Why does KMnO4 react with KBr and KI but not KCl?

[dajugganaut]

Hi all,

The other day in chemistry class, we carried out several different redox reactions. In one set of the experiments, we reacted potassium permanganate with 3 different potassium halides (KCl, KBr, KI). this particular redox reaction also requires an acidic environment, so sulfuric acid was added.

Some of my friends believe that they saw KBr and KI react with potassium permanganate, but not KCl. I'm looking over the equations for each of the reaction and I can't figure out why KBr and KI would react but not KCl (furthermore, I can't even be sure that KBr and KI reacted at all.)

Does anyone have any ideas?

[ The ON for Mn is 7+ in potassium permanganate. This is the maximum ON for Mn. So naturally, I thought that all reactions would proceed, as bromide, chloride and iodide ions are not at their maximum ON ]

 

[member 553083]

The reason why KCl did not react with potassium permanganate is because the chloride ion does not have a high enough oxidation number to be oxidized by potassium permanganate. The oxidation number of chlorine in KCl is -1, which is too low for it to be oxidized. Bromide and iodide ions, however, have oxidation numbers of +1 and +7 respectively, which are high enough for them to be oxidized. That is why the reaction proceeded with bromide and iodide ions, but not with chloride ions.