what is the equivalent mass of KMnO4 ?

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sciftw | High School Teacher | (Level 1) Educator Emeritus

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Before being able to calculate the equivalent mass, you need to calculate the molar mass of potassium permanganate.  Looking at a periodic table and rounding works fine.  

K = 39 g/mol

Mn = 55 g/mol

O = 16 g/mol      (multiply by 4 because there are 4 oxygens)

39 + 55 + (16 x 4) = 158 g/mol

The molar mass of potassium permanganate is 158 g/mol.  To find the equivalent mass, divide that molar mass by the mols of electrons taken in its half reaction.  That would be five.  158/5 = 31.6 grams/equivalent.  

The above is the most common half reaction using potassium permanganate as an oxidizer in an acidic solution.  It can be used as an oxidizer in a basic solution too.  This is not as common, and it does yield a different answer.  This half reaction would use 3 electrons.  158/3 = 52.7 grams/equivalent.  

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