Explain the following with the help of balanced chemical equation :
(a) Bleaching action of `SO_(2)`.
Dehydration of formic acid by concentrated `H_(2)SO_(4)`.
Burning of benzene in presence of excess of dioxygen .

Explanation

(a) `SO_(2)` is used as bleaching agent in the presence of moisture. It bleaches due to reduction and bleaching action is temporary.
`SO_(2)+2H_(2)OrarrH_(2)SO_(4)+2[H]`
(b) `underset(("Formic acid"))(HCO OH) underset(("Dehydration"))overset(H_(2)SO_(4))rarr CO+H_(2)O`
Conc. `H_(2)SO_(4)` is a powerful dehydrating agent.
(c) Benzene burns in excess of dioxygen to form carbon dioxide and water.
`C_(6)H_(6)+(15)/(2) O_(2) rarr 6CO_(2)+3H_(2)O`