How to find equivalent weight..??

Question

i know how to find equivalant weight of acids & base... but i want to know how to find equivalant weight of oxidizing & reducding agents... like KMNO4 & Sodium Hydrosulphite

Answer 1

KMnO4 has a Molar mass of 158.04 g/mol

to find its equivalent weight as an oxidizer we need to divide the Molar mass by the moles of electrons taken in its half reaction

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the less common half reaction, uses KMnO4 as an oxidizer in an basic solution:

KMnO4 (takes 3 electrons) & OH- --> MnO2 (s)

in which case your answer comes form:

158.04 g/mol divided by 3 moles of e- =

Your less commonly used answer = 52.68 grams / equivalent

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the most common half reaction, uses KMnO4 as an oxidizer in an acidic solution:

KMnO4 (takes 5 electrons) & 8 H+ --> Mn+2

in which case your answer comes form:

158.04 g/mol divided by 5 moles of e- =

Your most widely used answer = 31.61 grams / equivalent

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Sodium Hydrosulphite, formula Na2S2O4, Molar mass 174.1 g /mol ... is used as a reducing agent in aqueous solutions

is more difficult to answer: for several reactions can take place, see:

http://books.google.com/books?id=0TamObs...

this reference has three reactions, the first is not a net redox,

I have corrected their misprints in the next two reactions:

1 Na2S2O4 & 2NaOH & O2 (4 electrons lost) --> Na2SO3  &  Na2SO4 & H2O

therefor your equivalent weight = Molar mass 174.1g / 4 moles of e- taken=

your answer is = 43.52 grams / equivalent

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1 Na2S2O4 & 2NaOH & 3H2O2  (6 electrons lost)-->  2 Na2SO4 & 4 H2O

efor your equivalent weight = Molar mass 174.1g / 6 moles of e- taken=

your answer is = 29.02 grams / equivalent