Magnesium hydroxide

 

Magnesium hydroxide

Chemical formula	Mg(OH)2
Molar Mass(g/mol)	58.3
Density(g/cc)	2.34
Melting Point(°C)	350
NFPA 704	0 1 0
Thermal Decomposition	Magnesium hydroxide 350°C MgO

Magnesium hydroxide is a close analogue of calcium hydroxide.

Uses

Primary

• As an aqueous suspension/solution, it is known as Milk of Magnesia, which has medicinal properties:
  • as an antacid
  • as a laxative
• as a fire retardant

Production

Extraction

from seawater

• Add calcium oxide or calcium hydroxide to salt water (which contains Mg²⁺ ions). Calcium hydroxide being more soluble than magnesium hydroxide, the latter precipitates.

Synthesis

from soluble magnesium salts

1. Dissolve magnesium chloride or magnesium nitrate in distilled water
2. Add calcium oxide or calcium hydroxide

   CaO(s) + H₂O + MgCl₂(aq) → CaCl₂(aq) + MgOH(s)

   Ca(OH)₂(s) + Mg(NO₃)₂(aq) → Ca(NO₃)₂(aq) + Mg(OH)₂(s)