|Jmol-3D images||Image 1|
|Molar mass||233.43 g/mol|
1600 °C (decomp)
|Solubility in water|| 0.0002448 g/100 mL (20 °C) |
0.000285 g/100 mL (30 °C)
|Solubility product, Ksp||1.0842 × 10-10 (25 °C)|
|Solubility||insoluble in alcohol, soluble in concentrated sulfuric acid|
|Refractive index (nD)||1.64|
| Std enthalpy of
| Standard molar
|EU classification||not listed|
| (what is: / ?) |
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Barium sulfate is the inorganic compound with the chemical formula BaSO4. It is a white crystalline solid that is odorless and insoluble in water. It occurs as the mineral barite, which is the main commercial source of barium and materials prepared from it. The white opaque appearance and its high density are exploited in its main applications.
Almost all of the barium consumed commercially is obtained from the mineral barite, which is often highly impure. Barite is processed by carbothermal reduction (heating with coke) to give barium sulphide:
- BaSO4 + 4 C → BaS + 4 CO
In contrast to barium sulfate, barium sulfide is soluble in water and readily converted to the oxide, carbonate, and halides. To produce highly pure barium sulfate, the sulfide or chloride is treated with sulfuric acid or sulfate salts:
- BaS + H2SO4 → BaSO4 + H2S
Barium sulfate produced in this way is often called blanc fixe, which is French for "permanent white." Blanc fixe is the form of barium encountered in consumer products, such as paints.
In the laboratory barium sulfate is generated by combining solutions of barium ions and sulfate salts. Because barium sulfate is the least toxic salt of barium due to its insolubility, wastes containing barium salts are sometimes treated with sodium sulfate to immobilize (detoxify) the barium. Barium sulfate is one of the most insoluble salts of sulfate. Its low solubility is exploited in qualitative inorganic analysis as a test for Ba2+ ions as well as for sulfate.
The majority of synthetic barium sulfate is used as a component of white pigment for paints. In oil paint, barium sulfate is almost transparent,and is used as a filler or to modify consistency. One major manufacturer of artists' oil paint sells "permanent white" that contains a mixture of titanium white pigment (TiO2) and barium sulfate. The combination of barium sulfate and zinc sulfide (ZnS) is the inorganic pigment called lithopone. In photography it is used as a coating for certain photographic papers.
Barium sulfate is frequently used clinically as a radiocontrast agent for X-ray imaging and other diagnostic procedures. It is most often used in imaging of the GI tract during what is colloquially known as a 'barium meal'. It is administered, orally or by enema, as a suspension of fine particles in an aqueous solution (often with sweetening agents added). Although barium is a heavy metal, and its water-soluble compounds are often highly toxic, the low solubility of barium sulfate protects the patient from absorbing harmful amounts of the metal. Barium sulfate is also readily removed from the body, unlike Thorotrast, which it replaced. Due to the relatively high atomic number (Z = 56) of barium, its compounds absorb X-rays more strongly than compounds derived from lighter nuclei.
Barium sulfate is also used during the procedure of the soil pH test. In this test it is used so that it precipitates out any particles (usually clay particles) that would otherwise 'cloud' solution preventing one from seeing the colour of the pH indicator i.e. the result of the test. It is also used in Episal salt, brake linings, anacoustic foams, powder coatings, and root canal filling.
In metal casting, the moulds used are often coated with barium sulfate in order to prevent the molten metal from bonding with the mould.
Barium sulfate is a low surface area material used as a support for selectively hydrogenating functional groups sensitive to overreduction. With a low surface area, the contact time of the substrate with the catalyst is shorter. A supported palladium catalyst on barium sulfate, and doped (poisoned) with quinoline hydrogenates alkynes into cis-alkenes. The quinoline and the special support prevent overreduction to the alkane.
As barium compounds emit a green light when burned, barium salts are often used in green pyrotechnic formulas, but the nitrate and chlorate salts are more common. Barium sulfate is commonly used as a component of "strobe" pyrotechnic compositions.
As barium sulfate has high burning point and is insoluble in water, it is used as a coating material in casting of copper anode plates. The anode plates are cast in copper molds, so to avoid the contact of the liquid copper and the solid copper mold, a solution of barium sulfate in water is used as a coating material on the mold surface. Thus when the liquid copper solidifies in form of an anode plate it can be easily removed from its mold.
Barium sulfate is reduced to barium sulfide by carbon. The accidental discovery of this conversion many centuries ago led to the discovery of the first synthetic phosphor (Hollman and Wiberg, 2001). The sulfide, unlike the sulfate, is water soluble. Sometime prior to the autumn of 1803, the Englishman John Dalton was able to explain the results of some of his studies by assuming that matter is composed of atoms and that all samples of any given compound consist of the same combination of these atoms. Dalton also noted that in series of compounds, the ratios of the masses of the second element that combine with a given weight of the first element can be reduced to small whole numbers (the law of multiple proportions). This was further evidence for atoms. Dalton's theory of atoms was published by Thomas Thomson in the 3rd edition of his System of Chemistry in 1807 and in a paper about strontium oxalates published in the Philosophical Transactions. Dalton published these ideas himself in the following year in the New System of Chemical Philosophy. The symbol used by Dalton for barium is shown below. [See History of Chemistry, Sir Edward Thorpe, volume 1, Watts & Co, London, 1914.]
During the early part of the 20th century, during the Japanese colonization period, hokutolite was found to exist naturally in the Beitou hot-springs area near Taipei City, Taiwan. Hokutolite is a radioactive mineral composed mostly of PbSO4 and BaSO4, but also containing traces of U, Th and Ra.2 The Japanese harvested these elements for industrial uses, and also developed dozens of “therapeutic hot-spring baths” in the area.
Barium, 1808, Mod.L., from Gk. barys "heavy;" so called by its discoverer, British chemist Sir Humphry Davy (1778–1829) because it was present in the mineral barytes "heavy spar," from Gk. barys "heavy" (see grave (adj.)).
Although soluble salts of barium are moderately toxic to humans, barium sulfate is nontoxic due to its insolubility. The most common means of inadvertent barium poisoning arises from the consumption of soluble barium salts mislabeled as BaSO4. In the Celobar incident (Brazil, 2003), nine patients died from improperly prepared radiocontrast agent.
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- Holleman, A. F. and Wiberg, E. (2001) Inorganic Chemistry, San Diego, CA : Academic Press, ISBN 0-12-352651-5
- Robert Kresse, Ulrich Baudis, Paul Jäger, H. Hermann Riechers, Heinz Wagner, Jochen Winkler, Hans Uwe Wolf, "Barium and Barium Compounds" in Ullmann's Encyclopedia of Industrial Chemistry, 2007 Wiley-VCH, Weinheim. doi:10.1002/14356007.a03_325.pub2
- Tieh-Chi Chu, Jeng-Jong Wang, “Radioactive Disequilibrium of Uranium and Thorium Nuclide Series in Hot Spring and River Water from Peitou Hot Spring Basin in Taipei”, Journal of Nuclear and Radiochemical Sciences, Vol. 1, No. 1, pp. 5−10, 2000. http://www.go2taiwan.net/monthly_selection.php?sqno=23