Question

Observation of sodium sulfite solid added to a little alkaline potassium permanganate?

Answer 1

Well what did you see? The colour would dissipate certainly, but was there a brown precipitate? Did it go green..?

Explanation:

In acidic medium sulfite would be oxidized to sulfate, and permanganate reduced to `Mn^(2+)`

`SO_3^(2-) +H_2O(l)rarr SO_4^(2-) +2H^+ + 2e^-` `(i)`

And of course permanganate reduced to `Mn^(2+)`...

`MnO_4^(-) + 8H^+ +5e^(-) rarr Mn^(2+)+4H_2O` `(ii)`

But this is in an ACID medium. In a basic medium, which was specified by the question, more likely the reduction product would be manganate ion, `MnO_4^(2-)`, `Mn(VI+)`, OR `MnO_2(s)`...i.e. a hydrous oxide of `Mn(IV+)`...

For manganate ion....

`underbrace(MnO_4^(-))_"red" +e^(-) rarr underbrace(MnO_4^(2-))_"green"`

...or MORE LIKELY.....

`MnO_4^(-)+2H_2O + 3e^(-) rarr underbrace(MnO_2(s))_"brown solid"darr+4HO^-` `(iii)`

I am inclined to think that `(iii)` is the reduction that occurred. But what do I know? I did not do the experiment. And so we cross multiply...

`3xx(i)+2xx(iii)`

`3SO_3^(2-) +2MnO_4^(-) +H_2O(l)rarr2MnO_2(s)+3SO_4^(2-) + 2HO^-`

The which is balanced with respect to mass and charge... Whew.

See here for another example of this process...