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Strontium hydroxide

Chemical compound From Wikipedia, the free encyclopedia

Strontium hydroxide, Sr(OH)2, is a caustic alkali composed of one strontium ion and two hydroxide ions. It is synthesized by combining a strontium salt with a strong base. Sr(OH)2 exists in anhydrous, monohydrate, heptahydrate, and octahydrate form.

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Strontium hydroxide
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.038.501 Edit this at Wikidata
EC Number
  • 242-367-1
847042
UNII
  • InChI=1S/2H2O.Sr/h2*1H2;/q;;+2/p-2 checkY
    Key: UUCCCPNEFXQJEL-UHFFFAOYSA-L checkY
  • InChI=1/2H2O.Sr/h2*1H2;/q;;+2/p-2
    Key: UUCCCPNEFXQJEL-NUQVWONBAP
  • [Sr+2].[OH-].[OH-]
Properties[1]
Sr(OH)2
Molar mass
  • 121.63 g⋅mol−1 (anhydrous)
  • 139.65 g⋅mol−1 (monohydrate)
  • 265.76 g⋅mol−1 (octahydrate)
Appearance colourless orthorhombic crystals, hygroscopic
Density
  • 3.625 g/cm3 (anhydrous)
  • 1.90 g/cm3 (octahydrate)
Melting point anhydrous: 535 °C (995 °F; 808 K)
  • monohydrate: 450 °C (842 °F)) (decomposes to anhydrous)[2]
  • octahydrate: 102 °C (216 °F) (decomposes to heptahydrate)[2]
Boiling point 710 °C (1,310 °F; 983 K)
  • decomposes (anhydrous)
  • dehydration above 850 °C (1,560 °F) produces SrO[2]: 932 
2.25 g/100 g
Basicity (pKb)
−40.0×10−6 cm3/mol
Structure[3]
Orthorhombic
Pmc21 [26]
mm2
a = 3.997 Å, b = 6.078 Å, c = 10.072 Å
α = 90°, β = 90°, γ = 90°
244.677 Å3
4
Thermochemistry[1]
−959.0 kJ⋅mol−1
Enthalpy of fusion (ΔfH⦵fus)
 23 kJ⋅mol−1
Hazards
NFPA 704 (fire diamond)
[citation needed]
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 1: Normally stable, but can become unstable at elevated temperatures and pressures. E.g. calciumSpecial hazards (white): no code
1
0
1
Related compounds
Other anions
Other cations
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Preparation

Because Sr(OH)2 is only slightly soluble in cold water, its preparation can be easily carried out by the addition of a strong base such as NaOH or KOH drop by drop to a solution of any soluble strontium salt, most commonly Sr(NO3)2 (strontium nitrate), which forms the octahydrate. This must be done in the absence of CO2 to prevent formation of the nearly insoluble carbonate which would complicate purification:

Sr(NO3)2·4H2O + 2 KOH + 4 H2O → Sr(OH)2·8H2O + 2 KNO3

The Sr(OH)2 will precipitate out as a fine white powder. From here, the solution is filtered, and the Sr(OH)2 is washed with a large excess of ice cold water and dried.[2]

The anhydrous form or any of the hydrates may be prepared by adding one molar equivalent of water to strontium oxide (SrO). The hydrates may be prepared by adding the required amount of water (one, seven, or eight more molar equivalents) to the anhydrous form.[2]

Applications

Strontium hydroxide is used chiefly in the refining of beet sugar and as a stabilizer in plastic. It may be used as a source of strontium ions when the chlorine from strontium chloride (SrCl2) is undesirable. Strontium hydroxide absorbs carbon dioxide (CO2) from the air to form strontium carbonate (SrCO3).

Safety

Strontium hydroxide is a severe skin, eye and respiratory irritant. It is harmful if swallowed.

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