:Caesium hydroxide

{{Short description|Chemical compound}}

{{Chembox

| Watchedfields = changed

| verifiedrevid = 443494816

| Name =

| OtherNames = Cesium hydrate

| ImageFile = Cesium hydroxide monohydrate.jpg

| Section1 = {{Chembox Identifiers

| InChI = 1/Cs.H2O/h;1H2/q+1;/p-1

| ChEBI_Ref = {{ebicite|correct|EBI}}

| ChEBI = 33988

| SMILES = [OH-].[Cs+]

| InChIKey = HUCVOHYBFXVBRW-REWHXWOFAG

| StdInChI_Ref = {{stdinchicite|correct|chemspider}}

| StdInChI = 1S/Cs.H2O/h;1H2/q+1;/p-1

| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}

| StdInChIKey = HUCVOHYBFXVBRW-UHFFFAOYSA-M

| CASNo = 21351-79-1

| CASNo_Ref = {{cascite|correct|CAS}}

| EC_number = 244-344-1

| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}

| ChemSpiderID = 56494

| RTECS = FK9800000

| UNNumber = 2682

| PubChem = 62750

| UNII = 458ZFZ6235

}}

| Section2 = {{Chembox Properties

| Formula = CsOH

| MolarMass = 149.912 g/mol

| Appearance = Whitish-yellow deliquescent crystals

| Density = 3.675 g/cm³

| MeltingPtC = 272

| MeltingPt_ref = {{cite web|url=http://www.inchem.org/documents/icsc/icsc/eics1592.htm|title=ICSC 1592 - Cesium Hydroxide}}

| Solubility = 300 g/100 mL at 30 °C

| SolubleOther = Soluble in ethanol

{{Citation

| last = Lide

| first = David R.

| year = 1998

| title = Handbook of Chemistry and Physics

| edition = 87

| publication-place = Boca Raton, Florida

| publisher = CRC Press

| isbn = 0-8493-0594-2

| pages = 4–51

}}

| pKa = 15.76 {{cite web|url=http://www.periodensystem-online.de/index.php?show=list&id=acid&prop=pKb-Werte&sel=oz&el=92|title=Sortierte Liste: pKb-Werte, nach Ordnungszahl sortiert. – Das Periodensystem online}}

}}

| Section3 = {{Chembox Structure

| Coordination =

| CrystalStruct =

}}

| Section4 = {{Chembox Thermochemistry

| DeltaHf = −416.2 kJ·mol⁻¹

| Entropy = 104.2 J·K⁻¹·mol⁻¹

| HeatCapacity = 69.9 J·mol⁻¹·K⁻¹

{{Citation

| last = Lide

| first = David R.

| year = 1998

| title = Handbook of Chemistry and Physics

| edition = 87

| publication-place = Boca Raton, Florida

| publisher = CRC Press

| isbn = 0-8493-0594-2

| pages = 5–14

}}

}}

| Section7 = {{Chembox Hazards

| NFPA-H = 3

| NFPA-F = 0

| NFPA-R = 1

| NFPA-S = ALK

| ExternalSDS = [http://www.inchem.org/documents/icsc/icsc/eics1592.htm ICSC 1592]

| FlashPt = Not flammable

| LD50 = 570 mg/kg (oral, rat)Gigiena Truda i Professional'nye Zabolevaniya. Labor Hygiene and Occupational Diseases., 21(1)(29), 1977

| PEL = none{{PGCH|0111}}

| REL = TWA 2 mg/m³

| IDLH = N.D.

| GHSSignalWord = Danger

| GHSPictograms = {{GHS05}}{{GHS08}}

| HPhrases = {{H-phrases|302|314|361|373}}

| PPhrases = {{P-phrases|201|202|260|264|270|280|281|301+312|301+330+331|303+361+353|304+340|305+351+338|308+313|310|314|321|330|363|405|501}}

}}

| Section8 = {{Chembox Related

| OtherAnions = Caesium oxide
Caesium fluoride

| OtherCations = Lithium hydroxide
Sodium hydroxide
Potassium hydroxide
Rubidium hydroxide

}}

}}

Caesium hydroxide is a strong base (pK_a= 15.76) containing the highly reactive alkali metal caesium, much like the other alkali metal hydroxides such as sodium hydroxide and potassium hydroxide. It is the strongest of the five alkali metal hydroxides.{{Cite book |last1=Considine |first1=Douglas M. |url=https://books.google.com/books?id=t4jjBwAAQBAJ&pg=PA605 |title=Van Nostrand's Scientific Encyclopedia |last2=Considine |first2=Glenn D. |date=2013-12-11 |publisher=Springer Science & Business Media |isbn=978-1-4757-6918-0 |language=en}} Fused caesium hydroxide has applications in bringing glass samples into a solution for analytical purposes in the commercial glass industry and a defense waste processing facility as it is able to dissolve glass by attacking its silica framework. The melting process is carried out in a nickel or zirconium crucible.{{Cite web |last1=Coleman |first1=C.J |last2=Spencer |first2=W.A. |date=April 1998 |title=CsOH is a very strong base that attacks the silica framework of glass under fusion conditions. Cesium Hydroxide Fusion Dissolution of Analytical Reference Glass-1 in Both Powder and Shard Form |url=https://digital.library.unt.edu/ark:/67531/metadc706521/m2/1/high_res_d/651640.pdf |publisher=Westinghouse Savannah River Company |quote=CsOH is a very strong base that attacks the silica framework of glass under fusion conditions.}} Caesium hydroxide fusion at 750°C produces complete dissolution of glass pellets.

Due to its high reactivity, caesium hydroxide is extremely hygroscopic. Laboratory caesium hydroxide is typically a hydrate.

It is an anisotropic etchant of silicon, exposing octahedral planes. This technique can form pyramids and regularly shaped etch pits for uses such as Microelectromechanical systems. It is known to have a higher selectivity to etch highly p-doped silicon than the more commonly used potassium hydroxide.

This compound is not commonly used in experiments due to the high extraction cost of caesium and its reactive behaviour. It acts in similar fashion to the compounds rubidium hydroxide and potassium hydroxide, although more reactive.