Магния гидроксид

Описание

A white, bulky powder. It dissolves in dilute acids, but is practically insoluble in water and in alcohol.

Химические свойства

Magnesium hydroxide, Mg(OHn, also known as magnesium hydrate and brucite, is a white powder that is very slightly soluble in water. It decomposes at 350°C (662 OF). It is used in the extraction of magnesium metal and as a reagent in the sulfite wood pulp process. Magnesium hydroxide is formed by the reaction of sodium hydroxide and a soluble magnesium salt solution. Brucite, a mineral composed of magnesium hydroxide with occasional traces of iron and manganese, is a white to grayish translucent secondary mineral found with serpentine and metamorphic dolomites.

Физические свойства

Magnesium Hydroxide decomposes when heated to 360°C and forms the oxide, MgO. It is very slightly soluble in water at 0.00122 g/100 ml and has a solubility product of 5.61×10^-12. Crystals of Mg(OH)2 have a refractive index of 1.559. Its heat of formation is –925 kJ/mol with an entropy of 63 J/mol·K.
As a suspension in water, it is often called milk of magnesia because of its milk-like appearance. The solid mineral form of magnesium hydroxide is known as “brucite”.
It can be prepared by the metathesis reaction between any soluble magnesium salts and an alkali hydroxide such as sodium or even ammonium:
Mg²⁺(aq)＋2OH^-(aq)→Mg(OH)2(solid)
Magnesium hydroxide is a common component of antacids and laxatives. It interferes with the absorption of folic acid and iron. Its low solubility makes it a weak base. Another method of commercial manufacture of magnesium hydroxide involves the chloride obtained from seawater. After the chloride is recrystallized several times to obtain a level of purity, it is calcined at about 1000°C:
MgCl2·6H2O → MgCl2＋6H2O
→ Mg(OH)_-xCl2_-x＋xHCl
→ MgO＋(2－x)HCl

Вхождение

Magnesium Hydroxide occurs naturally as the mineral brucite. Brucite, usually found as a low temperature, hydrothermal vein mineral associated with calcite, aragonite, talc, or magnesite, appears as a decomposition product of magnesium silicates associated with serpentine, dolomite, magnesite, and chromite. Brucite also occurs as a hydrated form of periclase, and is found in serpentine, marble, chlorite schists, and in crystalline limestone.

Использование

Magnesium Hydroxide is an alkali that is a general purpose food additive. it exists as a white powder and has poor solubility in water and in alcohol. in frozen desserts it will increase the tendency for fat globules to clump, which results in an increase in dryness. it reacts with triglycerides in fatty acids to form soaps. it also functions as a drying agent in foods.

Определение

ChEBI: A magnesium hydroxide in which the magnesium atom is bound to two hydroxide groups.

Фармацевтические приложения

The synthesis of magnesium hydroxide [Mg(OH)₂] is based on a metathesis reaction in which magnesium salts are reacted with sodium or potassium hydroxide.
Magnesium hydroxide (Mg(OH)₂) has only limited solubility in water and the resulting suspension is called milk of magnesia, which is commonly used as an antacid and is known to be a mild base.
Magnesium hydroxide [Mg(OH)₂] is present in antacids because of its laxative properties and is also the main ingredient of the ‘milk of magnesia’. The ‘milk of magnesia’ is a suspension of Mg(OH)₂ in water, which has a milk-like appearance because of the low aqueous solubility of Mg(OH)₂. It is considered as a strong electrolyte and a weak base and is given to the patient for indigestion and heartburn. The alkaline suspension neutralises any excess stomach acid and therefore works as an antacid. It also stimulates intestinal movement, as the magnesium ions increases the water content in the intestines through its osmotic effect and as a result softens any faeces present.

Профиль безопасности

Moderately toxic by intraperitoneal route. Human systemic effects: chlorine level changes, coma, somnolence. Incompatible with maleic anhydride, phosphorus. See also MAGNESIUM COMPOUNDS.