# How does oxidation state affect color?

Jun 13, 2017

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

#### Explanation:

There is no necessary relationship.........but generally the metal ions in the higher oxidation states, i.e. $C r \left(V I +\right)$ in $C {r}_{2} {O}_{7}^{2 -}$ $M n \left(V I I +\right)$ in $M n {O}_{4}^{-}$ 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 $M {n}^{2 +}$..........

$M n {O}_{4}^{-} + 8 {H}^{+} + 5 {e}^{-} \rightarrow M {n}^{2 +} + 4 {H}_{2} O$

....is highly useful for redox titrations, in that while $M n {O}_{4}^{-}$ is a strong, intense purple...........

.........its oxidation product $M {n}^{2 +}$ 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.