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 sulphideore. This gas decolourises acidified aqueous KMnO4 solution and reduces Fe3+ to Fe2+. Identify the solid “A” and the gas “B” and write the reactions involved.

the amorphous solid A is sulphur (s8) while gas b is sulphur dioxide.

S8 + 8O28SO2


The gas SO2 turns the lime water milky.


Roasting of sulphide ore :


2ZnS + 3o22ZnO + 2SO2


Hence sulphur dioxide is produced during the roasting of sulphide ore.


The gas B decolourise the acidified KMnO4 solution and reduces Fe3+ to Fe2+


2KMnO4 + 5SO2 +2H2O K2SO4 + 2MnSO4 + 2H2SO4


Fe(SO4)3 + SO2 + 2H2O 2FeSO4 + 2H2SO4


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