If M is the molecular weight of KMnO4, what is the equivalent mass of KMnO4 when it is converted into K2MnO4?

The equivalent mass of a substance is the ratio of molecular mass to the number of electrons gained (or lost) or change in the oxidation state. That is,

equivalent mass = molecular mass/number of electrons gained or lost or

= molecular mass/change in oxidation state

Here, potassium permanganate changes to potassium manganate. The relevant chemical reaction is:

 

Only 1 electron is gained by permanganate ion to convert to manganate ion. We can also see that the oxidation state of manganese is +7 in permanaganate ion and it changes to +6 in manganate ion. That is, the oxidation state changes by 1.

Thus, the equivalent mass = molecular mass/1 = molecular mass = M

Hence, the equivalent mass of KMnO4 is M when it converts over to K2MnO4. 

Hope this helps.