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Perxenic acid is the unstable conjugate acid of the perxenate anion, formed by the solution of xenon tetroxide in water. It has not been isolated as a free acid, because under acidic conditions it rapidly decomposes into xenon trioxide and oxygen gas:
The pKa of aqueous perxenic acid has been indirectly calculated to be below 0, making it an extremely strong acid. Its first ionization yields the anion , which has a pKa value of 4.29, still relatively acidic. The twice deprotonated species has a pKa value of 10.81. Due to its rapid decomposition under acidic conditions as described above, however, it is most commonly known as perxenate salts, bearing the anion .
Perxenic acid and the anion are both strong oxidizing agents, capable of oxidising silver(I) to silver(III), copper(II) to copper(III), and manganese(II) to permanganate. The perxenate anion is unstable in acidic solutions, being almost instantaneously reduced to .
Ba2XeO6 (s) + 2 H2SO4 (l) -> XeO4 (g) + 2 BaSO4 (s) + 2 H2O (l)
Most metal perxenates are stable, except silver perxenate, which decomposes violently.
Sodium perxenate, Na4XeO6, can be used for the analytic separation of trace amounts of americium from curium. The separation involves the oxidation of Am3+ to Am4+ by sodium perxenate in acidic solution in the presence of La3+, followed by treatment with calcium fluoride, which forms insoluble fluorides with Cm3+ and La3+, but retains Am4+ and Pu4+ in solution as soluble fluorides.
^ abHolleman, Arnold Frederik; Wiberg, Egon (2001), Wiberg, Nils (ed.), Inorganic Chemistry, translated by Eagleson, Mary; Brewer, William, San Diego/Berlin: Academic Press/De Gruyter, p. 399, ISBN0-12-352651-5
^Peterson, J. L.; Claassen, H. H.; Appelman, E. H. (March 1970). "Vibrational spectra and structures of xenate(VI) and perxenate(VIII) ions in aqueous solution". Inorganic Chemistry. 9 (3): 619-621. doi:10.1021/ic50085a037.
^ abHarding, Charlie; Johnson, David Arthur; Janes, Rob (2002). Elements of the p Block. Molecular World. 9. Royal Society of Chemistry. p. 93. ISBN0-85404-690-9.
^ abcKlaening, U. K.; Appelman, E. H. (October 1988). "Protolytic properties of perxenic acid". Inorganic Chemistry. 27 (21): 3760-3762. doi:10.1021/ic00294a018.
^Holleman, Arnold Frederik; Wiberg, Egon (2001), Wiberg, Nils (ed.), Inorganic Chemistry, translated by Eagleson, Mary; Brewer, William, San Diego/Berlin: Academic Press/De Gruyter, p. 400, ISBN0-12-352651-5
^John H. Holloway; Eric G. Hope (1998). A. G. Sykes (ed.). Advances in Inorganic Chemistry. 46. Academic Press. p. 67. ISBN0-12-023646-X.
^ abHolcomb, H. P. (March 1965). "Analytical Oxidation of Americium with Sodium Perxenate". Analytical Chemistry. 37 (3): 415. doi:10.1021/ac60222a002.