Perxenate solutions

The perxenates are colorless, thermally stable solids. Anhydrous sodium perxenate can be obtained at 373 K. It decomposes at 633 K. The corresponding barium salt decomposes at about 570 K. Perxenate solutions are powerful and rapid oxidizing agents. Xenon(VIII) is reduced to xenon(VI). Oxidation processes in acid media are more effective, but they must be fast enough to compete with decomposition of the perxenate, which is also rapid in acid. 

Aqueous Xevin arises, not only in the above disproportionation, but also when ozone is passed through a dilute solution of Xevl in base. These yellow perxenate solutions are powerful and rapid oxidizing agents. 

The aeid potential is exeeeded only by fluorine (p. 804), perxenate (p. 901), atomie O, the OH radieal, and a few other sueh potent oxidants. Deeomposition is rapid in aeid solutions but the allotrope is much more stable in alkaline solution. At 25° the half-life of O3 in 1 M NaOH is 2min eorresponding times for 5 m and 20 m NaOH are 40 min and 83 h respeetively. 

However, although some salts have been isolated, alkaline solutions are not stable and immediately, if slowly, begin to disproportionate into Xe (perxenates) and Xe gas by routes such as ... 

As mentioned above, xenon trioxide is an endothermic compound which explodes violently at the slightest provocation. Aqueous solutions are stable but powerfully oxidizing. These solutions are weakly acidic ( xenic acid ) and contain molecular XeOj When these solutions are made basic. HXeO ions are formed and alkali hydrogen xenates, MHXe04, may be isolated from them. Hydrogen xenale ions disproportionate in alkaline solution to yield perxenates ... 

Xenate solutions may also be oxidized directly to perxenate with ozone. Solid perxenates are rather insoluble and are unusually stable for xenon-oxygen compounds Most do not decompose until healed above 200 eC. X-ray crystallographic structures have been determined for several perxenates. and they have been found to contain the octahedral XeC ion. which persists in aqueous solution (possibly with proionation to HXeOj"). 

In acid solution 03 is exceeded in oxidizing power only by fluorine, the perxenate ion, atomic oxygen, OH radicals, and a few other such species. The rate of decomposition of ozone drops sharply in alkaline solutions, the half-life being 2 min in 1 M NaOH at 25°C, 40 min at 5 M, and 83 h at 20 M ... 

Solutions of perxenates are reduced by water at pH 11.5 at a rate of l%/h, but in acid solutions almost instantaneously ... 

Hydrolysis of xenon hexafluoride or tetrafluoride with a sodium hydroxide solution results in the precipitation of a stable xenon (VIII) salt, sodium perxenate, Na4XeOe, which on heating does not decompose until around 300°. Similar hydrolysis with potassium hydroxide can yield a yellow precipitate which is a mixed potassium perxenate-xenon trioxide salt, and is explosive even when damp. With more concentrated base, the much more stable hydrated perxenate may be isolated. 

Xenon hexafluoride hydrolyzes in excess dilute acid or water to produce XeOa [Xe(VI)] in solution. Hydrolysis with strong base results in the precipitation of a perxenate salt [Xe(VIlI)]. Xenon hexafluoride is a fairly strong fluorinating agent, and it forms addition compounds w ith other fluorides such as BF3, AsFs, SbFs, and alkali metal fluorides. 

Sodium perxenate is stable at room temperature, but if left exposed to the air, it may absorb water and carbon dioxide. The salt is soluble in water to the extent of about 0.025 M, and the solutions are basic because of hydrolysis ... 

Solutions of sodium perxenate are very powerful oxidants, and accidental contact with reducing substances should be avoided. A frequent reaction product is xenon trioxide, the hazards of which are detailed in the preceding s Oithesis. ... 

Determination of the total oxidizing power gives the amount of Xe(VIII) and may best be effected by dissolving the perxenate in a sodium iodide solution, acidifying with dilute perchloric or sulfuric acid, and titrating the liberated triiodide with thiosulfate. The reaction proceeds according to the overall stoichiometry ... 

Sodium perxenate, first prepared in 1963, has a standard electrode potential estimated to be 3.0 V in acid solution. Without a catalyst and at room temperature it rapidly oxidizes Mn(II) to Mn(VII). In neutral solution it oxidizes Np(IV) and Pu(IV) hydroxides to Np(VI) and Pu(VI). Sodium perxenate decomposes in acid solution ... 

The perxenate ion is an even more powerful oxidizing agent than Xe03 and is capable of oxidizing Mn to permanganate, Mn04 in acidic solution. 

Write a balanced equation for the oxidation of Mn to Mn04 by the perxenate ion in acidic solution (assume that neutral Xe is formed). 

The Am(VII) solid compound had been synthesized by interaction of a Am(VI) perxenate complex with ozone in the solid phase at room temperature. The spectrum contains maxima at 712 and 750 nm is the same as the spectrum of the -50% mixture of Am(VII) and Am(VI) species, prepared a the 3.5M NaOH solution [89]. The generalities of the spectrum of the solid Am precipitate obtained in our work are very much like the spectra of Np(VII) in alkaline solutions, but are shifted to the long wave range. The Am(VII) compound is unstable even in the solid state under an oxygen atmosphere and decomposes during 30 min at room temperature. In alkaline solutions, Am(VII) is reduced faster than Pu(VII). 

The trioxide is the anhydride ofxenic acid, H2Xe04. In aqueous basic solution, the acid forms the hydrogen xenate ion, HXe04", which further disproportionates to the perxenate ion, XeOe, in which xenon attains its highest oxidation number of +8. 

Xenates contain Xe (+ VI) and they slowly disproportionate in solution to perxenates (which contain Xe (+ VIII) and Xe... 

A normal-co-ordinate treatment of Xe02F2 using a modified Urey-Bradley force field has been carried out and the results have been compared with new treatments for XeOp4 and Xe03p2, as well as with force constants reported for other xenon compounds.The results have been set out in Table 2, from which it is evident that, as oxygen atoms are added to Xep2, the Xe—F bond distance decreases while the Xe—O bond distance increases. Aqueous solutions of pure XeOs at concentrations up to 0.1 mol T can be prepared from sodium perxenate by means of a cation-exchange resin. 

On page 834, the statement is made Hydrogen xenate ions disproportionate in alkaline solution to yield perxenates. .. Can you confirm this assertion based on the Latimer diagrams for xenon ... 

The addition of alkali to Xe03 solutions yields xenate ions [HXeOJ. Although salts of this species can be isolated, solutions containing [HXe04] disproportionate to give the perxenate ion, [Xe06]4", and xenon ... 

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