1.

How is the presence of SO_(2) detected ?

Answer»

Solution :`SO_(2)` is a PUNGENT smelling gas. It can be detected by the following two tests :
(i) `SO_(2)` turns the pink violet colour of `KMnO_(4)` solution colourless DUE to reduction of `MnO_(4)^(-)` to `MN^(2+)` ions.
`underset(("pink violet"))(2 MnO_(4)^(-))+5SO_(2) + 2H_(2)O rarr underset(("colourless"))(2 Mn^(2+)) + 5 SO_(4)^(2-)+4H^(+)`
(ii) `SO_(2)` turns orange coloured acidified `K_(2)Cr_(2)O_(7)` solution green due to reduction of `CrO_(7)^(2-)` to `Cr^(3+)` ions.
`underset(("orange"))(Cr_(2)O_(7)^(2-))+3SO_(2) + 2 H^(+) rarr 2 Cr^(3+) + 3 SO_(4)^(2-) + H_(2)O`


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