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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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