Barium sulfate
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| Identifiers | |||
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| ECHA InfoCard | 100.028.896 | ||
| RTECS number |
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CompTox Dashboard (EPA)
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| Properties | |||
| BaSO4 | |||
| Molar mass | 233.43 g/mol | ||
| Appearance | white crystalline | ||
| Density | 4.50 g/cm3 | ||
| Melting point | 1580 °C | ||
| Boiling point | 1600 °C (decomp) | ||
| 0.0002448 g/100 mL (20°C) 0.000285 g/100 mL (30 °C) | |||
Solubility product (Ksp)
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1.0842 × 10-10 (25°C) | ||
| Solubility | soluble in alcohol, concentrated sulfuric acid | ||
Refractive index (nD)
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1.64 | ||
| Pharmacology | |||
| Pharmacokinetics: | |||
| negligible orally | |||
| Hazards | |||
| NFPA 704 (fire diamond) | |||
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Barium sulfate is a white crystalline solid with the chemical formula BaSO4. It is insoluble in water and other traditional solvents but is soluble in concentrated sulfuric acid. The mineral barite is composed largely of barium sulfate and is a common ore of barium. It is often extracted in a blast furnace, as it can cope with high temperature.
Uses
Catalyst support
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. Alkenes are liable to be hydrogenated further into alkanes, which reaction the special support and poison prevent.
Radiocontrast agent
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 extremely 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.
Pigment
Barium sulfate mixtures are used as 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 and barium sulfate. Barium sulfate itself is called blanc fixe (French for "permanent white"). The combination of barium sulfate and zinc sulfide (ZnS) is called lithopone.
Pyrotechnics
Barium sulfate is also used as a high temperature oxidizer in certain pyrotechnic formulas, as barium compounds emit a green light when burned. Barium nitrate is more common in green pyrotechnic formulas, as it contains an oxidizer while still producing green colored light.
Other uses
Barium sulfate is used as a filler in plastics and as a component of oil well drilling fluid to increase the density. It is also used in Episal salt, brake linings, anacoustic foams, powder coatings, and root canal filling.
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) which would otherwise 'cloud' solution preventing one from seeing the colour of the pH indicator i.e. the result of the test.
In colorimetry barium sulfate is used as a near-perfect diffuser when measuring light sources.
In photography it is used as a coating for certain photographic papers.
In metal casting, the moulds used are often coated with barium sulfate in order to prevent the molten metal from bonding with the mould.
History
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.]
Etymology
Barium, 1808, Mod.L., from Gk. barys "heavy;" so called by its discoverer, British chemist Sir Humphrey Davy (1778-1829) because it was present in the mineral barytes "heavy spar," from Gk. barys "heavy" (see grave (adj.)).
Reactions
Barium sulfate is one of the most insoluble salts of barium. It does not undergo double decomposition reactions in aqueous phase. It dissolves in concentrated sulfuric acid to form an acid sulfate which breaks down to barium sulfate upon dilution. Reduction with coke under heating produces barium sulfide:
- BaSO4 + 4C + heat → BaS + 4CO
It reacts violently when heated with aluminum or explosively when mixed with potassium. [1]
See also
- The Celobar incident (Brazil, 2003), when nine patients died from improperly made BaSO4 radiocontrast.
References
- ^ Pradyot Patnaik. Handbook of Inorganic Chemicals. McGraw-Hill, 2002, ISBN 0070494398
- Holleman, A. F. and Wiberg, E. (2001) Inorganic Chemistry, San Diego, CA : Academic Press, ISBN 0-12-352651-5