magnesium sulfate

Magnesium sulfate
IUPAC name	Magnesium sulfate
Other names	Epsom salt 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
RTECS number	OM4500000
ChemSpider ID	22515
Properties
Molecular formula	MgSO4
Molar mass	120.415 g/mol (anhydrous) 246.47 g/mol (heptahydrate)
Appearance	white crystalline solid
Density	2.66 g/cm3 (anhydrous) 2.445 g/cm3 (monohydrate) 1.68 g/cm3 (heptahydrate)
Melting point	1124 °C (anhydrous, decomp) 200 °C (monohydrate, decomp) 150 °C (heptahydrate, decomp)
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	0.0116 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
Related compounds
Other cations	Beryllium sulfate Calcium sulfate Strontium sulfate Barium sulfate
Y (what is this?)  (verify) 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 a chemical compound containing magnesium, sulfur and oxygen, with the formula MgSO₄. In its hydrated form the pH is 6.0 (5.5 to 6.5). It is often encountered as the heptahydrate, MgSO₄·7H₂O, commonly called Epsom salt. Anhydrous magnesium sulfate is used as a drying agent. Since 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.

Properties

Magnesium sulfate is the primary substance that causes the absorption of sound in seawater.^[1] Absorption, in this case, means the conversion of acoustic energy to heat energy. The conversion is a strong function of frequency. Lower frequencies are less affected by the salt, so that the acoustic energy travels much farther in the ocean. Boric acid also contributes to absorption, but much less than MgSO₄, and the most abundant salt in seawater, sodium chloride, has no effect on sound absorption.

Occurrence

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. Almost all known mineralogical forms of MgSO₄ occur as hydrates. Epsomite is the natural analogue of "Epsom salt," mentioned above. Another heptahydrate, the copper-containing mineral alpersite (Mg,Cu)SO₄·7H₂O^[2], was also 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.

Applications

In agriculture and gardening, magnesium sulfate is used to correct magnesium deficiency in soil, since magnesium is an essential element in the chlorophyll molecule. It is most commonly applied to potted plants, or to magnesium-hungry crops, such as potatoes, roses, tomatoes, peppers and cannabis. The advantage of magnesium sulfate over other magnesium soil amendments (such as dolomitic lime) is its high solubility.

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. This property is also used to restore some Lava lamps damaged by being shaken by exchanging the water and adding drops of a concentrated solution until sustainable buoyancy is reached. 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 ("pruning" -- 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. It is also sometimes found in bottled mineral water, and accordingly is sometimes listed in the contents thereof. It may also be used as a coagulant for making tofu.^[3]

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.^[4] It is also recommended for dropsy treatment for fish.^[5]

An old remedy for diarrhea in adult chickens is 1/2 tsp per bird per day added to their feed.^[6]

Medical use

Oral magnesium sulfate, or magnesium hydroxide, is commonly used as a saline laxative. Epsom salt is also available in a gel form for topical application in treating aches and pains.

Indications for its use are

• Replacement therapy for hypomagnesemia.^[7]
• 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.^[8]
• As a bronchodilator after beta-agonist and anticholinergic agents have been tried, e.g. in severe exacerbations of asthma.^[9] Recent studies have revealed that magnesium sulfate can be nebulized to reduce the symptoms of acute asthma.^[9] It is commonly administered via the intravenous route for the management of severe asthma attacks.
• Users of Epsom salt in the gel form have reported significant and lasting reduction of pain associated with fibromyalgia and osteoporosis.^{[citation needed]}
• A 2004 research study showed that both magnesium and sulfate are absorbed through the skin when bathing in 1% w/v solution.^[10]
• Magnesium sulfate can be used to treat eclampsia in pregnant women.^[11]
• Magnesium sulfate can also delay labor in the case of premature labor, to delay preterm birth.^[12]
• Intravenous magnesium sulfate may be able to prevent cerebral palsy in preterm babies.^[13]
• Solutions of sulfate salts such as Epsom salt may be given as first aid for barium chloride poisoning.^[14]
• Magnesium sulfate paste has been used as an agent for dehydrating (drawing) boils, carbuncles, and abscesses.^[15]
• Magnesium sulfate solution has also been shown to be an effective aid in the fight against blemishes and acne when applied directly to problematic areas, usually in poultice form.^[16] If combined with water and made into a cream, it can be applied to the face to remove blackheads.
• Magnesium sulfate, when used through soaking, can soothe muscle pains and help improve rough patches in the skin.^[17]
• The body's magnesium level increases when soaking with magnesium sulfate, which may increase feelings of relaxation and well-being.^[18]
• Soaking in a warm bath containing Epsom salt (magnesium sulfate) can be beneficial to soothe and relieve herpes outbreak symptoms, such as itching and lesions relating to genital herpes and shingles.^[19][20]

References