Magnesium chloride

Magnesium chloride

A sample of hygroscopic food-grade MgCl2·6H2O
Names
IUPAC name Magnesium chloride
Systematic IUPAC name Magnesium chloride
Other names E511 Nigari Nigari salt
Identifiers
Jmol-3D images	Image
SMILES [Mg+2].[Cl-].[Cl-]
Properties
Chemical formula	MgCl2 (anhydrous) MgCl2·6H2O (hexahydrate)
Molar mass	95.211 g/mol (anhydrous) 203.31 g/mol (hexahydrate)
Appearance	White or colorless crystalline hygroscopic solid
Density	2.32 g/cm3 (anhydrous) 1.569 g/cm3 (hexahydrate)
Melting point	714 °C (1,317 °F; 987 K) 117 °C (243 °F; 390 K) (hexahydrate)
Solubility in water	anhydrous 52.9 g/100 mL (0 °C) 54.3 g/100 mL (20 °C) 72.6 g/100 mL (100 °C) hexahydrate 167 g/100 mL (20 °C)
Solubility	Soluble in conc. HCl, methanol Slightly soluble in acetone, ethanol, pyridine
Solubility in ethanol	3.61 g/100 mL (0 °C) 7.4 g/100 mL (30 °C) 15.89 g/100 mL (60 °C)
Solubility in methanol	15.5 g/100 mL (0 °C) 20.4 g/100 mL (60 °C)
Vapor pressure	~0 mmHg
Thermochemistry
Std molar entropy (So298)	89.88 J·mol-1·K-1
Std enthalpy of formation (ΔfHo298)	-641.1 kJ/mol
Hazards
Safety data sheet	ICSC 0764
Flash point	Non-flammable
Lethal dose or concentration (LD, LC):
LD50 (Median dose)	2,800 mg/kg (oral, rat)
Related compounds
Related compounds	Calcium chloride Strontium chloride Barium chloride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Magnesium chloride, also known as Nigari, is a chemical compounds with the formula MgCl₂.

Properties

Chemical

Magnesium chloride will react with calcium hydroxide to give magnesium hydroxide and calcium chloride:

MgCl_2(aq) + Ca(OH)₂ → Mg(OH)_2(pp) + CaCl_2(aq)

Physical

Magnesium chloride is a white hygroscopic solid, soluble in water but poorly soluble in organic solvents, such as ethanol.

Availability

Magnesium chloride is available as tofu coagulant, more exactly as "Nigari flakes" or "Nigari salt". Some formulations also have magnesium sulfate.

Magnesium chloride sometimes occurs naturally as the mineral bischofite.

Preparation

Magnesium chloride can be prepared by reacting hydrochloric acid with magnesium metal, though this reaction is highly exothermic and magnesium metal is expensive.

Mg + 2 HCl → MgCl₂ + H₂

Magnesium carbonate or magnesium hydroxide are much safer to use and much cheaper.

MgCO₃ + 2 HCl → MgCl₂ + H₂O + CO₂

Mg(OH)₂ + 2 HCl → MgCl₂ + 2 H₂

A cheaper way involves the reaction of magnesium sulfate (Epsom salt) with calcium chloride.

MgSO₂ + CaCl₂ → MgCl₂ + CaSO₂

The resulting calcium sulfate is filtered off and the magnesium chloride solution is gently heated at 100 °C to remove the water. Since a small amount will hydrolyze, adding hydrogen chloride gas/conc. hydrochloric acid will regenerate the magnesium chloride. Magnesium carbonate can also be used instead of Epsom salt, but since it's very poorly soluble, the reaction needs lengthy boiling under reflux (similarly to converting barium sulfate to carbonate).

To prepare anhydrous magnesium chloride, the hexahydrate is heated in a stream of hydrogen chloride.

Projects

• Make elemental magnesium (electrolysis of molten MgCl₂ at temperatures over 714 °C, or of an eutectic mixture of MgCl₂-KCl-NaCl above 475 °C)
• Home-made desiccator
• Make tofu

Handling

Safety

Magnesium chloride is deliquescent and its anhydrous form may cause irritations on contact with skin, eyes or mouth.

Storage

Because of its hygroscopicity, magnesium chloride must be stored in an air-tight container.

Disposal

Magnesium chloride can be safely poured down the drain.

References

Relevant Sciencemadness threads

• failed attempt for magnesium chloride.
• Magnesium Chloride to Magnesium Metal