reduction :
MnO4-  ----------------------------> Mn+2
(+7)                                          ÂÂ
(+2)
total 5 electrons are transfered
MnO4-  +5e- ÂÂ
----------------------------> Mn+2
balance oxygens :
MnO4-  + 8 H+ + 5e-  ÂÂ
----------------------------> Mn+2  +
4H2O            ÂÂ
(equation 1)
oxidation :
H2SO3 -------------------------> SO4^-2
(+4)                                       ÂÂ
(+6)
two electrons are transfered
H2SO3   + 2e- ------------------------->
SO4^-2
balance oxygens
H2SO3   + H2O + 2e-
-------------------------> SO4^-2  +
4H+   (equation 2)
multiply equation (1) with 2 and multiply equation (2) with 5
and than add
2MnO4-  + 16 H+ + 5H2SO3 + 5H2O
------------------> 2Mn+2 + 8H2O + 20 H+ + 5
SO4^-2 ÂÂ
2MnO4-    + 5H2SO3 + ÂÂ
------------------> 2Mn+2 + 3H2O + 4 H+ + 5 SO4^-2
