Question

How is the presence of SO₂ detected?

Answer 1

SO₂ is a colourless and pungent smelling gas.

It can be detected with the help of potassium permanganate solution. When SO₂ is passed through an acidified potassium permanganate solution, it decolonizes the solution as it reduces `MnO_4^(-)` ions to `Mn^(2+)`  ions

`5SO_2 + 2MnO_4^(-) + 2H_2O -> 5SO_4^(2-) + 4H^(+) + 2Mn^(2+)`

Answer 2

SO₂ is a pungent smelling gas. It can be detected by two test:

SO₂ turn pink color of KMnO4 to colourless due to reduction of `MnO_4^(-)` to `Mn^(2+)`

`2MnO_4^(-) + 5SO_2+ 2H_2O -> 2Mn^(2+)  + 5SO_4^(2-) + 4H^(+)`

(Pink)                                                (colourless)

 

2) It turn orange colour of acidified `K_2Cr_2O_7` to green due to reduction of `Cr_2O_7^(2-)` to `Cr^(3+)`

`Cr_2O_7^(2-) + 3SO_2 + 2H^(+) -> 2Cr^(3+) + 3SO_4^(2-) + H_2O`

(orange)                                        (green)