Question

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 \[\ce{KMnO4}\] solution and reduces \[\ce{Fe^{3+}}\] to \[\ce{Fe^{2+}}\]. Identify the solid “A” and the gas “B” and write the reactions involved.

Answer 1

‘A’ is \[\ce{S8}\] ‘B’ is \[\ce{SO2}\] gas

\[\ce{S8 + 8O2  ->[Δ] 8SO2}\]

\[\ce{\underset{(violet)}{2MnO^{-}_{4}} + 5SO2 + 2H2O -> 5SO^{2-}4 + 4H^{+} + \underset{(colourless)}{2Mn^{2+}}}\]

\[\ce{2Fe^{3+} + SO2 + 2H2O -> 2Fe^{2+} + SO^{2-}4 + 4H^{+}}\]