What color is permanganate ion?

1 Answer
Jun 3, 2017

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

https://img1.exportersindia.com/


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.