Magnesium sulfate

Magnesium sulfate
Anhydrous magnesium sulfate
Epsomite (heptahydrate)
IUPAC name Magnesium sulfate
Other names Epsom salt (heptahydrate) Bitter salts
Identifiers
CAS number	7487-88-9 Y, 14168-73-1 (monohydrate), 24378-31-2 (tetrahydrate), 15553-21-6 (pentahydrate), 13778-97-7 (hexahydrate), 10034-99-8 (heptahydrate)
PubChem	24083
ChemSpider	22515 Y
UNII	ML30MJ2U7I Y
DrugBank	DB00653
ChEBI	CHEBI:32599 Y
ChEMBL	CHEMBL1200456 N
RTECS number	OM4500000
ATC code	A06AD04,A12CC02 B05XA05 D11AX05 V04CC02
Jmol-3D images	Image 1
SMILES [Mg+2].[O-]S([O-])(=O)=O
InChI InChI=1S/Mg.H2O4S/c;1-5(2,3)4/h;(H2,1,2,3,4)/q+2;/p-2 Y Key: CSNNHWWHGAXBCP-UHFFFAOYSA-L Y InChI=1/Mg.H2O4S/c;1-5(2,3)4/h;(H2,1,2,3,4)/q+2;/p-2 Key: CSNNHWWHGAXBCP-NUQVWONBAQ
Properties
Molecular formula	MgSO4
Molar mass	120.366 g/mol (anhydrous) 246.47 g/mol (heptahydrate)
Appearance	white crystalline solid
Odor	odorless
Density	2.66 g/cm3 (anhydrous) 2.445 g/cm3 (monohydrate) 1.68 g/cm3 (heptahydrate) 1.512 g/cm3 (11-hydrate)
Melting point	anhydrous decomposes at 1124 °C monohydrate decomposes at 200 °C heptahydrate decomposes at 150 °C undecahydrate decomposes at 2 °C
Solubility in water	anhydrous 26.9 g/100 mL (0 °C) 25.5 g/100 mL (20 °C) heptahydrate 71 g/100 mL (20 °C)
Solubility	1.16 g/100 mL (18 °C, ether) slightly soluble in alcohol, glycerol insoluble in acetone
Refractive index (nD)	1.523 (monohydrate) 1.433 (heptahydrate)
Structure
Crystal structure	monoclinic (hydrate)
Hazards
MSDS	External MSDS
EU Index	Not listed
NFPA 704	0 1 0
Related compounds
Other cations	Beryllium sulfate Calcium sulfate Strontium sulfate Barium sulfate
N (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Magnesium sulfate (or magnesium sulphate) is an inorganic salt (chemical compound) containing magnesium, sulfur and oxygen, with the formula MgSO₄. It is often encountered as the heptahydrate sulfate mineral epsomite (MgSO₄·7H₂O), commonly called Epsom salt, named for a bitter saline spring from the town of Epsom in Surrey, England, where the salt was produced from the springs that arise where the porous chalk of the North Downs meets non-porous London clay. Epsom salt occurs naturally as a pure mineral. Another hydrate form is kieserite.

Anhydrous magnesium sulfate is used as a drying agent. The anhydrous form is hygroscopic (readily absorbs water from the air) and is therefore difficult to weigh accurately; the hydrate is often preferred when preparing solutions (for example, in medical preparations). Epsom salt has been traditionally used as a component of bath salts. Epsom salt can also be used as a beauty product. Athletes use it to soothe sore muscles, while gardeners use it to improve crops. It has a variety of other uses.^[1]

Properties [edit]

This section requires expansion. (May 2012)

Magnesium sulfate is highly soluble in water. The anhydrous form is strongly hygroscopic, and can be used as a desiccant.

Epsom salts have medicinal properties when used both externally and internally.

Magnesium sulfate is the primary substance that causes the absorption of sound in seawater^[2] (acoustic energy is converted to thermal energy). Absorption is strongly dependent on frequency: lower frequencies are less absorbed by the salt, so that the sound travels much farther in the ocean. Boric acid also contributes to absorption, but the most abundant salt in seawater, sodium chloride, has negligible sound absorption.

Hydrates [edit]

Almost all known mineralogical forms of MgSO₄ occur as hydrates. Epsomite is the natural analogue of "Epsom salt". Another heptahydrate, the copper-containing mineral alpersite (Mg,Cu)SO₄·7H₂O,^[3] was recently recognized. Both are, however, not the highest known hydrates of MgSO₄, due to the recent terrestrial find of meridianiite, MgSO₄·11H₂O, which is thought to also occur on Mars. Hexahydrite is the next lower (6) hydrate. Three next lower hydrates — pentahydrite (5), starkeyite (4) and especially sanderite (2) — are more rarely found. Kieserite is a monohydrate and is common among evaporitic deposits. Anhydrous magnesium sulfate was reported from some burning coal dumps but never treated as a mineral.

The pH of hydrates is average 6.0 (5.5 to 6.5). Magnesium hydrates have, like copper(II) sulfate, coordinated water.^[4]

Manufacturing [edit]

The heptahydrate can be prepared by neutralizing sulfuric acid with magnesium carbonate or oxide, but it is usually obtained directly from natural sources.

Anhydrous magnesium sulfate is prepared only by the dehydration of a hydrate.

Occurrence [edit]

Magnesium sulfates are common minerals in geological environments. Their occurrence is mostly connected with supergene processes. Some of them are also important constituents of evaporitic potassium-magnesium (K-Mg) salts deposits.

Applications [edit]

Anhydrous magnesium sulfate is commonly used as a desiccant in organic synthesis due to its affinity for water. During work-up, an organic phase is saturated with magnesium sulfate until it no longer forms clumps. The hydrated solid is then removed with filtration or decantation. Other inorganic sulfate salts such as sodium sulfate and calcium sulfate may also be used in the same way.

Magnesium sulfate is used in bath salts, particularly in flotation therapy where high concentrations raise the bath water's specific gravity, effectively making the body more buoyant. Traditionally, it is also used to prepare foot baths, intended to soothe sore feet. The reason for the inclusion of the salt is partially cosmetic: the increase in ionic strength prevents some of the temporary skin wrinkling (partial maceration) which is caused by prolonged immersion of extremities in pure water. However, magnesium sulfate can also be absorbed into the skin, reducing inflammation.^[5] It is naturally present in some mineral waters.^{[citation needed]}

It may also be used as a coagulant for making tofu.^[6]

Magnesium sulfate heptahydrate is also used to maintain the magnesium concentration in marine aquaria which contain large amounts of stony corals as it is slowly depleted in their calcification process. In a magnesium-deficient marine aquarium calcium and alkalinity concentrations are very difficult to control because not enough magnesium is present to stabilize these ions in the saltwater and prevent their spontaneous precipitation into calcium carbonate.^[7]

Magnesium sulfate is used as the electrolyte to prepare copper sulfate. A magnesium sulfate solution is electrolyzed with a copper anode to form copper sulfate, magnesium hydroxide, and hydrogen:

Cu + MgSO₄ + 2 H₂O → H₂ + CuSO₄ + Mg(OH)₂.^{[citation needed]}

Magnesium sulfate is used as a brewing salt in beer production to adjust the ion content of the brewing water and enhance enzyme action in the mash or promote a desired flavor profile in the beer.

Agriculture [edit]

In gardening and other agriculture, magnesium sulfate is used to correct a magnesium or sulfur deficiency in soil; magnesium is an essential element in the chlorophyll molecule, and sulfur is another important micronutrient. It is most commonly applied to potted plants, or to magnesium-hungry crops, such as potatoes, roses, tomatoes, lemon trees, peppers and cannabis. The advantage of magnesium sulfate over other magnesium soil amendments (such as dolomitic lime) is its high solubility, which also allows the option of foliar feeding. Solutions of magnesium sulfate are also nearly neutral, as compared to alkaline salts of magnesium, as found in limestone; therefore the use of magnesium sulfate as a magnesium source for soil does not significantly change the soil pH.^{[citation needed]}

Medical use [edit]

Magnesium sulfate is a common pharmaceutical preparation of magnesium, commonly known as Epsom salts, used both externally and internally. Epsom salts are used as bath salts. The sulfate is supplied in a gel preparation for topical application in treating aches and pains.^{[citation needed]} Oral magnesium sulfate is commonly used as a saline laxative or osmotic purgative. Magnesium sulfate is the main preparation of intravenous magnesium.

Indications for internal use are:

• Replacement therapy for hypomagnesemia.^[8]
• Magnesium sulfate is the first-line antiarrhythmic agent for torsades de pointes in cardiac arrest under the 2005 ECC guidelines and for managing quinidine-induced arrhythmias.^[9]
• As a bronchodilator after beta-agonist and anticholinergic agents have been tried, e.g. in severe exacerbations of asthma.^[10] Studies conducted have revealed that magnesium sulfate can be nebulized to reduce the symptoms of acute asthma.^[10] It is commonly administered via the intravenous route for the management of severe asthma attacks.
• Magnesium sulfate can be used to treat eclampsia in pregnant women.^[11]
• Magnesium sulfate can also delay labor (tocolysis) by inhibiting uterine muscle contraction in the case of premature labor, to delay preterm birth.^[12][13] However, meta-analyses have failed to support it as a tocolytic agent.^[14][15]
• Intravenous magnesium sulfate has been shown to prevent cerebral palsy in preterm babies.^[16] A recent systematic review suggests that antenatal intravenous magnesium sulphate can reduce the risk of cerebral palsy and gross motor dysfunction in preterm infants by on average 30%.^[17]
• Magnesium sulfate has been used as an experimental treatment of Irukandji syndrome caused by envenomation by certain species of Irukandji jellyfish, however the efficacy of this treatment remains unproven.^[18]
• Solutions of sulfate salts such as Epsom salt may be given as first aid for barium chloride poisoning.^[19]

An overdose of magnesium causes hypermagnesemia.

References [edit]

External links [edit]

• International Chemical Safety Cards - Magnesium Sulfate