Question

How does oxidation state affect color?

Answer 1

There is no necessary relationship.........

Explanation:

There is no necessary relationship.........but generally the metal ions in the higher oxidation states, i.e. `Cr(VI+)` in `Cr_2O_7^(2-)` `Mn(VII+)` in `MnO_4^(-)` tend to be strongly coloured. Since the metal centre is totally oxidized these are charge-transfer bands, which are spin-allowed and intense.

THe redox couple of permanganate to `Mn^(2+)`..........

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

....is highly useful for redox titrations, in that while `MnO_4^-` is a strong, intense purple...........

.........its oxidation product `Mn^(2+)` is a high-spin `d^5` system, which is, to all intents and purposes, COLOURLESS in aqueous solution.

For an example of how this might be used in a problem see here.