The chemical reaction between KMnO4 and SO2 is represented by the following equation, 2KMnO4+5SO2+2H2O→K2SO4+2MnSO4+2H2SO4 Molar mass of KMnO4 is 158.034g∕mol ∴ We have number of moles of KMnO4 =
15.8g
158.034g∕mol
=0.10moles According to given equation, 2 moles of KMnO4 reacts with 5 moles of SO2. ∴0.10 moles of KMnO4 will react with
5
2
×0.10moles of SO2 i.e. 0.25 moles of SO2 . Given, SO2 is produced by roasting of iron pyrite (FeS2) as: 4FeS2+11O2→2Fe2O3+8SO2 So, 8 moles of SO2 will be formed by 4 moles of FeS2. ∴0.25 moles of SO2 will be formed by
4
8
times0.25 moles of FeS2=0.125 moles of FeS2 Molecular mass of FeS2=119.98gmol−1 ∴ Amount of FeS2 required to give necessary SO2 =119.98gmol−1×0.125mol =14.99g≈15g of FeS2