Step 1: Separate the whole reaction into two half-reactions
HCOOH → CO2 MnO4- → Mn2+
Step 2: Balance the non-hydrogen and non-oxygen elements first
HCOOH → CO2 MnO4- → Mn2+
(C is balanced) (Mn is balanced)
Step 3: Balance oxygen by adding H2O(l) to the side that needs oxygen (1 O : 1 H2O)
HCOOH → CO2 MnO4- → Mn2+ + 4H2O
Step 4: Balance hydrogen by adding H+ to the side that needs hydrogen (1 H: 1 H+)
HCOOH → CO2 + 2H+ 8H+ + MnO4- → Mn2+ + 4H2O
Step 5: Balance the charges: add electrons to the more positive side (or less negative side)
HCOOH → CO2 + 2H+ 8H+ + MnO4- → Mn2+ + 4H2O
Reactants Products Reactants Products
HCOOH = 0 2H+ = +2 8H+ =+8 Mn2+ =+2
__MnO4- = -1________________________
Overall = 0 +2 +7 overall = +2
+2e- +5e-
0 +2
Step 6: Balance electrons on the two half-reactions
5[HCOOH → CO2 + 2H+ +2e-]
2[5e- + 8H+ + MnO4- → Mn2+ + 4H2O]
5HCOOH → 5CO2 + 10H+ + 10e-
10e- + 16H+ + 2MnO4- → 2Mn2+ + 8H2O
Step 7: Get the overall reaction by adding the two reaction.
5HCOOH → 5CO2 + 10H+ + 10e-
10e- + 16H+ + 2MnO4- → 2Mn2+ + 8H2O
5HCOOH + 6H+ + 2MnO4- → 2Mn2+ + 8H2O + 5CO2
Balanced Redox Reaction:
5HCOOH + 6H+ + 2MnO4- → 2Mn2+ + 8H2O + 5CO2
