Question

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

Answer 1

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

Explanation:

`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

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

Explanation:

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.