Caesium hydroxide

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Cesium hydroxide
CAS number 21351-79-1 YesY
ChemSpider 56494 YesY
EC-number 244-344-1
UN number 2682
ChEBI CHEBI:33988 YesY
RTECS number FK9800000
Jmol-3D images Image 1
Molecular formula CsOH
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]
Solubility in water 300 g/100 mL at 30 °C
Solubility Soluble in ethanol[1]
Basicity (pKb) -1.76[2]
heat capacity
69.9 J·mol-1·K-1[4]
Std molar
104.2 J·K−1·mol−1
Std enthalpy of
−416.2 kJ·mol-1
EU Index Not listed
Flash point Not flammable
LD50 570 mg/kg (oral, rat)[5]
Related compounds
Other anions Caesium oxide
Caesium fluoride
Other cations Lithium hydroxide
Sodium hydroxide
Potassium hydroxide
Rubidium hydroxide
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references

Cesium hydroxide (CsOH) is a chemical compound consisting of an ion of cesium and a hydroxide ion. It is a strong base (pKb=-1.76), much like 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, cesium hydroxide is extremely hygroscopic. Laboratory cesium 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.

However, this compound is not usually used in experiments as the extraction of cesium is very expensive and the fact that it behaves very much like rubidium hydroxide and potassium hydroxide although it is more reactive than they are.

Cesium hydroxide can be obtained by the following chemical reaction:

2 Cs + 2 H2O → 2 CsOH + H2

The above reaction occurs explosively with enough force to shatter a Pyrex beaker. Cesium metal will react with ice above −116 °C.


  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. ^
  3. ^
  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. ^

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