Balancing Redox Reactions

Question

Complete and balance the following redox reaction in acidic solution. Be sure to include the proper phases for all species within the reaction.

MnO4 -(aq)+S2O3 2-(aq) --> S4)6 2-(aq)+Mn 2+(aq)

Answer 1

MnO₄^-(aq) ==> Mn²⁺(aq) .. unbalanced reduction reaction

MnO₄^-(aq) ==> Mn²⁺(aq) + 4H₂O(l) .. balanced for Mn and O

MnO₄^-(aq) + 8H⁺(aq) ==> Mn²⁺(aq) + 4H₂O(l) .. balanced for Mn, O and H using acid (H⁺)

MnO₄^-(aq) + 8H⁺(aq) + 5e- ==> Mn²⁺(aq) + 4H₂O(l) .. balanced for mass and charge = balanced equation

S₂O₃^2-(aq) ==> S₄O₆^2-(aq) .. unbalanced oxidation reaction

2S₂O₃^2-(aq) ==> S₄O₆^2-(aq) .. balanced for S and O

2S₂O₃^2-(aq) ==> S₄O₆^2-(aq) + 2e- .. balanced for mass and charge = balanced equation

Multiply reduction reaction by 2 and oxidation by 5 in order to equalize electrons. Then add the two reactions and combine/cancel like terms to obtain the final balanced redox equation.

2MnO₄^-(aq) + 16H⁺(aq) + 10e- ==> 2Mn²⁺(aq) + 8H₂O(l)

10 S₂O₃^2-(aq) ==> 5 S₄O₆^2-(aq) + 10e-

--------------------------------------------------------------------------------------

2MnO₄^-(aq) + 16H⁺(aq) + 10 S₂O₃^2-(aq) ==> 2Mn²⁺(aq) + 8H₂O(l) + 5 S₄O₆^2-(aq) .. balanced redox eq.