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Magnesium carbonate

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Magnesium carbonate
Magnesium carbonate.png
Magnesite-xtal-packing-a-3D-bs-17.png
Uhličitan hořečnatý.PNG
Names
Other names
Magnesite
Barringtonite (dihydrate)
Nesequehonite (trihydrate)
Lansfordite (pentahydrate)
Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.008.106
E number E504(i) (acidity regulators, ...)
PubChem CID
RTECS number
  • OM2470000
UNII
  • InChI=1S/CH2O3.Mg/c2-1(3)4;/h(H2,2,3,4);/q;+2/p-2 checkY
    Key: ZLNQQNXFFQJAID-UHFFFAOYSA-L checkY
  • InChI=1/CH2O3.Mg/c2-1(3)4;/h(H2,2,3,4);/q;+2/p-2
    Key: ZLNQQNXFFQJAID-NUQVWONBAU
  • [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)
10−7.8
Solubility Soluble in acid, aqueous CO2
Insoluble in acetone, ammonia
−32.4·10−6 cm3/mol
1.717 (anhydrous)
1.458 (dihydrate)
1.412 (trihydrate)
Structure
Trigonal
R3c, No. 167
Thermochemistry
75.6 J/mol·K
Std molar
entropy
(S298)
65.7 J/mol·K
−1113 kJ/mol
Gibbs free energy fG)
−1029.3 kJ/mol
Pharmacology
A02AA01 (WHO) A06AD01 (WHO)
Hazards
NFPA 704 (fire diamond)
1
0
0
Flash point Non-flammable
NIOSH (US health exposure limits):
PEL (Permissible)
  • TWA 15 mg/m3 (total)
  • TWA 5 mg/m3 (resp)
Safety data sheet (SDS) ICSC 0969
Related compounds
Other anions
Magnesium bicarbonate
Other cations
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 their standard state (at 25 °C [77 °F], 100 kPa).
☒N verify (what is checkY☒N ?)

Magnesium carbonate, MgCO3 (archaic name magnesia alba), is an inorganic salt that is a colourless or white solid. Several hydrated and basic forms of magnesium carbonate also exist as minerals.

Forms

The most common magnesium carbonate forms are the anhydrous salt called magnesite (MgCO3), and the di, tri, and pentahydrates known as barringtonite (MgCO3·2H2O), nesquehonite (MgCO3·3H2O), and lansfordite (MgCO3·5H2O), respectively. Some basic forms such as artinite (Mg2CO3(OH)2·3H2O), hydromagnesite (Mg5(CO3)4(OH)2·4H2O), and dypingite (Mg5(CO3)4(OH)2·5H2O) also occur as minerals. All of those minerals are colouress or white.

Magnesite consists of colourless or white trigonal crystals. The anhydrous salt is practically insoluble in water, acetone, and ammonia. All forms of magnesium carbonate react with acids. Magnesite crystallizes in the calcite structure wherein Mg2+ is surrounded by six oxygen atoms.

Crystal structure of magnesium carbonate
Carbonate coordination Magnesium coordination Unit cell
Carbonate-coordination-in-magnesite-3D-bs-17.png Magnesium-coordination-in-magnesite-3D-bs-17.png Magnesite-unit-cell-3D-bs-17.png

The dihydrate has a triclinic structure, while the trihydrate has a monoclinic structure.

References to "light" and "heavy" magnesium carbonates actually refer to the magnesium hydroxy carbonates hydromagnesite and dypingite, respectively.

Preparation

Magnesium carbonate is ordinarily obtained by mining the mineral magnesite. Seventy percent of the world's supply is mined and prepared in China.

Magnesium carbonate can be prepared in laboratory by reaction between any soluble magnesium salt and sodium 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 – a hydrated complex of magnesium carbonate and magnesium 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 through magnesium bicarbonate, which can be formed by combining a slurry of magnesium hydroxide and carbon dioxide at high pressure and moderate temperature. 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

With acids

Like many common group 2 metal carbonates, magnesium carbonate reacts with aqueous acids to release carbon dioxide and water:

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

Decomposition

At high temperatures MgCO3 decomposes to magnesium oxide and carbon dioxide. This process is important in the production of magnesium oxide. This process is called calcining:

MgCO3 → MgO + CO2 (ΔH = +118 kJ/mol)

The decomposition temperature is given as 350 °C (662 °F). 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. For example, in the trihydrate MgCO3·3H2O, which molecular formula may be written as Mg(HCO3)(OH)·2H2O, the dehydration steps occur at 157 °C and 179 °C as follows:

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

Uses

The primary use of magnesium carbonate is the production of magnesium oxide by calcining. Magnesite and dolomite minerals are used to produce refractory bricks.MgCO3 is also used in flooring, fireproofing, fire extinguishing compositions, cosmetics, dusting powder, and toothpaste. Other applications are as filler material, smoke suppressant in plastics, a reinforcing agent in neoprene rubber, a drying agent, and colour retention in foods.

Climber Jan Hojer blows surplus chalk from his hand. Boulder World Cup 2015

Because of its low solubility in water and hygroscopic properties, MgCO3 was first added to salt in 1911 to make it flow more freely. The Morton Salt company adopted the slogan "When it rains it pours", meaning that its salt containing MgCO3 would not stick together in humid weather. Magnesium carbonate, most often referred to as "chalk", is also used as a drying agent on athletes' hands in rock climbing, gymnastics, weightlifting and other sports in which a firm grip is necessary.

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

Magnesium carbonate is used in taxidermy for whitening skulls. It can be mixed with hydrogen peroxide to create a paste, which is spread on the skull to give it a white finish.

Magnesium carbonate is used as a matte white coating for projection screens.

Medical use

It is a laxative to loosen the bowels.

In addition, high purity magnesium carbonate is used as an antacid and as an additive in table salt to keep it free flowing. Magnesium carbonate can do this because it does not dissolve in water, only in acid, where it will effervesce (bubble).

Safety

Magnesium carbonate is non-toxic and non-flammable.

Compendial status

See also

External links


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