Magnesium chloride

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Magnesium chloride
Names
IUPAC name
Magnesium chloride
Systematic IUPAC name
Magnesium chloride
Other names
Nigari salt
Identifiers
Jmol-3D images Image
Properties
MgCl2
Molar mass 95.211 g/mol (anhydrous)
203.31 g/mol (hexahydrate)
Appearance white or colorless crystalline 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)
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 slightly soluble in acetone, pyridine
Solubility in ethanol 7.4 g/100 mL (30 °C)
Thermochemistry
89.88 J/mol K
-641.1 kJ/mol
Hazards
Safety data sheet ICSC 0764
Flash point Non-flammable
Lethal dose or concentration (LD, LC):
2800 mg/kg (oral, rat)
Related compounds
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:

MgCl2(aq) + Ca(OH)2 → Mg(OH)2(pp) + CaCl2(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".

Magnesium chloride sometimes occurs naturally as the mineral bischofite.

Preparation

Magnesium chloride can be prepared by reacting hydrochloric acid with magnesium or magnesium carbonate.

A cheaper way involves the reaction of magnesium sulfate (Epsom salt) with calcium chloride. 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, injecting dry hydrogen chloride gas 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).

Projects

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

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