Question

Molecular weight of mohr's salt is 392.it's equivalent weight when it is oxidised by kmno4 in acidic medium is?

Answer 1

Formula
(NH₄)₂Fe (SO₄).6H₂O
the only oxidisable atom here is Fe in its +2 oxidation state .
Therefore whole of the molecule when oxidised will need to to release only one electron (by Fe 2+)
Therfore it's equivalent weight is 392/1
392

Answer 2

the equivalent weight of Mohr salt is asked, when it is reacted with KMnO4.

lets see the reaction first,

2KMnO4 +10FeSO4 .(NH4)2SO4.6H2O+8H2SO4 →K2SO4 +2MnSO4 +10(NH4)2SO4+5Fe2(SO4)3 +8H2O Mn oxidation state = +7 to +2so equivalent weight of KMnO4=mol wt of KMnO45Fe of mohr salt =+2 to +3so equivalent weight of mohr salt=mol wt of mohr salt1=3921 = 392 g/mol

hope the concept is clear to you

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