A given volume of a KMnO4 solution oxidises 25.0 mL of 0.100 M FeSO4 completely in acidic medium. The same volume of this KMnO4 solution is used in neutral medium (reduction to MnO2) to oxidise a 0.0500 M Na2SO3 solution to sulphate. The volume of sulphite solution oxidised is:

JEE Advanced levelSingle correct optionDifficulty 3 of 3rx201

A given volume of a $KMnO X_{4}$ solution oxidises 25.0 mL of 0.100 M $FeSO X_{4}$ completely in acidic medium. The same volume of this $KMnO X_{4}$ solution is used in neutral medium (reduction to $MnO X_{2}$ ) to oxidise a 0.0500 M $Na X_{2} SO X_{3}$ solution to sulphate. The volume of sulphite solution oxidised is:

In acid, equivalents of permanganate = 2.50 meq (= meq of

Fe X^{2 +}

), so mmol

MnO X_{4} X^{-}

= 2.50/5 = 0.50. In neutral medium n = 3, giving

0.50 \times 3 = 1.50

meq. Sulphite has n = 2, so 0.100 N; volume = 1.50/0.100 = 15.0 mL.