Perxenate
Encyclopedia
In chemistry
, perxenates are salts of the yellow xenon
-containing anion . This anion has octahedral molecular geometry
, as determined by Raman spectroscopy
, having O–Xe–O bond angles varying between 87° and 93°. The Xe–O bond length was determined by X-ray spectroscopy to be 1.875 Å.
of xenon trioxide
when dissolved in strong alkali:
When
is used as the alkali, barium perxenate can be crystallized from the resulting solution.
in water. It has not been isolated as a free acid, because under acidic conditions it rapidly decomposes into xenon trioxide
and oxygen
gas:
Its extrapolated formula, , is inferred from the octahedral geometry
of the perxenate ion in its alkali metal
salts.
The pH
of aqueous perxenic acid, (pK), has been indirectly calculated to be < 0, making it a very strong acid. Its first ionization yields , which has a pK value of 4.29, still relatively acidic. The twice deprotonated species has a pK value of 10.81. Due to its rapid decomposition under acidic conditions as described above, however, it is most commonly encountered as perxenate salts, bearing the anion .
s, capable of oxidising silver(I) to silver(III), copper(II) to copper(III), and to . The perxenate anion is unstable in acidic solutions, being almost instantaneously reduced to HXeO.
The sodium
, potassium
, and barium
salts are soluble. Barium perxenate solution is used as starting material for the synthesis of xenon tetroxide
(XeO4) by mixing it with concentrated sulfuric acid
:
Most metal perxenates are stable, except silver perxenate, which decomposes violently.
from curium
. The separation involves the oxidation of to by sodium perxenate in acidic solution in the presence of , followed by treatment with calcium fluoride, which forms insoluble fluorides with and , but retains and in solution as soluble fluorides.
Chemistry
Chemistry is the science of matter, especially its chemical reactions, but also its composition, structure and properties. Chemistry is concerned with atoms and their interactions with other atoms, and particularly with the properties of chemical bonds....
, perxenates are salts of the yellow xenon
Xenon
Xenon is a chemical element with the symbol Xe and atomic number 54. The element name is pronounced or . A colorless, heavy, odorless noble gas, xenon occurs in the Earth's atmosphere in trace amounts...
-containing anion . This anion has octahedral molecular geometry
Octahedral molecular geometry
In chemistry, octahedral molecular geometry describes the shape of compounds where in six atoms or groups of atoms or ligands are symmetrically arranged around a central atom, defining the vertices of an octahedron...
, as determined by Raman spectroscopy
Raman spectroscopy
Raman spectroscopy is a spectroscopic technique used to study vibrational, rotational, and other low-frequency modes in a system.It relies on inelastic scattering, or Raman scattering, of monochromatic light, usually from a laser in the visible, near infrared, or near ultraviolet range...
, having O–Xe–O bond angles varying between 87° and 93°. The Xe–O bond length was determined by X-ray spectroscopy to be 1.875 Å.
Synthesis
Perxenates are synthesized by the disproportionationDisproportionation
Disproportionation, also known as dismutation is used to describe a specific type of redox reaction in which a species is simultaneously reduced and oxidized so as to form two different products....
of xenon trioxide
Xenon trioxide
Xenon trioxide is an unstable compound of xenon in its +6 oxidation state. It is a very powerful oxidizing agent, and liberates oxygen from water slowly , accelerated by exposure to sunlight. It is dangerously explosive upon contact with organic materials...
when dissolved in strong alkali:
- 2 (s) + 4 (aq) → Xe (g) + (aq) + (g) + 2 (l)
When
Barium hydroxide
Barium hydroxide is the chemical compound with the formula Ba2. Also known as baryta, it is one of the principal compounds of barium. The white granular monohydrate is the usual commercial form.-Preparation:...
is used as the alkali, barium perxenate can be crystallized from the resulting solution.
Perxenic acid
Perxenic acid is the unstable conjugate acid of the perxenate anion, formed by the solution of xenon tetroxideXenon tetroxide
Xenon tetroxide is a chemical compound of xenon and oxygen with molecular formula XeO4, remarkable for being a relatively stable compound of a noble gas...
in water. It has not been isolated as a free acid, because under acidic conditions it rapidly decomposes into xenon trioxide
Xenon trioxide
Xenon trioxide is an unstable compound of xenon in its +6 oxidation state. It is a very powerful oxidizing agent, and liberates oxygen from water slowly , accelerated by exposure to sunlight. It is dangerously explosive upon contact with organic materials...
and oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
gas:
- 2 + 6 → 2 + 4 +
Its extrapolated formula, , is inferred from the octahedral geometry
Octahedral molecular geometry
In chemistry, octahedral molecular geometry describes the shape of compounds where in six atoms or groups of atoms or ligands are symmetrically arranged around a central atom, defining the vertices of an octahedron...
of the perxenate ion in its alkali metal
Alkali metal
The alkali metals are a series of chemical elements in the periodic table. In the modern IUPAC nomenclature, the alkali metals comprise the group 1 elements, along with hydrogen. The alkali metals are lithium , sodium , potassium , rubidium , caesium , and francium...
salts.
The pH
PH
In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...
of aqueous perxenic acid, (pK), has been indirectly calculated to be < 0, making it a very strong acid. Its first ionization yields , which has a pK value of 4.29, still relatively acidic. The twice deprotonated species has a pK value of 10.81. Due to its rapid decomposition under acidic conditions as described above, however, it is most commonly encountered as perxenate salts, bearing the anion .
Properties
Perxenic acid and the anion XeO are both strong oxidizing agentOxidizing agent
An oxidizing agent can be defined as a substance that removes electrons from another reactant in a redox chemical reaction...
s, capable of oxidising silver(I) to silver(III), copper(II) to copper(III), and to . The perxenate anion is unstable in acidic solutions, being almost instantaneously reduced to HXeO.
The sodium
Sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...
, potassium
Potassium
Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...
, and barium
Barium
Barium is a chemical element with the symbol Ba and atomic number 56. It is the fifth element in Group 2, a soft silvery metallic alkaline earth metal. Barium is never found in nature in its pure form due to its reactivity with air. Its oxide is historically known as baryta but it reacts with...
salts are soluble. Barium perxenate solution is used as starting material for the synthesis of xenon tetroxide
Xenon tetroxide
Xenon tetroxide is a chemical compound of xenon and oxygen with molecular formula XeO4, remarkable for being a relatively stable compound of a noble gas...
(XeO4) by mixing it with concentrated sulfuric acid
Sulfuric acid
Sulfuric acid is a strong mineral acid with the molecular formula . Its historical name is oil of vitriol. Pure sulfuric acid is a highly corrosive, colorless, viscous liquid. The salts of sulfuric acid are called sulfates...
:
- Ba2XeO6 (s) + 2 H2SO4 (aq) → H4XeO6 (aq) + 2 BaSO4 (s)
Most metal perxenates are stable, except silver perxenate, which decomposes violently.
Applications
Sodium perxenate, , can be used for the analytic separation of trace amounts of americiumAmericium
Americium is a synthetic element that has the symbol Am and atomic number 95. This transuranic element of the actinide series is located in the periodic table below the lanthanide element europium, and thus by analogy was named after another continent, America.Americium was first produced in 1944...
from curium
Curium
Curium is a synthetic chemical element with the symbol Cm and atomic number 96. This radioactive transuranic element of the actinide series was named after Marie Skłodowska-Curie and her husband Pierre Curie. Curium was first intentionally produced and identified in summer 1944 by the group of...
. The separation involves the oxidation of to by sodium perxenate in acidic solution in the presence of , followed by treatment with calcium fluoride, which forms insoluble fluorides with and , but retains and in solution as soluble fluorides.