Question

The equivalent weight of Potassium permanganate in acidic medium is:

• A. 31.6
• B. 51.6
• C. 41.6
• D. 21.6

Answer 1

The Correct Option is A

The correct option is (A): 31.6.

Answer 2

The equivalent weight of an oxidizing agent depends on the number of electrons it gains per molecule, which changes with the medium it reacts in. In acidic medium, manganese in KMnO4 goes from the +7 state down to the +2 state (as Mn2+), a change of 5 electrons. Let's check each option against this.

1. 31.6: The molecular weight of KMnO4 is 158. Dividing by the 5-electron change gives \( \frac{158}{5} = 31.6 \), which matches exactly what happens when Mn7+ is reduced all the way to Mn2+ in an acidic solution.
2. 51.6: This number does not come from dividing 158 by a whole electron count that manganese can undergo. If Mn7+ were reduced only to Mn4+ (as MnO2, in a neutral or weakly alkaline medium), the change would be 3 electrons, giving \( \frac{158}{3} \approx 52.7 \), close to but not exactly this value, and in any case that reaction happens in neutral medium, not acidic medium.
3. 41.6: There is no valid oxidation state change of manganese in the KMnO4 system that divides 158 into this number, so it does not correspond to any real reduction step.
4. 21.6: Likewise, this value cannot be reached by dividing 158 by 1, 3, or 5, the only electron changes manganese actually undergoes in the three common media (alkaline, neutral, acidic), so it can be ruled out too.

Only the acidic-medium pathway, with its 5-electron change, gives a clean, exact equivalent weight from the molecular weight of KMnO4.

So the correct answer is 31.6.