(a) What happens when : (i) sulphur dioxide is passed through an aqueous solution of Fe (III) salt ?
(ii) Sulphur dioxide is passed through and aqueous solution of sodium carbonate ?
(b) On passing `H_(2)S` through an aqueous solution of `SO_(2)`, as a yellow turbidity is formed. Why ?

Explanation

(a) (i) `SO_(2)` being a reducing agent, reduces Fe (III) to Fe (II) salts.
`2overset(3+)(Fe)(aq)+SO_(2)(g) + 2H_(2)O (l) rarr 2 overset(2+)(Fe)(aq) + SO_(4)^(2-) (aq) + 4 overset(+)(H)(aq)`
(ii) Being acidic, `SO_(2)` decomposes `Na_(2)CO_(3)` forming sodium sulphite with evolution of `CO_(2)` gas.
`Na_(2)CO_(3)(aq) + SO_(2)(g) rarr Na_(2)SO_(3) (aq) + CO_(2)(g)`
(b) `H_(2)S` reduces `SO_(2)` to sulphur which appears as yellow turbidity.
`2H_(2)S + SO_(2) rarr underset(("Yellow turbidity"))(3S) + 2H_(2)O`