An amorphous solid 'A' burns in air to form a gas 'B' which turns lime water milky. The gas is also produced as a by-product during roasting of sulphide ore. This gas decolourises acidified aqueous KMnO_(4) solution and reduces Fe^(3+) to Fe^(2+). Identify the solid "A" and the gas "B" and write the reaction involved.

An amorphous solid 'A' burns in air to form a gas 'B' which turns lime

1.	An amorphous solid 'A' burns in air to form a gas 'B' which turns lime water milky. The gas is also produced as a by-product during roasting of sulphide ore. This gas decolourises acidified aqueous KMnO_(4) solution and reduces Fe^(3+) to Fe^(2+). Identify the solid "A" and the gas "B" and write the reaction involved.
Answer» Solution :(i) Since gas 'B' is obtained as a by-product during roasting of sulphide, therefore, gas 'B' must be `SO_(2)`. `2 ZnS + 3 O_(2) rarr 2 ZnO + 2 SO_(2) (B)` (ii) Since gas 'B' is obtained when AMORPHOUS SOLID 'A' burns in air, therefore, amorphous solid 'A' must be SULPHUR, `S_(8)` `S_(8) (A) + 8 O_(2) rarr 8 SO_(2) (B)` (iii) Gas 'B' reduces ACIDIFIED `KMnO_(4)` solution and reduces `Fe^(3+)` to `Fe^(2+)` salts as shown below : `{:(underset(("Purple"))(2MnO_(4)^(-)) + underset((B))(5SO_(2))+ 2H_(2)O rarr underset(("COLOURLESS"))(2Mn^(2+))+5SO_(4)^(2-) + 4H^(+)),(underset(("Yellow"))(2Fe^(3+))+underset((B))(SO_(2))+2H_(2)O rarr underset(("Green"))(2Fe6(2+)) + SO_(4)^(2-) + 4 H^(+)):}` Thus, solid 'A' = `S_(8)` and gas 'B' = `SO_(2)`.