Balance the following redox reaction in acidic medium:
MnO−4+SO2⟶SO2−4+Mn2+
A
2MnO−4+5SO2+2H2O⟶5SO2−4+2Mn2++4H+
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B
2MnO−4+3SO2+2H2O⟶5SO2−4+2Mn2++6H+
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C
2MnO−4+3SO2+2H2O⟶3SO2−4+2Mn2++4H+
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D
None of these
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Solution
The correct option is C2MnO−4+5SO2+2H2O⟶5SO2−4+2Mn2++4H+ The unbalanced redox equation is as follows:
MnO−4+SO2⟶SO2−4+Mn2+(acidic)
All atoms other than H and O are balanced. The oxidation number of Mn changes from +7 to +2. The change in the oxidation number per Mn atom is 5. The oxidation number of S changes from +4 to +6. The change in the oxidation number is 2.
To balance the increase in the oxidation number with decrease in the oxidation number multiply MnO−4 and Mn2+ with 2 and multiply SO2 and SO2−4 with 5.
2MnO−4+5SO2⟶5SO2−4+2Mn2+
To balance O atoms add 2 water molecules on LHS and to balance H atoms, add 4 H+ on RHS.