Potassium hydroxide

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Potassium hydroxide
Other names Potash lye
CAS number 1310-58-3
RTECS number TT2100000
Molecular formula KOH
Molar mass 56.10564 g/mol
Appearance white solid,
Density 2.044 g/cm³, solid
Melting point

360 °C

Boiling point

1320 °C

Solubility in water 1100 g/L (25 °C)
Basicity (pKb) -2.29
Crystal structure monoclinic
EU classification Corrosive (C)
R-phrases R22, R35
S-phrases (S1/2), S26, S36/37/39, S45
Flash point non flammable
Related Compounds
Other anions Potassium oxide; Potassium peroxide; Potassium superoxide
Other cations Lithium hydroxide; Sodium hydroxide; Rubidium hydroxide; Caesium hydroxide
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)

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The chemical compound potassium hydroxide (KOH), sometimes known as caustic potash, potassa, potash lye, and potassium hydrate, is a metallic base. It is very alkaline and is a "strong base", along with sodium hydroxide, lithium hydroxide, calcium hydroxide, barium hydroxide and strontium hydroxide.


Pure potassium hydroxide is a colorless, highly hygroscopic, solid crystalline compound, having density of about 2.04 g/cm3, readily soluble in water (1 g KOH dissolves in 0.5 g water) and lower alcohols (methanol, ethanol, propanols; solubility in ethanol being about 1 g KOH/2.5 mL EtOH), as well as other polar solvents. The dissolution in water is strongly exothermic, producing substantial amounts of energy in form of heat, leading to temperature rise, sometimes up to boiling point and over; concentrated aqueous solutions are called potassium lyes. Potassium hydroxide forms solid hydrates, namely the monohydrate KOH·H2O, the dihydrate KOH·2H2O, and the tetrahydrate KOH·4H2O; it is used therefore as a highly intensive desiccant agent, e.g. for drying liquid amines or their solutions in indifferent, nonpolar solvents (such as hydrocarbons). It is a highly basic compound, forming strongly alkali solutions in water and other polar solvents, capable of deprotonating many acids, even weak ones, and decompose some inorganic as well as organic materials (e.g. dissolution and hydrolysis of broken glass or fats in concentrated KOH solutions). It is an important industrial chemical, used to manufacture many industrial as well as commercial goods and products, for example, most potassium salts; it's also an important laboratory chemical and reagent, again, used to prepare potassium salts, to neutralize acids, further as basic standard in analytics and many more applications. As every strong base/alkali, potassium hydroxide is strongly corrosive, both towards inorganic as well as organic materials, including living tissues; care must be therefore taken, when handling the substance and its solutions. Its corrosivity is sometimes used in cleaning and disinfection of resistant surfaces and materials.[1]


Of historical relevance is the old method of boiling a solution of potassium carbonate (potash) with calcium hydroxide (slaked lime); the ion transfer reaction takes place, because forming calcium carbonate is less soluble than lime, precipitating out of the reaction mixture:

Ca(OH)2 (s), (aq) + K2CO3 (aq) → ↓CaCO3 (s) + 2 KOH (aq)

precipitated calcium carbonate was than filtered out and the resulting KOH solution boiled down, leaving solid potassium hydroxide ("calcinated or caustic potash"). This method, using potash extracted from wood ashes and slaked lime was known probably already in antique times and was the most important method of producing potassium hydroxide until the late 19th century, when it was largely replaced by the modern method of electrolysis of potassium chloride solutions, analogous to the method of manufacturing sodium hydroxide:

2 K+ (aq) + 2H2O (l) + 2e → ↑H2 (g) + 2 KOH (aq)

Hydrogen gas forms as by-product on the cathode; concurrently, an anodic oxidation of the chloride ion takes place:

2 Cl — 2e → ↑Cl2 (g),

forming chlorine gas as another byproduct. Separation of the anodic and cathodic spaces in the electrolysis cell is essential for this process. For details, see chloralkali process.[2]


See also


  1. Römpp Chemie-Lexikon, 9th Ed. (in German)
  2. Römpp Chemie-Lexikon, 9th Ed. (in german)
  3. http://www.potassium-hydroxide.com
  4. http://www.weichtiere.at/Mollusks/Schnecken/weinberg.html
  5. http://www.hydroponicsearch.com/Explore_the_Science_of_Hydroponics/Plants/Potassium_hydroxide/
  6. http://dermatology.about.com/library/bldefpothyrox.htm
  7. http://www.jabfm.org/cgi/content/full/18/6/561
  8. http://www.p2pays.org/ref%5C02/01258.pdf
  9. http://www.codexalimentarius.net/gsfaonline/additives/details.html?id=311
  10. http://biodieselmagazine.com/article.jsp?article_id=462
  11. http://www.howtobrew.com/section1/chapter2-2-1.html
  12. http://www.powerstream.com/BatteryFAQ.html
  13. http://snf.stanford.edu/Materials/ChemFiles/KOHEtch.html
  14. http://dx.doi.org/10.1016/j.sna.2003.11.013
  15. http://www3.interscience.wiley.com/cgi-bin/abstract/112577341/ABSTRACT

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| group5 = Clinical Trials Involving Potassium hydroxide | list5 = Ongoing Trials on Potassium hydroxide at Clinical Trials.govTrial results on Potassium hydroxideClinical Trials on Potassium hydroxide at Google

| group6 = Guidelines / Policies / Government Resources (FDA/CDC) Regarding Potassium hydroxide | list6 = US National Guidelines Clearinghouse on Potassium hydroxideNICE Guidance on Potassium hydroxideNHS PRODIGY GuidanceFDA on Potassium hydroxideCDC on Potassium hydroxide

| group7 = Textbook Information on Potassium hydroxide | list7 = Books and Textbook Information on Potassium hydroxide

| group8 = Pharmacology Resources on Potassium hydroxide | list8 = AND (Dose)}} Dosing of Potassium hydroxideAND (drug interactions)}} Drug interactions with Potassium hydroxideAND (side effects)}} Side effects of Potassium hydroxideAND (Allergy)}} Allergic reactions to Potassium hydroxideAND (overdose)}} Overdose information on Potassium hydroxideAND (carcinogenicity)}} Carcinogenicity information on Potassium hydroxideAND (pregnancy)}} Potassium hydroxide in pregnancyAND (pharmacokinetics)}} Pharmacokinetics of Potassium hydroxide

| group9 = Genetics, Pharmacogenomics, and Proteinomics of Potassium hydroxide | list9 = AND (pharmacogenomics)}} Genetics of Potassium hydroxideAND (pharmacogenomics)}} Pharmacogenomics of Potassium hydroxideAND (proteomics)}} Proteomics of Potassium hydroxide

| group10 = Newstories on Potassium hydroxide | list10 = Potassium hydroxide in the newsBe alerted to news on Potassium hydroxideNews trends on Potassium hydroxide</small>

| group11 = Commentary on Potassium hydroxide | list11 = Blogs on Potassium hydroxide

| group12 = Patient Resources on Potassium hydroxide | list12 = Patient resources on Potassium hydroxideDiscussion groups on Potassium hydroxidePatient Handouts on Potassium hydroxideDirections to Hospitals Treating Potassium hydroxideRisk calculators and risk factors for Potassium hydroxide

| group13 = Healthcare Provider Resources on Potassium hydroxide | list13 = Symptoms of Potassium hydroxideCauses & Risk Factors for Potassium hydroxideDiagnostic studies for Potassium hydroxideTreatment of Potassium hydroxide

| group14 = Continuing Medical Education (CME) Programs on Potassium hydroxide | list14 = CME Programs on Potassium hydroxide

| group15 = International Resources on Potassium hydroxide | list15 = Potassium hydroxide en EspanolPotassium hydroxide en Francais

| group16 = Business Resources on Potassium hydroxide | list16 = Potassium hydroxide in the MarketplacePatents on Potassium hydroxide

| group17 = Informatics Resources on Potassium hydroxide | list17 = List of terms related to Potassium hydroxide