# What color is permanganate ion?

Jun 3, 2017

Permanganate, ${\text{MnO}}_{4}^{-}$, is purple.

It can make for a very colorful laboratory exercise. Take a sample of $\text{NaCl}$, $\text{NaBr}$, and $\text{NaI}$, and make separate aqueous solutions of them. Of these... in acidic solution:

• ${\text{Cl}}^{-}$ can be oxidized into ${\text{Cl}}_{2}$, but it tends to take some heating. The light pink goes away when ${\text{MnO}}_{4}^{-}$ gets reduced to ${\text{Mn}}^{2 +}$.

$10 \text{Cl"^(-)(aq) + 16"H"^(+)(aq) + 2"MnO"_4^(-)(aq) -> 5"Cl"_2(l) + 2"Mn"^(2+)(aq) + 8"H"_2"O} \left(l\right)$

• ${\text{Br}}^{-}$ can be oxidized to ${\text{Br}}_{2}$, which turns the solution a clear yellow (while the permanganate color disappears).

$10 \text{Br"^(-)(aq) + 16"H"^(+)(aq) + 2"MnO"_4^(-)(aq) -> 5"Br"_2(l) + 2"Mn"^(2+)(aq) + 8"H"_2"O} \left(l\right)$

• ${\text{I}}^{-}$ gets oxidized to ${\text{I}}_{2}$ even more easily, and becomes a dark yellow, somewhat brown, clear color (while the permanganate color disappears).

$10 \text{I"^(-)(aq) + 16"H"^(+)(aq) + 2"MnO"_4^(-)(aq) -> 5"I"_2(l) + 2"Mn"^(2+)(aq) + 8"H"_2"O} \left(l\right)$

Based on what I've just described, how can you order the halides in terms of least to most positive ${E}_{\text{red}}^{\circ}$ (i.e. which ${E}_{o x}^{\circ}$ is the most negative/which halide is most easily oxidized)? Check your work with a standard reduction table.