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

1 Answer
Jun 5, 2018

Answer:

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...