A sulfite sulfate is a
chemical compound
A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one ele ...
that contains both
sulfite
Sulfites or sulphites are compounds that contain the sulfite ion (or the sulfate(IV) ion, from its correct systematic name), . The sulfite ion is the conjugate base of bisulfite. Although its acid (sulfurous acid) is elusive, its salts are wide ...
and
sulfate
The sulfate or sulphate ion is a polyatomic ion, polyatomic anion with the empirical formula . Salts, acid derivatives, and peroxides of sulfate are widely used in industry. Sulfates occur widely in everyday life. Sulfates are salt (chemistry), ...
anion
An ion () is an atom or molecule with a net electrical charge.
The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conve ...
s
3">O3sup>2−
4">O4sup>2−. These compounds were discovered in the 1980s as
calcium
Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar t ...
and
rare earth element
The rare-earth elements (REE), also called the rare-earth metals or (in context) rare-earth oxides or sometimes the lanthanides ( yttrium and scandium are usually included as rare earths), are a set of 17 nearly-indistinguishable lustrous si ...
salts. Minerals in this class were later discovered. Minerals may have sulfite as an essential component, or have it substituted for another anion as in
alloriite
Alloriite is a silicate mineral that belongs to the cancrinite group, or more specifically the feldspathoid group. It is currently only found in Italy. It was discovered by and named for the Italian mineralogist Roberto Allori, an avid mineral col ...
. The related ions
3SOSO2">3SOSO2sup>2− and
2SO)2SO2">O2SO)2SO2sup>2− may be produced in a reaction between sulfur dioxide and sulfate and exist in the solid form as tetramethyl ammonium salts. They have a significant partial pressure of sulfur dioxide.
Related compounds are
selenate selenite
A selenate selenite is a chemical compound or salt that contains selenite and selenate anions (SeO32- and SeO42-). These are mixed anion compounds. Some have third anions.
Naming
A selenate selenite compound may also be called a selenite selen ...
s and
tellurate tellurite
A tellurite tellurate is chemical compound or salt that contains tellurite and tellurate anions eO3sup>2- eO4 sup>2-. These are mixed anion compounds, meaning the compounds are cations that contain one or more anions. Some have third anions. Envi ...
s with a varying chalcogen. They can be classed as mixed valent compounds.
Production
Europium and cerium rare earth sulfite sulfates are produced when heating the metal sulfite trihydrate in air.
Ce
2(SO
3)
3.3H
2O + O
2 → Ce
2(SO
3)
2SO
4 + 3H
2O
Ce
2(SO
3)
3.3H
2O + O
2 → Ce
2SO
3(SO
4)
2 + 3H
2O
Other rare earth sulfite sulfates can be crystallized as hydrates from a water solution.
These sulfite sulfates can be made by at least three methods. One is to dissolve a rare earth
oxosulfate in water and then bubble in
sulfur dioxide
Sulfur dioxide ( IUPAC-recommended spelling) or sulphur dioxide (traditional Commonwealth English) is the chemical compound with the formula . It is a toxic gas responsible for the odor of burnt matches. It is released naturally by volcanic ...
. The second way a rare earth oxide is dissolved in a half equivalent of
sulfuric acid. The third way was to bubble sulfur dioxide through a suspension of rare earth oxide in water until it dissolved, then let it sit around for a few days with limited air exposure. To make calcium sulfite sulfate, a soluble calcium salt is added to a mixed solution of
sodium sulfite
Sodium sulfite (sodium sulphite) is the inorganic compound with the chemical formula Na2 SO3. A white, water-soluble solid, it is used commercially as an antioxidant and preservative. A heptahydrate is also known but it is less useful because of ...
and
sodium sulfate
Sodium sulfate (also known as sodium sulphate or sulfate of soda) is the inorganic compound with formula Na2SO4 as well as several related hydrates. All forms are white solids that are highly soluble in water. With an annual production of 6 mill ...
.
Control of pH is important when attempting to produce solid sulfite compounds. In basic conditions sulfite easily oxidises to sulfate and in acidic conditions it easily turns into sulfur dioxide.
Properties
In the sulfite sulfates, sulfur has both a +4 and a +6
oxidation state
In chemistry, the oxidation state, or oxidation number, is the hypothetical charge of an atom if all of its bonds to different atoms were fully ionic. It describes the degree of oxidation (loss of electrons) of an atom in a chemical compound. ...
.
The crystal structure of sulfite sulfates has been difficult to study, as the crystal symmetry is low, crystals are usually microscopic as they are quite insoluble, and they are mixed with other related phases. So they have been studied via
powder X-ray diffraction.
Reactions
When heated in the absence of oxygen, cerium sulfite sulfate hydrate parts with water by 400 °C. Up to 800° it loses some sulfur dioxide. From 800° to 850 °C it loses sulfur dioxide and
disulfur
Disulfur is the diatomic molecule with the formula S2. It is analogous to the dioxygen molecule but rarely occurs at room temperature. This violet gas is the dominant species in hot sulfur vapors. S2 is one of the minor components of the atmos ...
resulting in cerium oxy disulfate, and dioxy sulfate, which loses some further sulfur dioxide as it is heated to 1000 °C. Over 1000° the remaining oxysulfates decompose to sulfur dioxide, oxygen and cerium dioxide. This reaction is studied as a way to convert sulfur dioxide into sulfur and oxygen using only heat.
Another thermochemical reaction for cerium sulfite sulfate hydrate involves using iodine to oxidise the sulfite to sulfate, producing
hydrogen iodide
Hydrogen iodide () is a diatomic molecule and hydrogen halide. Aqueous solutions of HI are known as hydroiodic acid or hydriodic acid, a strong acid. Hydrogen iodide and hydroiodic acid are, however, different in that the former is a gas under s ...
which can then be used to make hydrogen gas and iodine. When combined with the previous high temperature process, water can be split into oxygen and hydrogen using heat only. This is termed the GA sulfur-iodine
water splitting
Water splitting is the chemical reaction in which water is broken down into oxygen and hydrogen:
:2 H2O → 2 H2 + O2
Efficient and economical water splitting would be a technological breakthrough that could underpin a hydrogen economy, bas ...
cycle.
Applications
Calcium sulfite sulfate hydrate is formed in flue gas scrubbers that attempt to remove sulfur dioxide from coal burning facilities. Calcium sulfite sulfate hydrate is also formed in the weathering of limestone, concrete and mortar by sulfur dioxide polluted air. These two would be classed as anthropogenic production as it was not deliberately produced or used.
List
References
{{Reflist
Sulfites
Sulfates
Mixed anion compounds