Chemical Education Today
Letters Literature Cited
Potassium Permanganate Hazards 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 I2 + 2e
᎑
Reducing Agent ᎑
Reduction Potential/ V
2I
+0.53
Br2 + 2e᎑
2Br᎑
+1.07
Cl2 + 2e᎑
2Cl᎑
+1.36
MnO4᎑ + 8H+ + 5e᎑
Mn2+ + 4H2O
+1.49
᎑
F 2 + 2e
᎑
2F
+2.87
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.
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1. Young, J. A. J. Chem. Educ. 2003, 80, 873. Vladimir M. Petrusevski Institute of Chem., Faculty of Nat. Sci. and Mathematics Univerzitet “Sv. Kiril i Metodij” Republic of Macedonia
[email protected] The author replies As one who has a deep interest in promoting the safe use of chemicals, I am pleased to note that people are reading, and reading carefully, the Chemical Laboratory Information Profiles (CLIPs) now being published in this Journal. It is also a distinct pleasure for an old, retired physical chemistry professor to have an opportunity to teach a bit of physical chemistry to an articulate and, I daresay, a concerned, colleague. Briefly put, the conclusion drawn by Petrusevski to the effect that potassium permanganate will not react with hydrofluoric acid is correct if the concentrations of the two reagents are such that these reagents are at unit activity, their temperature is 25 °C, and they are under a pressure of one atmosphere, and so on and so forth. However, if the above conditions are not met, there may, or may not, depending upon the details, be a reaction between these two chemicals. For details describing a reaction, somewhat violent in nature, between potassium permanganate and a concentrated solution of hydrofluoric acid see ref 1. Literature Cited 1. Black, A. M. et al. J. Chem. Soc., Dalton Trans. 1974, 977. Jay A. Young
JCE Feature Editor Chemical Laboratory Information Profiles (CLIPs) 12916 Allerton Lane Silver Spring, MD 20904-3105
Vol. 81 No. 7 July 2004
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Journal of Chemical Education
951
