What is the reaction between sulfur dioxide, #"SO"_2#, and potassium dichromate, #"K"_2 "Cr"_2"O"_7# ?

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Answer 1 · 2017-04-01T15:07:46

In presence of #"H"_2"SO"_4#,potassium dicromate reacts with #"SO"_2# as following.

#3"SO"_2# + #"K"_2"Cr"_2"O"_7# + #"H"_2"SO"_4# #-># #"K"_2"SO"_4# + #"Cr"_2("SO"_4)_3# + #"H"_2"O"#

Answer 2 · 2017-04-01T15:13:34

Well, we would assume that #"sulfur dioxide"# is oxidized to #"sulfur trioxide"#.

I think this is done industrially by #V_2O_5#.

But sulfur is oxidized to from #S(+IV)# to #S(+VI):#

#SO_2(g) +H_2O(l) rarr SO_3(g) +2H^(+) + 2e^(-)# #(i)#

And dichromate is reduced from #Cr(+VI)# to #Cr(+III):#

#Cr_2O_7^(2-) +14H^(+) +6e^(-)rarr 2Cr^(3+) +7H_2O(l)# #(ii)#

We add #3xx(i) + (ii)# to eliminate the electrons:

#Cr_2O_7^(2-) +8H^(+) +3SO_2(g) rarr 2Cr^(3+) +4H_2O(l)+3SO_3(g)#

Are mass and charge balanced? This is your problem not mine.