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Milk of Magnesia

Magnesium hydroxide
Magnesium hydroxide
Magnesium hydroxide
Names
IUPAC name
Magnesium hydroxide
Other names
Milk of magnesia
Identifiers
1309-42-8 YesY
3D model (Jmol) Interactive image
ChEBI CHEBI:6637 YesY
ChEMBL ChEMBL1200718 N
ChemSpider 14107 YesY
ECHA InfoCard 100.013.792
EC Number 215-170-3
E number E528 (acidity regulators, ...)
485572
PubChem 14791
RTECS number OM3570000
UNII NBZ3QY004S YesY
Properties
Mg(OH)2
Molar mass 58.3197 g/mol
Appearance White solid
Odor odorless
Density 2.3446 g/cm3
Melting point 350 °C (662 °F; 623 K) decomposes
0.00064 g/100 mL (25 °C)
0.004 g/100 mL (100 °C)
5.61×10−12
−22.1·10−6 cm3/mol
1.559
Structure
Hexagonal, hP3
P3m1 No. 164
a = 0.312 nm, c = 0.473 nm
Thermochemistry
77.03 J/mol K
64 J·mol−1·K−1
−924.7 kJ·mol−1
-833.7 kJ/mol
Pharmacology
A02AA04 (WHO) G04BX01 (WHO)
Hazards
Safety data sheet External MSDS
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 1: Exposure would cause irritation but only minor residual injury. E.g., turpentine Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
Flash point Non-flammable
Lethal dose or concentration (LD, LC):
LD50 (median dose)
8500 mg/kg (rat, oral)
Related compounds
Other anions
Magnesium oxide
Other cations
Beryllium hydroxide
Calcium hydroxide
Strontium hydroxide
Barium hydroxide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N  (what is YesYN ?)
Infobox references

Magnesium hydroxide is the inorganic compound with the chemical formula Mg(OH)2. It occurs in nature as the mineral brucite. It is a white solid with low solubility in water (Ksp = 5.61×10−12, Magnesium hydroxide is a common component of antacids, such as milk of magnesia, as well as laxatives.

Combining a solution of many magnesium salts with basic water induces precipitation of solid Mg(OH)2:

On a commercial scale, Mg(OH)2 is produced by treating seawater with lime (Ca(OH)2). 600 m3 of seawater gives about one ton of Mg(OH)2. Ca(OH)2 is far more soluble than Mg(OH)2, the latter precipitates as a solid:

Most Mg(OH)2 that is produced industrially, as well as the small amount that is mined, is converted to fused magnesia (MgO). Magnesia is valuable because it is both a poor electrical conductor and an excellent thermal conductor.

When the patient drinks magnesium hydroxide, the suspension enters the stomach. Depending on how much was taken, one of two possible outcomes will occur.

As an antacid, magnesium hydroxide is dosed at approximately 0.5–1.5 g in adults and works by simple neutralization, where the hydroxide ions from the Mg(OH)2 combine with acidic H+ions produced in the form of hydrochloric acid by parietal cells in the stomach to produce water.

As a laxative, magnesium hydroxide is dosed at 2–5 g, and works in a number of ways. First, Mg2+ is poorly absorbed from the intestinal tract, so it draws water from the surrounding tissue by osmosis. Not only does this increase in water content soften the feces, it also increases the volume of feces in the intestine (intraluminal volume) which naturally stimulates intestinal motility. Furthermore, Mg2+ ions cause the release of cholecystokinin (CCK), which results in intraluminal accumulation of water, electrolytes, and increased intestinal motility. Although it has been stated in some sources, the hydroxide ions themselves do not play a significant role in the laxative effects of milk of magnesia, as basic solutions (i.e., solutions of hydroxide ions) are not strongly laxative, and non-basic Mg2+ solutions, like MgSO4, are equally strong laxatives mole for mole.


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