Here's the equation:
K4Fe(CN)6 + H2SO4 + KMnO4 ---> MnSO4 + Fe2(SO4)3 + K2SO4 + KNO3 + CO2 + H2O
Solution:
Steps 1 through 4 are the same as in the solution to problem #2. I'll pick up with a new step 5:
5) Add 'em up (eliminate duplicate water and hydrogen ion):
10Fe2+ + 376H+ + 122MnO4¯ + 60CN¯ ---> 10Fe3+ + 122Mn2+ + 188H2O + 60NO3¯ + 60CO2
6) Add 40 potassium ions:
10K4Fe(CN)6 + 376H+ + 122MnO4¯ ---> 10Fe3+ + 122Mn2+ + 188H2O + 40K+ + 60NO3¯ + 60CO2
7) Add 15 sulfates:
10K4Fe(CN)6 + 15H2SO4 + 346H+ + 122MnO4¯ ---> 5Fe2(SO4)3 + 122Mn2+ + 188H2O + 40KNO3 + 20NO3¯ + 60CO2
8) Add 122 sulfates:
10K4Fe(CN)6 + 137H2SO4 + 102H+ + 122MnO4¯ ---> 5Fe2(SO4)3 + 122MnSO4 + 188H2O + 40KNO3 + 20NO3¯ + 60CO2
9) Add 122 potassium ions:
10K4Fe(CN)6 + 137H2SO4 + 102H+ + 122MnO4 ---> 5Fe2(SO4)3 + 122MnSO4 + 188H2O + 60KNO3 + 102K+ + 60CO2
10) Add 51 sulfate ions:
10K4Fe(CN)6 + 188H2SO4 + 122MnO4 ---> 5Fe2(SO4)3 + 122MnSO4 + 188H2O + 60KNO3 + 51K2SO4 + 60CO2