Complete and balance:
ClO2–(aq) → ClO–(aq) + ClO4–(aq)
This is an example of a disproportionation reaction, where a single species is simultaneously oxidized and reduced.
Oxidation half–reaction (Cl goes from +3 to +7):
ClO2–(aq) + 2 H2O(l) → ClO4–(aq) + 4 H+(aq) + 4 e–
Cl is mass balanced
O balance
H balance
charge balance
Reduction half–reaction (Cl goes from +3 to +1):
ClO2–(aq) + 2 H+(aq) + 2 e– → ClO–(aq) + H2O(l)
Cl is mass balanced
O balance
H balance
charge balance
The reduction requires multiplication by a factor of 2 to equalize the number of electrons:
2 ClO2–(aq) + 4 H+(aq) + 4 e– → 2 ClO–(aq) + 2 H2O(l)
Add the two half–reactions together and eliminate species common to both sides:
3 ClO2–(aq) → 2 ClO–(aq) + ClO4–(aq)