Question

Click in the answer box to activate the palette. Use the half-reaction method to balance the following equation in basic solution: Fe24 MnO4 Fe3+ + Mn2 (Do not include the states of matter.)

Answer 1

Unbalanced equation

Fe2+ + MnO4- ---> Fe3+ + Mn2+

Split it in to two halfs: oxidation and reduction

Oxidation:
Fe2+ ----> Fe3+ [oxidation number increased from +2 to +3]

reduction:
MnO4- ----> MN2+ [oxidation number reduced from +7 to +2 for Mn]

balance O atoms by adding H2O

Oxidation:
Fe2+ ----> Fe3+
reduction:
MnO4- ----> Mn2+ 4H2O

balance H atom by adding H+

Oxidation:
Fe2+ ----> Fe3+
reduction:
MnO4- + 8H+----> Mn2+ 4H2O
Since reaction in basic medium, add OH- to cancel protons added .It must be added
to both side

Oxidation:
Fe2+ ----> Fe3+
reduction:
MnO4- + 8H2O----> Mn2+ 4H2O + 8OH-

Balance the charge by adding electrons

Oxidation:
Fe2+ ----> Fe3+ +e-
reduction:
MnO4- + 8H2O- + 5e----> Mn2+ 4H2O + 8OH-

make electron lost = electron gained

Oxidation:
5Fe2+ ----> 5Fe3+ +5e-
reduction:
MnO4- + 8H2O- + 5e----> Mn2+ 4H2O + 8OH-
Add half equations to get overall

5Fe2+ MnO4- + 8H2O- + 5e-----> 5Fe3+ +5e- +Mn2+ 4H2O + 8OH-
simplify reaction by ancel out same species on opposite side of the arrow

5Fe2+ MnO4- + 4H2O- -----> 5Fe3+ +Mn2+ 8OH-
**********************
this is the required balanced equation.

Thanks !