[Carmel]

Hi 
Ive got problems with understanding redox reacions. Let's take a look at this reaction:
2KMnO4 + K2SO3 + 2KOH → 2K2MnO4 + K2SO4 + H2O
See, SO3  2- turns into SO4 2- so the oxidation number changes from 4 to 6 but amount of the valence electrons just doesn't change. But in half - reaction we write that it "loses" 2 electrons. Why and how this losing happens if valence electrons stay the same in SO3 2- and SO4 2-? Does anyone understand that?Please, help

[Borek]

If you try to write half oxidation half reaction for SO₃^2- SO₄^2-, you won't be able to balance it without electrons. Charge conservation takes care of that. So, whatever you mean by "amount of the valence electrons just doesn't change" it doesn't matter, whether it is right or wrong.

[Hunter2]

Additionally in Sulfite only 4 elektrones are bonded to Oxygen. Sulfur has still one pair of not bonded electrons which will be taken if it converts to Sulfate.