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Strontium hydroxide
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3D model (JSmol)
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| ChemSpider | |
| ECHA InfoCard | 100.038.501 |
| EC Number |
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| 847042 | |
PubChem CID
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CompTox Dashboard (EPA)
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| Properties | |
| Sr(OH)2 | |
| Molar mass | 121.63 g/mol (anhydrous) 139.65 g/mol (monohydrate) 265.76 g/mol (octahydrate) |
| Appearance | prismatic colourless crystals deliquescent |
| Density | 3.625 g/cm3 (anhydrous) 1.90 g/cm3 (octahydrate) |
| Melting point | 535 °C (995 °F; 808 K) (anhydrous, 375K for octahydrate) |
| Boiling point | 710 °C (1,310 °F; 983 K) decomposes (anhydrous) |
| 0.41 g/100 mL (0 °C) 1.77 g/100 mL (40 °C) 21.83 g/100 mL (100 °C) [1] | |
| Solubility | insoluble in acetone soluble in acid, NH4Cl |
| Basicity (pKb) | 0.3 (first OH–), 0.83 (second OH–)[2] |
| −40.0·10−6 cm3/mol | |
| Structure | |
| tetragonal (octahydrate) | |
| Hazards | |
| NFPA 704 (fire diamond) | |
| Flash point | Non-flammable |
| Related compounds | |
Other anions
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Strontium oxide Strontium peroxide |
Other cations
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Beryllium hydroxide Magnesium hydroxide Calcium hydroxide Barium hydroxide |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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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, or octahydrate form.
Preparation
[edit]Because Sr(OH)2 is 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). 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 cold water and dried.[3]
Applications
[edit]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 is undesirable. Strontium hydroxide absorbs carbon dioxide from the air to form strontium carbonate.
Safety
[edit]Strontium hydroxide is a severe skin, eye and respiratory irritant. It is harmful if swallowed.
References
[edit]- ^ Pradyot Patnaik. Handbook of Inorganic Chemicals. McGraw-Hill, 2002, ISBN 0-07-049439-8
- ^ "Sortierte Liste: pKb-Werte, nach Ordnungszahl sortiert. - Das Periodensystem online" (in German).
- ^ Brauer, Georg (1963). Handbook Of Preparative Inorganic Chemistry. Academic Press. p. 935.
External links
[edit]Grokipedia
Strontium hydroxide
View on Grokipediafrom Grokipedia
Properties
Physical properties
Strontium hydroxide occurs as prismatic, colorless, deliquescent crystals.[1] The compound exists in anhydrous, monohydrate, and octahydrate forms, with molar masses of 121.63 g/mol, 139.65 g/mol, and 265.76 g/mol, respectively.[5][2][6] The density of the anhydrous form is 3.625 g/cm³, while the octahydrate has a density of 1.90 g/cm³.[1][7] The anhydrous form melts at 535 °C and decomposes at 710 °C, whereas the octahydrate melts at approximately 100 °C (375 K).[1][7]| Property | Anhydrous | Octahydrate |
|---|---|---|
| Density (g/cm³) | 3.625 | 1.90 |
| Melting point (°C) | 535 (decomposes at 710) | 100 |
Chemical properties
Strontium hydroxide, Sr(OH)₂, functions as a strong base in aqueous solutions, fully dissociating into Sr²⁺ and 2 OH⁻ ions, which results in highly alkaline conditions with a pH typically ranging from 13 to 14 depending on concentration.[1][9] This dissociation enables its use in neutralization reactions and contributes to its corrosive nature toward acids and certain salts.[1] The compound exhibits strong reactivity with acids, undergoing neutralization to form the corresponding strontium salt and water; for instance, it reacts with hydrochloric acid according to the equation:
[1]
It also reacts vigorously with ammonium salts, such as ammonium chloride, liberating ammonia gas in a double displacement reaction:
[10] This exothermic process is commonly employed to generate ammonia in laboratory settings.
Upon heating, strontium hydroxide undergoes thermal decomposition, breaking down into strontium oxide and water vapor, as represented by:
This occurs at approximately 710°C for the anhydrous form, with the reaction proceeding more readily in the absence of moisture.[1]
Strontium hydroxide is deliquescent, readily absorbing atmospheric moisture to form hydrated crystals, which underscores its hygroscopic behavior and necessitates storage in dry conditions to prevent degradation.[1]
Structure and hydrates
Crystal structure
Strontium hydroxide is an ionic compound composed of Sr²⁺ cations and OH⁻ anions organized in a three-dimensional lattice. The anhydrous form adopts an orthorhombic crystal system, characterized by the space group Pnma (No. 62).[11][1] This structure features four formula units per unit cell, with the Sr²⁺ ions positioned in a distorted environment that reflects the compound's ionic bonding nature.[11] In the crystal lattice, each Sr²⁺ cation is coordinated by seven OH⁻ anions, forming a capped octahedral polyhedron around the metal center. The Sr-O bond distances in this coordination sphere average approximately 2.60 Å, contributing to the overall stability of the anhydrous phase. This sevenfold coordination is influenced by the relatively large size of the Sr²⁺ ion, which allows for an expanded coordination sphere compared to smaller alkaline earth analogs. The lattice parameters of anhydrous Sr(OH)₂ are notably larger than those of calcium hydroxide, Ca(OH)₂, primarily due to the greater ionic radius of Sr²⁺ (1.18 Å in sixfold coordination) relative to Ca²⁺ (1.00 Å in sixfold coordination). While Ca(OH)₂ exhibits a trigonal structure with sixfold coordination, the orthorhombic arrangement in Sr(OH)₂ accommodates the increased interionic distances, highlighting the role of cation size in dictating structural motifs among group 2 hydroxides.[12]Hydrated forms
Strontium hydroxide forms several hydrated phases, with the monohydrate and octahydrate being the most prominent. The octahydrate, Sr(OH)₂·8H₂O, is stable at room temperature under normal conditions and crystallizes from aqueous solutions. It exhibits a density of 1.90 g/cm³ and dehydrates at approximately 375 K.[2] The monohydrate, Sr(OH)₂·H₂O, is stable above approximately 85 °C (358 K), though it can partially decompose to the anhydrous form upon prolonged evacuation or heating. It is typically obtained through hydration processes conducted at relatively higher temperatures compared to the octahydrate.[13] The octahydrate, Sr(OH)₂·8H₂O, represents the form stable in hydrated environments up to 85 °C. It crystallizes in the tetragonal space group P4/ncc.[14] In its crystal structure, the Sr²⁺ ions are coordinated by eight water molecules in a square antiprism arrangement, forming double layers separated by hydroxide ions along the c-axis, with extensive hydrogen bonding stabilizing the lattice.[14] Phase transitions between these hydrates occur with temperature changes, reflecting their thermal stability ranges. The octahydrate is the stable phase up to approximately 85 °C (358 K); above this temperature, the monohydrate is favored, losing its water content around 110 °C to yield the anhydrous form; the anhydrous form predominates above 110 °C.[15][13] These transitions highlight the compound's sensitivity to hydration levels and thermal conditions, influencing its practical handling.Preparation
Laboratory methods
Strontium hydroxide can be prepared in the laboratory by precipitation from soluble strontium salts, such as strontium nitrate, using a strong base like sodium hydroxide. The reaction proceeds as follows:
This method involves dissolving strontium nitrate in water and slowly adding an aqueous solution of sodium hydroxide until precipitation is complete, resulting in fine white crystals of strontium hydroxide.[2] The precipitate is then filtered, washed with cold water to remove sodium nitrate impurities, and dried.[8]
An alternative laboratory synthesis involves the hydration of strontium oxide with water. The reaction is:
Strontium oxide is typically exposed to water vapor under controlled humidity conditions or added cautiously to liquid water, as the reaction is exothermic. This approach is suitable for small-scale preparations and yields strontium hydroxide directly, though care must be taken to avoid excessive heat buildup.[1]
Purification of the crude strontium hydroxide, often obtained as the octahydrate, can be achieved by recrystallization from hot water to isolate the monohydrate form, Sr(OH)₂·H₂O. The solid is dissolved in approximately 2.2 mL of hot water per gram and the solution cooled to 0°C, promoting crystallization of the purified monohydrate.[1][13]
Yields for the precipitation method are near quantitative due to the low solubility of strontium hydroxide in cold water (0.41 g/100 mL at 0°C), though filtration is essential to separate the product from soluble byproducts and ensure high purity.[2] The hydration method also provides high yields but may require additional drying steps to achieve the desired hydrate form.[8]
Industrial production
Strontium hydroxide is produced industrially primarily by the hydration of strontium oxide, which is obtained by reductive roasting of celestite ore (SrSO₄) with a reducing agent such as coke at 1000–1350 °C, converting the sulfate to oxide while releasing reduced sulfur compounds such as SO₂. The resulting strontium oxide is then hydrated with water under boiling conditions (around 90 °C) or under pressure at elevated temperatures up to 400 °C: SrO + H₂O → Sr(OH)₂. This method allows for efficient extraction from the primary mineral source, celestite, which is abundant but requires beneficiation to >90% purity prior to processing.[16] An alternative industrial route involves heating strontium carbonate (SrCO₃) or strontium sulfide (SrS) with steam at temperatures around 500–600 °C:
This process directly yields strontium hydroxide and is used in some facilities processing strontium compounds.[1][8]
Strontium hydroxide is generally manufactured as a byproduct during broader strontium compound processing, with global annual output on the order of thousands of tons, reflecting its niche role compared to dominant products like strontium carbonate. U.S. imports of strontium oxide, hydroxide, and peroxide totaled about 67 metric tons in 2019, with overall imports of strontium compounds (in strontium content) estimated at 3,700 metric tons in 2023, indicating limited large-scale domestic production.[17][18]
Production costs are influenced primarily by the supply of celestite ore, which accounts for much of the raw material expense, and the energy-intensive steps involved in high-temperature roasting and pressurized hydration. Energy costs for calcination and reduction can represent a significant portion of overall expenses, particularly in regions with volatile fuel prices.[17]