Magnesium hydroxide

Crystal structure
__ Mg 2+      __ OH -
General
Surname	Magnesium hydroxide
other names	Magnesium (II) hydroxide Brucite E  528 MAGNESIUM HYDROXIDE ( INCI )
Ratio formula	Mg (OH) 2
Brief description	colorless and odorless solid
External identifiers / databases
CAS number 1309-42-8 EC number 215-170-3 ECHA InfoCard 100,013,792 PubChem 73981 ChemSpider 14107 DrugBank DB09104 Wikidata Q407548
Drug information
ATC code	A02 AA04 G04 BX01
properties
Molar mass	58.33 g mol −1
Physical state	firmly
density	2.38 g cm −3
Melting point	350 ° C (decomposition)
solubility	very bad in water (9 mg l −1 at 18 ° C)
safety instructions
Please note the exemption from the labeling requirement for drugs, medical devices, cosmetics, food and animal feed GHS labeling of hazardous substances no GHS pictograms H and P phrases H: no H-phrases P: no P-phrases
Toxicological data	8500 mg kg −1 ( LD 50 ,  rat ,  oral )
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Magnesium hydroxide is a chemical compound of magnesium from the group of hydroxides . It is a colorless salt and a strong base . Due to its low solubility in water, an aqueous slurry only has a pH value of ~ 10, which is why magnesium hydroxide appears as an apparently weak base.

Occurrence

Brucite

In nature it occurs as a mineral brucite .

Extraction and presentation

Magnesium hydroxide is formed from magnesium oxide through hydration , analogous to the lime slaking of calcium oxide .

Magnesium hydroxide can be obtained from residual caustic potash extraction by precipitation with milk of lime (1) or from sea water by precipitation with burned dolomite (2). The product is then filtered and dried at about 100 ° C. Particularly pure magnesium hydroxide is created by the action of water on elemental magnesium (3).

(1) ${\displaystyle \mathrm {MgCl_{2}+Ca(OH)_{2}\longrightarrow Mg(OH)_{2}+CaCl_{2}} }$

(2) ${\displaystyle \mathrm {MgCl_{2}+CaO\cdot MgO+2\ H_{2}O\longrightarrow } }$

${\displaystyle \mathrm {2\ Mg(OH)_{2}+CaCl_{2}} }$

(3) ${\displaystyle \mathrm {Mg+2\ H_{2}O\longrightarrow Mg(OH)_{2}+H_{2}} }$

Blackboard chalk can contain magnesium oxide as well as calcium sulfate and calcium carbonate . Magnesium hydroxide is then formed when writing on blackboards with a damp cloth.

properties

Magnesium hydroxide is gradually converted to magnesium carbonate through the absorption of carbon dioxide in the air .

The crystal lattice of magnesium hydroxide (brucite) consists of a hexagonal close packing of hydroxide ions . Every second octahedron gap layer is occupied by magnesium ions (Mg ²⁺ ). This leads to a trigonal structure, space group P 3 m 1 (space group no.164 ) , lattice parameters a = 3.148 Å , c = 4.779 Å. Magnesium hydroxide is sparingly soluble in water and alkaline solutions , but readily soluble in acidic solutions (e.g. hydrochloric acid , nitric acid ). Magnesium hydroxide is also readily soluble in ammonium salt solutions, since the neutralization of ammonium and hydroxide to form ammonia and water results in only a low hydroxide concentration and thus the solubility product is not exceeded.

Magnesium hydroxide forms basic and neutral salts with acids .

At temperatures above 350 ° C, decomposition to magnesium oxide occurs slowly . At 600 ° C the equilibrium is practically on the side of the oxide .

${\displaystyle \mathrm {Mg(OH)_{2}\ {\xrightarrow {\Delta T}}\ MgO+H_{2}O} }$

use

Most of the magnesium hydroxide produced for industrial purposes is processed into magnesium oxide by calcining (burning) at 500–600 ° C.

Magnesium hydroxide is used as an edible oil additive (to bind sulfur dioxide ), as a flocculant for waste water treatment , as a flame retardant in thermoplastics (polyolefins, PVC) and elastomers, and as an additive in cleaning agents.

In medicine it is used as an antacid (medicine to neutralize stomach acid) and as a mild laxative .

Magnesium hydroxide is added to foods as an acidity regulator or release agent. It is approved in the EU as a food additive with the E number E 528.

Individual evidence

1. ↑ Entry on E 528: Magnesium hydroxide in the European database for food additives, accessed on June 27, 2020.
2. ↑ Entry on MAGNESIUM HYDROXIDE in the CosIng database of the EU Commission, accessed on March 7, 2020.
3. ↑ ^{a b c d e f g h} Entry on magnesium hydroxide in the GESTIS substance database of the IFA , accessed on December 22, 2019 (JavaScript required)
4. ↑ ^{a b c d} Arnold Willmes: Pocket book chemical substances . 3rd edition. Harri Deutsch Verlag, 2007, ISBN 9783817117871 , p. 682, ( limited preview in Google book search)
5. ↑ Dipl.-Ing. Bonar Marbun: Kinetics of the hydration of CaO and MgO , pp. 2 and 4ff, dissertation, February 2006, Faculty of Natural and Material Sciences, Clausthal University of Technology
6. ↑ L. Desgranges, G. Calvarin, G. Chevrier: Interlayer interactions in M ​​(OH) ₂ : a neutron diffraction study of Mg (OH) ₂ . In: Acta Crystallographica , B52, 1996, pp. 82-86, doi: 10.1107 / S0108768195008275 .
7. ↑ Erwin Riedel, Christoph Janiak: Inorganic Chemistry . 7th edition. Walter de Gruyter, 2007, ISBN 9783110189032 , p. 605, ( limited preview in the Google book search)
8. ^ ^{A b} A. F. Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 102nd edition. Walter de Gruyter, Berlin 2007, ISBN 978-3-11-017770-1 , pp. 1230-1231.
9. ↑ Entry on magnesium hydroxide. In: Römpp Online . Georg Thieme Verlag, accessed on June 13, 2014.
10. ↑ Additives in the EU ( Memento of the original from December 8, 2015 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. (As of January 2015; PDF; 147 kB) 
11. ↑ Homepage of the consumer initiative e. V. on food additives