Question

What is the charge of `Mn` in `KMnO_4`?

Answer 1

Well, the oxidation state of the metal centre is `+VII`.

Explanation:

But the charge on the permanganate ion is `-1`. You have its potassium salt, i.e permanganate is the counterion to `K^+`, and thus it is reasonable that we have a `MnO_4^-` ion. In other words, the charge on the OVERALL ION is `-1`; it might lie on the metal or more likely the oxygen, but it is there.

When permanganate is reduced, it goes down to `Mn(+II)`, a `d^5` system that is almost colourless. This makes the redox couple very useful for titrations because chemical change can be observed macroscopically in real time by the dramatic colour change.

`MnO_4^(-) + 8H^(+) + 5e^(-) rarr Mn^(2+) + 4H_2O`

Is this balanced with respect to mass and charge? Don't trust my arithmetic.