UPSEE 2018 Solved Paper

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