO₂ + H⁺
             |-------------|
          o.n decreases
reduction half reaction,
     Mn³⁺  ----------> Mn²⁺ - e⁻
oxidation half reaction,
    Mn³⁺ + 2H₂O-------------> MnO₂  + 4H⁺ + e⁻

add both reactions we get,
    2Mn³⁺ + 2H₂O -------------> Mn²⁺ + 4H⁺ + MnO₂ balanced redox reaction