Caesium hydroxide

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Caesium hydroxide
Cesium hydroxide monohydrate.jpg
Other names
Caesium hydrate
3D model (Jmol)
ECHA InfoCard 100.040.298
EC Number 244-344-1
RTECS number FK9800000
UN number 2682
Molar mass 149.912 g/mol
Appearance Whitish-yellow deliquescent crystals
Density 3.675 g/cm3
Melting point 272 °C (522 °F; 545 K)[3]
300 g/100 mL at 30 °C
Solubility Soluble in ethanol[1]
Basicity (pKb) −0.8[2](CsOH(aq) = Cs+ + OH)
69.9 J·mol−1·K−1[4]
104.2 J·K−1·mol−1
−416.2 kJ·mol−1
Safety data sheet ICSC 1592
Flash point Not flammable
Lethal dose or concentration (LD, LC):
570 mg/kg (oral, rat)[6]
US health exposure limits (NIOSH):
PEL (Permissible)
REL (Recommended)
TWA 2 mg/m3[5]
IDLH (Immediate danger)
Related compounds
Other anions
Caesium oxide
Caesium fluoride
Other cations
Lithium hydroxide
Sodium hydroxide
Potassium hydroxide
Rubidium 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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Infobox references

Caesium hydroxide (CsOH) is a chemical compound consisting of an ion of caesium and a hydroxide ion. It is a strong base (pKb=-1.76), much like the other alkali metal hydroxides such as sodium hydroxide and potassium hydroxide. In fact, caesium hydroxide is powerful enough to quickly corrode through glass.

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.


  1. ^ Lide, David R. (1998), Handbook of Chemistry and Physics (87 ed.), Boca Raton, FL: CRC Press, pp. 4–51, ISBN 0-8493-0594-2 
  2. ^ Popov, K.; et al. (2002). "7Li, 23Na, 39K and 133Cs NMR comparative equilibrium study of alkali metal cation hydroxide complexes in aqueous solutions. First numerical value for CsOH formation". Inorganic Chemistry Communications. 5 (3): 223–225. Retrieved 2017-02-19. 
  3. ^ "ICSC 1592 - Cesium Hydroxide". 
  4. ^ Lide, David R. (1998), Handbook of Chemistry and Physics (87 ed.), Boca Raton, FL: CRC Press, pp. 5–14, ISBN 0-8493-0594-2 
  5. ^ a b c "NIOSH Pocket Guide to Chemical Hazards #0111". National Institute for Occupational Safety and Health (NIOSH). 
  6. ^ Chambers, Michael. "ChemIDplus - 21351-79-1 - HUCVOHYBFXVBRW-UHFFFAOYSA-M - Cesium hydroxide - Similar structures search, synonyms, formulas, resource links, and other chemical information.". 

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