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chemical compound containing the sulfate (SO4) radicalradical,
in chemistry, group of atoms that are joined together in some particular spatial structure and that take part in most chemical reactions as a single unit. Important inorganic radicals include ammonium, NH4; carbonate, CO3 ; chlorate, ClO3
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. Sulfates are salts or esters of sulfuric acidsulfuric acid,
chemical compound, H2SO4, colorless, odorless, extremely corrosive, oily liquid. It is sometimes called oil of vitriol. Concentrated Sulfuric Acid

When heated, the pure 100% acid loses sulfur trioxide gas, SO3
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, H2SO4, formed by replacing one or both of the hydrogens with a metal (e.g., sodium) or a radical (e.g., ammonium or ethyl). Sulfates in which both hydrogens are replaced are called normal sulfates; sulfates in which only one hydrogen is replaced are called hydrogen sulfates, acid sulfates, or bisulfates. Most metal sulfates are readily soluble in water, but calcium and mercuric sulfates are only slightly soluble, while barium, lead, strontium, and mercurous sulfates are insoluble. In chemical analysis, the sulfate ionion,
atom or group of atoms having a net electric charge. Positive and Negative Electric Charges

A neutral atom or group of atoms becomes an ion by gaining or losing one or more electrons or protons.
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, SO4−2, is usually detected by adding barium chloride solution; the white barium sulfate precipitate that forms is insoluble in hydrochloric acid. Sulfates are widely distributed in nature. Barium sulfate occurs as baritebarite
, barytes
[New Lat., from barium], or heavy spar,
a white, yellow, blue, red, or colorless mineral. It is a sulfate of barium, BaSO4, found in nature as tabular crystals or in granular or massive form and has a high specific gravity.
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; calcium sulfate is found as gypsumgypsum
, mineral composed of calcium sulfate (calcium, sulfur, and oxygen) with two molecules of water, CaSO4·2H2O. It is the most common sulfate mineral, occurring in many places in a variety of forms. A transparent crystalline variety is selenite.
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, alabasteralabaster,
fine-grained, massive, translucent variety of gypsum, a hydrous calcium sulfate. It is pure white or streaked with reddish brown. Alabaster, like all other forms of gypsum, forms by the evaporation of bedded deposits that are precipitated mainly from evaporating
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, and selenite; Epsom saltsEpsom salts,
common name for magnesium sulfate heptahydrate, MgSO4·7H2O, a water-soluble bitter-tasting compound that occurs as white or colorless needle-shaped crystals.
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 is magnesium sulfate; sodium sulfatesodium sulfate,
chemical compound, Na2SO4. It is a white, orthorhombic crystalline compound at ordinary temperatures; above 100°C; it assumes a monoclinic structure, and above about 250°C; it assumes a hexagonal structure.
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 occurs as its decahydrate, Glauber's saltGlauber's salt,
common name for sodium sulfate decahydrate, Na2SO4·10H2O; it occurs as white or colorless monoclinic crystals. Upon exposure to fairly dry air it effloresces, forming powdery anhydrous sodium sulfate.
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; and strontium sulfate occurs as celestitecelestite
or celestine
, mineral appearing in blue-tinged or white orthorhombic crystals or in fibrous masses. The natural sulfate of strontium, SrSO4, it is important as a source of strontium and of certain of its compounds, e.g.
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. Some sulfates were formerly known as vitriols; blue vitriol is cupric sulfatecupric sulfate
or copper (II) sulfate,
chemical compound, CuSO4, taking the form of white rhombohedral crystals or amorphous powder. It decomposes at 650°C; to cupric oxide (CuO).
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, green vitriol is ferrous sulfateferrous sulfate
or iron (II) sulfate,
chemical compound, FeSO4. It is known as the monohydrate, FeSO4·H2O; the tetrahydrate, FeSO4·4H2O; the pentahydrate, FeSO4·5H2
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, and white vitriol is zinc sulfatezinc sulfate,
chemical compound ZnSO4, a very water soluble, transparent, colorless, crystalline compound. It is commonly used as the heptahydrate, ZnSO4·7H2
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. Alumsalum
, any one of a series of isomorphous double salts that are hydrated sulfates of a univalent cation (e.g., potassium, sodium, ammonium, cesium, or thallium) and a trivalent cation (e.g., aluminum, chromium, iron, manganese, cobalt, or titanium).
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 are double sulfates, containing two different metals and two sulfate radicals. Organic sulfates are esters. They can be formed by reacting an alcohol with cold sulfuric acid. They are also formed by the reaction of sulfuric acid with a double bond in an alkene; the product is called an alkyl hydrogen sulfate. An alkyl hydrogen sulfate can be broken down to an alcohol and sulfuric acid by heating it with water (hydrolysishydrolysis
, chemical reaction of a compound with water, usually resulting in the formation of one or more new compounds. The most common hydrolysis occurs when a salt of a weak acid or weak base (or both) is dissolved in water.
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); this reaction is often used to synthesize alcohols. Sulfates play a significant role both in the chemical industry and in biological systems. Sulfuric acid is used in lead storage batteries and in the manufacture of nitric acid; copper sulfate is a common algicide. Organisms found near deep-sea thermal vents use sulfates for energy in place of sunlight.
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The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



any one of various salts of sulfuric acid, H2SO4. There are two series of sulfates: the normal sulfates, M2SO4, and the acid sulfates, MHSO4, where M is a monovalent metal.

Sulfates are crystalline compounds, which are colorless if the cation is colorless, and in most cases are readily soluble in water. Sparingly soluble sulfates are encountered as the minerals gypsum, CaSO4·2H2O; celestite, SrSO4; and anglesite, PbSO4. The mineral barite, BaSO4, and RaSO4 are virtually insoluble in water. Acid sulfates have been isolated in the solid state only for the most reactive metals, such as sodium and potassium. These salts are readily soluble in water, and they fuse easily. Normal sulfates may be obtained by dissolving metals in sulfuric acid and by the action of sulfuric acid on oxides, hydroxides, and carbonates of metals. Acid sulfates are obtained by heating normal sulfates with concentrated H2SO4:

K2SO4 + H2SO4 = 2KHSO4

The crystal hydrates of the sulfate salts of some heavy metals are called vitriols.

Sulfate minerals are widely used in many branches of industry.


The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.


A compound containing the ‒SO4 group, as in sodium sulfate, Na2SO4.
A salt of sulfuric acid.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.