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In the August 2003 issue of this Journal, one may find some data concerning hazards when working with KMnO4, given in the Chemical Laboratory Information Profile prepared by Young (1). Among many useful and relevant data and warnings, there are two points that are incorrect. KMnO4 is said to be incompatible with “…concentrated acids such as HCl, HF, H2SO4, and others.” One paragraph lower (in the section Reactivity Hazards) one also reads that “Potassium permanganate reacts violently with…hydrogen halides…”. HF, it must be said, is not incompatible with KMnO4, as may be witnessed by the redox potentials of the corresponding half-reactions. Oxidizing Agent | Reducing Agent | Reduction Potential/ V |
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I2 + 2e– | 2I– | +0.53 | Br2 + 2e– | 2Br– | +1.07 | Cl2 + 2e– | 2Cl– | +1.36 | MnO4– + 8H+ +5e– | Mn2+ + 4H2O | +1.49 | F2 + 2e– | 2F– | +2.87 |
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Fluoride ions, alas, cannot be oxidized by MnO4–, or, for that matter, by any other chemical reagent. I have tried this (in my early years as a student) and, of course, nothing particularly happened. KMnO4 simply dissolved in the water containing HF. Electrolysis is the only practical method for generating gaseous fluorine. So, HF must be dropped from the list of incompatible chemicals. In this sense, in the second paragraph of the Reactivity Hazards, it would be better to put explicitly HCl, HBr, HI, instead of “hydrogen halides”, since the last means all of the halides, which is not true, as demonstrated above. Literature Cited- Young, J. A. J. Chem. Educ. 2003, 80, 873.
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