When potassium permanganate is titrated against ferrous ammonium sulphate, the equivalent weight of potassium permanganate is: (M= Molecular weight)

1. M/10
2. M/5
3. M/2
4. M

Do explain your answer.

Dear student

Molecular Weight of Mohr's Salt is 'M'
KMnO4 will oxidise Fe2+ ion to Fe3+ and will itself reduce to Mn2+
Fe2+ changes it's oxidation state by 1. Hence N-Factor or Valence Factor of Fe in Mohr's Salt is 1 and hence Equivalent Weight=Molecular Weight/N-Factor = M/1 = 1
n-factor of KMnO4, is 5 hence it's equivalent weight is one fifth of it's molecular weight.