Why are containers of potassium permanganate covered with aluminum foil?
Tuesday, August 3rd, 2010 at
12:11 AM
When in use in a Chemistry Lab, why are containers of potassium permanganate covered with aluminum foil?
Filed under: Potassium Questions
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Let me take an (educated I hope!) guess. KMnO4 strongly absorbs in the visible region (I can’t think of a cmpd that has a stronger molar absorbtivity). The absorption is not a d-d transition as Mn in [MnO4]^- is formally Mn(VII) or d^0. It is due to a LMCT (ligand to metal charge transfer) that is strongly allowed. It takes an electron in a lone pair on oxygen and puts it into an empty Mn d AO. It essentially reduces Mn(VII) to Mn(VI) so prolonged exposure of KMnO4 to visible light will reduce Mn probably to brown MnO2 (Mn(IV) which of course will make the KMnO4 useless as a primary standard for redox analytical chem so it is wrapped in Al foil to keep ALL visible light away from it. Most light sensitive cmpds are stored in brown bottles that keep the high energy blue and UV out, but that evidently this is not sufficient for potassium permanganate.