Wikipedia

Magnesium carbonate

Magnesium carbonate,MgCO3(archaic namemagnesia alba), is an inorganic salt that is a colourless or white solid. Severalhydratedandbasicforms of magnesium carbonate also exist asminerals.

Magnesium carbonate
Names
Other names
Magnesite
Barringtonite (dihydrate)
Nesequehonite (trihydrate)
Lansfordite(pentahydrate)
Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.008.106Edit this at Wikidata
E number E504(i)(acidity regulators,...)
RTECS number
  • OM2470000
UNII
  • InChI=1S/CH2O3.Mg/c2-1(3)4;/h(H2,2,3,4);/q;+2/p-2checkY
    Key: ZLNQQNXFFQJAID-UHFFFAOYSA-LcheckY
  • InChI=1/CH2O3.Mg/c2-1(3)4;/h(H2,2,3,4);/q;+2/p-2
    Key: ZLNQQNXFFQJAID-NUQVWO NBA U
  • [Mg+2].[O-]C([O-])=O
Properties
MgCO3
Molar mass 84.3139 g/mol (anhydrous)
Appearance Colourless crystals or white solid
Hygroscopic
Odor Odorless
Density 2.958 g/cm3(anhydrous)
2.825 g/cm3(dihydrate)
1.837 g/cm3(trihydrate)
1.73 g/cm3(pentahydrate)
Melting point 350 °C (662 °F; 623 K)
decomposes (anhydrous)
165 °C (329 °F; 438 K)
(trihydrate)
Anhydrous:
0.0139 g/100 ml (25 °C)
0.0063 g/100 ml (100 °C)[1]
10−7.8[2]
Solubility Soluble in acid, aqueousCO2
Insoluble inacetone,ammonia
−32.4·10−6cm3/mol
1.717 (anhydrous)
1.458 (dihydrate)
1.412 (trihydrate)
Structure
Trigonal
R3c, No. 167[3]
Thermochemistry
75.6 J/mol·K[1]
65.7 J/mol·K[1][4]
−1113 kJ/mol[4]
−1029.3 kJ/mol[1]
Pharmacology
A02AA01(WHO)A06AD01(WHO)
Hazards
NFPA 704(fire diamond)
NFPA 704 four-colored diamondHealth 1: Exposure would cause irritation but only minor residual injury. E.g. turpentineFlammability 0: Will not burn. E.g. waterInstability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
1
0
0
Flash point Non-flammable
NIOSH(US health exposure limits):
PEL(Permissible)
  • TWA 15 mg/m3(total)
  • TWA 5 mg/m3(resp)[5]
Safety data sheet(SDS) ICSC 0969
Related compounds
Otheranions
 Magnesium bicarbonate
Othercations
 Beryllium carbonate
Calcium carbonate
Strontium carbonate
Barium carbonate
Radium carbonate
Related compounds
 Artinite
Hydromagnesite
Dypingite
Except where otherwise noted, data are given for materials in theirstandard state(at 25 °C [77 °F], 100 kPa).

Forms

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The most common magnesium carbonate forms are theanhydroussalt calledmagnesite(MgCO3), and the di, tri, and pentahydrates known as barringtonite (MgCO3·2H2O), nesquehonite (MgCO3·3H2O), and lansfordite (MgCO3·5H2O), respectively.[6]Some basic forms such asartinite(Mg2CO3(OH)2·3H2O),hydromagnesite(Mg5(CO3)4(OH)2·4H2O), anddypingite(Mg5(CO3)4(OH)2·5H2O) also occur asminerals.All of those minerals are colourless or white.

Magnesite consists of colourless or whitetrigonalcrystals.The anhydrous salt is practicallyinsolubleinwater,acetone,andammonia.All forms of magnesium carbonate react withacids.Magnesite crystallizes in thecalcitestructure whereinMg2+issurrounded bysixoxygenatoms.[3]

Crystal structure of magnesium carbonate
Carbonate coordination Magnesium coordination Unit cell

The dihydrate has atriclinicstructure, while the trihydrate has amonoclinicstructure.

References to "light" and "heavy" magnesium carbonates actually refer to the magnesium hydroxy carbonateshydromagnesiteanddypingite,respectively.[7]The "light" form is precipitated from magnesium solutions using alkali carbonate at "normal temperatures" while the "heavy" may be produced from boiling concentrated solutions followed by precipitation to dryness, washing of the precipitate, and drying at 100 C.[8]

Preparation

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Magnesium carbonate is ordinarily obtained by mining the mineralmagnesite.Seventy percent of the world's supply is mined and prepared in China.[9]

Magnesium carbonate can be prepared in laboratory by reaction between any soluble magnesium salt andsodium bicarbonate:

MgCl2(aq) + 2 NaHCO3(aq) →MgCO3(s) + 2 NaCl(aq) + H2O(l) + CO2(g)

If magnesium chloride (or sulfate) is treated with aqueous sodium carbonate, a precipitate of basic magnesium carbonate – ahydratedcomplex of magnesium carbonate andmagnesium hydroxide– rather than magnesium carbonate itself is formed:

5 MgCl2(aq) + 5 Na2CO3(aq) + 5 H2O(l) →Mg4(CO3)3(OH)2·3H2O(s) + Mg(HCO3)2(aq) + 10 NaCl(aq)

High purity industrial routes include a path throughmagnesium bicarbonate,which can be formed by combining aslurryof magnesium hydroxide andcarbon dioxideat high pressure and moderate temperature.[6]The bicarbonate is then vacuum dried, causing it to lose carbon dioxide and a molecule of water:

Mg(OH)2+ 2 CO2→ Mg(HCO3)2
Mg(HCO3)2→ MgCO3+ CO2+ H2O

Chemical properties

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With acids

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Like many common group 2 metal carbonates, magnesium carbonate reacts with aqueous acids to releasecarbon dioxideandwater:

MgCO3+ 2 HCl → MgCl2+ CO2+ H2O
MgCO3+ H2SO4→ MgSO4+ CO2+ H2O

Decomposition

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At high temperatures MgCO3decomposes tomagnesium oxideandcarbon dioxide.This process is important in the production of magnesium oxide.[6]This process is calledcalcining:

MgCO3→ MgO + CO2(ΔH = +118 kJ/mol)

The decomposition temperature is given as 350 °C (662 °F).[10][11] However, calcination to the oxide is generally not considered complete below 900 °C due to interfering readsorption of liberated carbon dioxide.

The hydrates of the salts lose water at different temperatures during decomposition.[12]For example, in the trihydrateMgCO3·3H2O,which molecular formula may be written asMg(HCO3)(OH)·2H2O,the dehydration steps occur at 157 °C and 179 °C as follows:[12]

Mg(HCO3)(OH)·2(H2O) → Mg(HCO3)(OH)·(H2O) + H2Oat 157 °C
Mg(HCO3)(OH)·(H2O) → Mg(HCO3)(OH) + H2Oat 179 °C

Uses

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The primary use of magnesium carbonate is the production ofmagnesium oxidebycalcining.Magnesite anddolomiteminerals are used to producerefractory bricks.[6]MgCO3is also used inflooring,fireproofing,fire extinguishing compositions,cosmetics,dusting powder,andtoothpaste.Other applications are asfiller material,smoke suppressant in plastics, a reinforcing agent inneoprenerubber, adrying agent,and colour retention in foods.

Because of its low solubility in water andhygroscopicproperties,MgCO3was first added totable salt(NaCl) in 1911 to make it flow more freely. TheMorton Saltcompany adopted the slogan "When it rains it pours", highlighting that its salt, which containedMgCO3,would not stick together in humid weather.[13]

ClimberJan Hojerblows surpluschalkfrom his hand. Boulder World Cup 2015

Powdered magnesium carbonate, known asclimbing chalkorgym chalkis also used as a drying agent on athletes' hands inrock climbing,gymnastics,powerlifting,weightliftingand other sports in which a firm grip is necessary.[9]A variant isliquid chalk.

As afood additive,magnesium carbonate is known as E504. Its only known side effect is that it may work as a laxative in high concentrations.[14]

Magnesium carbonate is used intaxidermyfor whitening skulls. It can be mixed withhydrogen peroxideto create a paste, which is spread on the skull to give it a white finish.

Magnesium carbonate is used as a matte white coating forprojection screens.[15]

Medical use

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It is alaxativeto loosen thebowels.

In addition, high purity magnesium carbonate is used as anantacidand as an additive intable saltto keep it free flowing. Magnesium carbonate can do this because it does not dissolve in water, only in acid, where it willeffervesce(bubble).[16]

Safety

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Magnesium carbonate is non-toxic and non-flammable.

Compendial status

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See also

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Notes and references

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  1. ^abcd"Magnesium carbonate".
  2. ^Bénézeth, Pascale; Saldi, Giuseppe D.; Dandurand, Jean-Louis; Schott, Jacques (2011). "Experimental determination of the solubility product of magnesite at 50 to 200 °C".Chemical Geology.286(1–2): 21–31.Bibcode:2011ChGeo.286...21B.doi:10.1016/j.chemgeo.2011.04.016.
  3. ^abRoss, Nancy L. (1997). "The equation of state and high-pressure behavior of magnesite".Am. Mineral.82(7–8): 682–688.Bibcode:1997AmMin..82..682R.doi:10.2138/am-1997-7-805.S2CID43668770.
  4. ^abZumdahl, Steven S. (2009).Chemical Principles 6th Ed.Houghton Mifflin Company. p. A22.ISBN978-0-618-94690-7.
  5. ^NIOSH Pocket Guide to Chemical Hazards."#0373".National Institute for Occupational Safety and Health(NIOSH).
  6. ^abcdMargarete Seeger; Walter Otto; Wilhelm Flick; Friedrich Bickelhaupt; Otto S. Akkerman. "Magnesium Compounds".Ullmann's Encyclopedia of Industrial Chemistry.Weinheim: Wiley-VCH.doi:10.1002/14356007.a15_595.pub2.ISBN978-3527306732.
  7. ^Botha, A.; Strydom, C.A. (2001). "Preparation of a magnesium hydroxy carbonate from magnesium hydroxide".Hydrometallurgy.62(3): 175.Bibcode:2001HydMe..62..175B.doi:10.1016/S0304-386X(01)00197-9.
  8. ^J.R. Partington (1951).General and inorganic chemistry, 2nd ed.
  9. ^abAllf, Bradley (21 May 2018)."The Hidden Environmental Cost of Climbing Chalk".Climbing Magazine.Cruz Bay Publishing.Retrieved22 May2018.In fact, China produces 70 percent of the world's magnesite. Most of that production—both mining and processing—is concentrated in a small corner of Liaoning, a hilly industrial province in northeast China between Beijing and North Korea.
  10. ^"IAState MSDS".
  11. ^Weast, Robert C.; et al. (1978).CRC Handbook of Chemistry and Physics(59th ed.). West Palm Beach, FL: CRC Press. p. B-133.ISBN0-8493-0549-8.
  12. ^ab"Conventional and Controlled Rate Thermal analysis of nesquehonite Mg(HCO3)(OH)·2(H2O) "(PDF).
  13. ^"Her Debut - Morton Salt".Retrieved27 December2017.
  14. ^"Food-Info.net: E-numbers: E504: Magnesium carbonates".080419 food-info.net
  15. ^Noronha, Shonan (2015).Certified Technology Specialist-Installation.McGraw Hill Education. p. 256.ISBN978-0071835657.
  16. ^"What Is Magnesium Carbonate?".Sciencing.Retrieved15 April2018.
  17. ^British Pharmacopoeia Commission Secretariat (2009)."Index, BP 2009"(PDF).Archived fromthe original(PDF)on 11 April 2009.Retrieved31 January2010.
  18. ^"Japanese Pharmacopoeia, Fifteenth Edition"(PDF).2006. Archived fromthe original(PDF)on 22 July 2011.Retrieved31 January2010.
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