Question

What color is permanganate ion?

Answer 1

Permanganate, `"MnO"_4^(-)`, is purple.

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

• `"Cl"^(-)` can be oxidized into `"Cl"_2`, but it tends to take some heating. The light pink goes away when `"MnO"_4^(-)` gets reduced to `"Mn"^(2+)`.

`10"Cl"^(-)(aq) + 16"H"^(+)(aq) + 2"MnO"_4^(-)(aq) -> 5"Cl"_2(l) + 2"Mn"^(2+)(aq) + 8"H"_2"O"(l)`

• `"Br"^(-)` can be oxidized to `"Br"_2`, which turns the solution a clear yellow (while the permanganate color disappears).

`10"Br"^(-)(aq) + 16"H"^(+)(aq) + 2"MnO"_4^(-)(aq) -> 5"Br"_2(l) + 2"Mn"^(2+)(aq) + 8"H"_2"O"(l)`

• `"I"^(-)` gets oxidized to `"I"_2` even more easily, and becomes a dark yellow, somewhat brown, clear color (while the permanganate color disappears).

`10"I"^(-)(aq) + 16"H"^(+)(aq) + 2"MnO"_4^(-)(aq) -> 5"I"_2(l) + 2"Mn"^(2+)(aq) + 8"H"_2"O"(l)`

Based on what I've just described, how can you order the halides in terms of least to most positive `E_"red"^@` (i.e. which `E_(o x)^@` is the most negative/which halide is most easily oxidized)? Check your work with a standard reduction table.