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Revision as of 13:55, 5 December 2011 editBeetstra (talk | contribs)Edit filter managers, Administrators172,031 edits Saving copy of the {{chembox}} taken from revid 460757792 of page Potassium_hydroxide for the Chem/Drugbox validation project (updated: '').  Latest revision as of 06:28, 7 October 2024 edit MasterTriangle12 (talk | contribs)Extended confirmed users1,290 edits →Safety: Filling out the safety section.Tag: Visual edit 
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{{Short description|Inorganic compound (KOH)}}
{{ambox | text = This page contains a copy of the infobox ({{tl|chembox}}) taken from revid of page ] with values updated to verified values.}}
{{chembox {{chembox
|Verifiedfields = changed
| verifiedrevid = 449453670
|Watchedfields = changed
| Name = Potassium hydroxide
|verifiedrevid = 464361974
| ImageFile = Potassium hydroxide.jpg
|Name = Potassium hydroxide
| ImageSize = 200px
| ImageName = pellets of potassium hydroxide |ImageFile1 = Potassium hydroxide.jpg
| ImageFile1 = Potassium-hydroxide-xtal-3D-vdW.png |ImageName1 = Pellets of potassium hydroxide
|ImageFile = Potassium-hydroxide-xtal-3D-vdW.png
| ImageSize1 = 200px
| ImageName1 = crystal structure of KOH |ImageName = Crystal structure of KOH
| IUPACName = Potassium hydroxide |ImageSize = 150px
|IUPACName = Potassium hydroxide
| OtherNames = Caustic potash<br/>Potash lye<br/>Potassia<br/>Potassium hydrate |OtherNames = {{Unbulleted list|Caustic potash|]|Potash lye|Potassia|Potassium hydrate|KOH}}
| Section1 = {{Chembox Identifiers |Section1={{Chembox Identifiers
| UNII_Ref = {{fdacite|correct|FDA}} |UNII_Ref = {{fdacite|correct|FDA}}
| UNII = WZH3C48M4T |UNII = WZH3C48M4T
| InChI = 1/K.H2O/h;1H2/q+1;/p-1 |InChI = 1/K.H2O/h;1H2/q+1;/p-1
| InChIKey = KWYUFKZDYYNOTN-REWHXWOFAT |InChIKey = KWYUFKZDYYNOTN-REWHXWOFAT
| ChEBI_Ref = {{ebicite|correct|EBI}} |ChEBI_Ref = {{ebicite|correct|EBI}}
| ChEBI = 32035 |ChEBI = 32035
| SMILES = . |SMILES = .
| StdInChI_Ref = {{stdinchicite|correct|chemspider}} |StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| StdInChI = 1S/K.H2O/h;1H2/q+1;/p-1 |StdInChI = 1S/K.H2O/h;1H2/q+1;/p-1
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}} |StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| StdInChIKey = KWYUFKZDYYNOTN-UHFFFAOYSA-M |StdInChIKey = KWYUFKZDYYNOTN-UHFFFAOYSA-M
| CASNo = 1310-58-3 |CASNo = 1310-58-3
| CASNo_Ref = {{cascite|correct|CAS}} |CASNo_Ref = {{cascite|correct|CAS}}
| PubChem = 6093213 |PubChem = 14797
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}} |ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| ChemSpiderID = 14113 |ChemSpiderID = 14113
| RTECS = TT2100000 |RTECS = TT2100000
| UNNumber = 1813 |UNNumber = 1813
| EINECS = 215-181-3 |EINECS = 215-181-3
}} }}
| Section2 = {{Chembox Properties |Section2={{Chembox Properties
| Formula = KOH |Formula = KOH
|K=1|O=1|H=1
| MolarMass = 56.1056 g/mol
| Appearance = white solid, ] |Appearance = white solid, ]
|Odor = odorless
| Density = 2.044 g/cm<sup>3</sup><ref name=crc/>
| Solubility = 1210 g/L (25 °C) <br> 1780 g/L (100 °C)<ref name=crc>{{RubberBible86th|page=4-80}}</ref> |Density = 2.044 g/cm<sup>3</sup> (20 °C)<ref name=crc/><br/> 2.12 g/cm<sup>3</sup> (25 °C)<ref name=chemister />
|Solubility = 85 g/100 mL (-23.2 °C)<br/> 97 g/100 mL (0 °C)<br/> 121 g/100 mL (25 °C)<br/> 138.3 g/100 mL (50 °C)<br/> 162.9 g/100 mL (100 °C)<ref name=crc>{{RubberBible86th|page=4-80}}</ref><ref name=sioc>{{cite book|last1 = Seidell|first1 = Atherton|last2 = Linke|first2 = William F.|year = 1952|title = Solubilities of Inorganic and Organic Compounds|publisher = Van Nostrand|url = https://books.google.com/books?id=k2e5AAAAIAAJ|access-date = 2014-05-29}}</ref>
| SolubleOther = soluble in ], ] <br> insoluble in ], liquid ]
|SolubleOther = soluble in ], ] <br/> insoluble in ], liquid ]
| MeltingPt = 406 °C<ref name=crc/>
| BoilingPt = 1327 °C<ref name=crc/> |Solubility2 = 55 g/100 g (28 °C)<ref name=chemister />
|Solvent2 = methanol
| pKa = 13.5 (0.1 M)
|Solubility3 = ~14 g / 100 g (28 °C)
| RefractIndex = 1.409
|Solvent3 = isopropanol
|MeltingPtC = 410
<ref>{{cite journal | last1=Otto | first1=H.W | last2=Seward | first2=R.P. | title=Phase equilibria in the potassium hydroxide-sodium hydroxide system. | journal=J. Chem. Eng. Data | volume=9 | pages=507–508 | url=https://doi.org/10.1021/je60023a009 | doi=10.1021/je60023a009 | year=1964 | issue=4 }}</ref> <ref>{{cite journal | last1=Seward | first1=R.P | last2=Martin | first2=K.E. | title=The melting point of potassium hydroxide. | journal=J. Am. Chem. Soc. | volume=71 | pages=3564–3565 | url=https://doi.org/10.1021/ja01178a530 | doi=10.1021/ja01178a530 | year=1949 | issue=10 }}</ref>
|BoilingPtC = 1327
|pKa = 14.7<ref>{{cite journal | last1=Popov | first1=K. | last2=Lajunen | first2=L.H.J. | last3=Popov | first3=A. | last4=Rönkkömäki | first4=H. | last5=Hannu-Kuure | first5=M. | last6=Vendilo | first6=A. | title=<sup>7</sup>Li, <sup>23</sup>Na, <sup>39</sup>K and <sup>133</sup>Cs NMR comparative equilibrium study of alkali metal cation hydroxide complexes in aqueous solutions. First numerical value for CsOH formation | journal=Inorganic Chemistry Communications | volume=3 | issue=5 | issn=1387-7003 | pages=223–225 | url=https://www.infona.pl//resource/bwmeta1.element.elsevier-40fb73c1-ba37-32e0-914e-b264c7c0539b | access-date=October 20, 2018 |doi=10.1016/S1387-7003(02)00335-0 |display-authors=1| year=2002 }}</ref>
|RefractIndex = 1.409 (20 °C)
|MagSus = &minus;22.0·10<sup>−6</sup> cm<sup>3</sup>/mol
}} }}
| Section3 = {{Chembox Structure |Section3={{Chembox Thermochemistry
|DeltaHf = -425.8 kJ/mol<ref name=chemister>{{cite web|url=http://chemister.ru/Database/properties-en.php?dbid=1&id=325|title=potassium hydroxide|website=chemister.ru|access-date=8 May 2018|url-status=live|archive-url=https://web.archive.org/web/20140518070658/http://chemister.ru/Database/properties-en.php?dbid=1&id=325|archive-date=18 May 2014}}</ref><ref name=b1>{{cite book| author = Zumdahl, Steven S.|title =Chemical Principles 6th Ed.| publisher = Houghton Mifflin Company| year = 2009| isbn = 978-0-618-94690-7|page=A22}}</ref>
| Coordination =
|Entropy = 79.32 J/mol·K<ref name=chemister /><ref name=b1 />
| CrystalStruct =rhombohedral
|DeltaGf = -380.2 kJ/mol<ref name=chemister />
|HeatCapacity = 65.87 J/mol·K<ref name=chemister />
}} }}
| Section7 = {{Chembox Hazards |Section4={{Chembox Hazards
| ExternalMSDS = |ExternalSDS =
|GHSPictograms = {{GHS05}}{{GHS07}}<ref name="sigma">{{Sigma-Aldrich|id=757551|name=Potassium hydroxide|accessdate=2014-05-18}}</ref>
| EUIndex = 019-002-00-8
|GHSSignalWord = Danger
| EUClass = Corrosive ('''C''')<br/>Harmful ('''Xn''')
|HPhrases = {{H-phrases|290|302|314}}<ref name="sigma" />
| RPhrases = {{R22}}, {{R35}}
|PPhrases = {{P-phrases|280|305+351+338|310}}<ref name="sigma" />
| SPhrases = {{S1/2}}, {{S26}}, {{S36/37/39}}, {{S45}}
| NFPA-H = 3 |NFPA-H = 3
| NFPA-F = 0 |NFPA-F = 0
| NFPA-R = 1 |NFPA-R = 1
| NFPA-O = |NFPA-S = ALK
| FlashPt = Non-flammable |FlashPt = nonflammable
|LD50 = 273 mg/kg (oral, rat)<ref>{{cite web|url=https://chem.nlm.nih.gov/chemidplus/rn/1310-58-3|title=ChemIDplus - 1310-58-3 - KWYUFKZDYYNOTN-UHFFFAOYSA-M - Potassium hydroxide - Similar structures search, synonyms, formulas, resource links, and other chemical information.|first=Michael|last=Chambers|website=chem.sis.nlm.nih.gov|access-date=8 May 2018|url-status=live|archive-url=http://archive.wikiwix.com/cache/20140812085045/https://chem.nlm.nih.gov/chemidplus/rn/1310-58-3|archive-date=12 August 2014}}</ref>
| LD50 = 273 mg/kg
|PEL = none<ref name=PGCH>{{PGCH|0523}}</ref>
|IDLH = N.D.<ref name=PGCH/>
|REL = C 2 mg/m<sup>3</sup><ref name=PGCH/>
}} }}
| Section8 = {{Chembox Related |Section5={{Chembox Related
| OtherAnions = ]<br/>] |OtherAnions = ]<br/>]
| OtherCations = ]<br/>]<br/>]<br/>] |OtherCations = ]<br/>]<br/>]<br/>]
| OtherCpds = ] |OtherCompounds = ]
}} }}
}} }}
'''Potassium hydroxide''' is an ] with the formula ]], and is commonly called '''caustic potash'''.

Along with ] (NaOH), KOH is a prototypical ]. It has many industrial and niche applications, most of which utilize its ] nature and its reactivity toward ]. An estimated 700,000 to 800,000 ]s were produced in 2005. KOH is noteworthy as the precursor to most soft and liquid ]s, as well as numerous potassium-containing chemicals. It is a white solid that is dangerously corrosive.<ref name=Ullmann>{{cite book| last1=Schultz | first1=Heinz | last2=Bauer | first2=Günter | last3=Schachl | first3=Erich | last4=Hagedorn | first4=Fritz | last5=Schmittinger | first5=Peter |title=Ullmann's Encyclopedia of Industrial Chemistry|publisher=Wiley-VCH|location=Weinheim, Germany| year=2005 | isbn=978-3-527-30673-2 | doi=10.1002/14356007.a22_039|chapter=Potassium Compounds}}</ref>

==Properties and structure==
KOH exhibits high ]. Because of this high stability and relatively low ], it is often melt-cast as pellets or rods, forms that have low surface area and convenient handling properties. These pellets become tacky in air because KOH is ]. Most commercial samples are ca. 90% pure, the remainder being water and carbonates.<ref name=Ullmann/> Its ] in water is strongly ]. Concentrated aqueous solutions are sometimes called potassium ]s. Even at high temperatures, solid KOH does not dehydrate readily.<ref>{{cite book|last1=Holleman|first1=A. F|last2=Wiberg|first2=E. |title=Inorganic Chemistry |publisher=Academic Press|location=San Diego|year=2001|isbn=978-0-12-352651-9}}</ref>

===Structure===
At higher temperatures, solid KOH ] in the ] ]. The {{OH-}} group is either rapidly or randomly disordered so that it is effectively a spherical ] of radius 1.53 Å (between {{chem2|Cl-}} and {{chem2|F-}} in size). At room temperature, the {{chem2|OH-}} groups are ordered and the environment about the {{chem2|K+}} centers is distorted, with {{chem2|K+\sOH-}} distances ranging from 2.69 to 3.15 Å, depending on the orientation of the OH group. KOH forms a series of crystalline ]s, namely the monohydrate {{chem2|KOH * ]}}, the dihydrate {{chem2|KOH * 2]}} and the tetrahydrate {{chem2|KOH * 4]}}.<ref>{{cite book |last=Wells |first=A.F. |year=1984 |title=Structural Inorganic Chemistry |location=Oxford |publisher=Clarendon Press |isbn=978-0-19-855370-0}}</ref>

==Reactions==
===Solubility and desiccating properties===
About 112 g of KOH ] in 100 mL water at room temperature, which contrasts with 100 g/100 mL for NaOH.<ref>{{cite book|last1 = Seidell|first1 = Atherton|last2 = Linke|first2 = William F.|year = 1952|title = Solubilities of Inorganic and Organic Compounds|publisher = Van Nostrand|url = https://books.google.com/books?id=k2e5AAAAIAAJ|access-date = 2014-05-29}}</ref> Thus on a molar basis, KOH is slightly more soluble than NaOH. Lower molecular-weight ]s such as ], ], and ]s are also excellent ]. They participate in an acid-base equilibrium. In the case of methanol the potassium ] (methylate) forms:<ref>{{Cite journal|last1=Platonov|first1=Andrew Y.|last2=Kurzin|first2=Alexander V.|last3=Evdokimov|first3=Andrey N.|date=2009|title=Composition of Vapor and Liquid Phases in the Potassium Hydroxide + Methanol Reaction System at 25 °С|journal=J. Solution Chem.|volume=39|issue=3|pages=335–342|doi=10.1007/s10953-010-9505-1|s2cid=97177429}}</ref>
: {{chem2|KOH + CH3OH -> CH3OK + H2O}}

Because of its high affinity for water, KOH serves as a ] in the laboratory. It is often used to dry basic solvents, especially ] and ].

===As a nucleophile in organic chemistry===
KOH, like NaOH, serves as a source of {{chem2|OH-}}, a highly ] anion that attacks ] in both inorganic and organic materials. Aqueous KOH ] ]s:
: {{chem2|KOH + RCOOR' -> RCOOK + R'OH}}

When R is a long chain, the product is called a ]. This reaction is manifested by the "greasy" feel that KOH gives when touched; ]s on the skin are rapidly converted to soap and ].

Molten KOH is used to displace ] and other ]s. The reaction is especially useful for ] ]s to give the corresponding ]s.<ref>{{OrgSynth|author = W. W. Hartman|title = ''p''-Cresol| collvol = 1|collvolpages = 175|prep = CV1P0175|year = 1923|volume = 3|pages = 37|doi = 10.15227/orgsyn.003.0037}}</ref>

===Reactions with inorganic compounds===
Complementary to its reactivity toward acids, KOH attacks ]s. Thus, SiO<sub>2</sub> is attacked by KOH to give soluble potassium silicates. KOH reacts with ] to give ]:
:{{chem2|KOH + CO2 -> KHCO3}}

==Manufacture==
Historically, KOH was made by adding ] to a strong solution of ] (slaked lime). The ] results in precipitation of solid ], leaving potassium hydroxide in solution:
:{{chem2|Ca(OH)2 + K2CO3 -> CaCO3 + 2 KOH}}

Filtering off the precipitated calcium carbonate and boiling down the solution gives potassium hydroxide ("calcinated or caustic potash"). This method of producing potassium hydroxide remained dominant until the late 19th century, when it was largely replaced by the current method of electrolysis of ] solutions.<ref name=Ullmann/> The method is analogous to the manufacture of ] (see ]):
:{{chem2|2 KCl + 2 H2O -> 2 KOH + Cl2 + H2}}

] gas forms as a byproduct on the ]; concurrently, an anodic oxidation of the ] ion takes place, forming ] gas as a byproduct. Separation of the anodic and cathodic spaces in the electrolysis cell is essential for this process.<ref name="auto">Römpp Chemie-Lexikon, 9th Ed. (in German)</ref>

==Uses==
KOH and NaOH can be used interchangeably for a number of applications, although in industry, NaOH is preferred because of its lower cost.

=== Catalyst for hydrothermal gasification process ===
In industry, KOH is a good catalyst for ] process. In this process, it is used to improve the yield of gas and amount of hydrogen in process. For example, production of ] from coal often produces much coking wastewater. In order to degrade it, ] water is used to convert it to the syngas containing ], ], ] and ]. Using ], we could separate various gases and then use ] technology to convert them to fuel.<ref>{{Cite journal |date=2020-01-13 |title=Gasification of coking wastewater in supercritical water adding alkali catalyst |journal=International Journal of Hydrogen Energy |language=en |volume=45 |issue=3 |pages=1608–1614 |doi=10.1016/j.ijhydene.2019.11.033 |issn=0360-3199|last1=Chen |first1=Fu |last2=Li |first2=Xiaoxiao |last3=Qu |first3=Junfeng |last4=Ma |first4=Jing |last5=Zhu |first5=Qianlin |last6=Zhang |first6=Shaoliang |s2cid=213336330 |doi-access=free |bibcode=2020IJHE...45.1608C }}</ref> On the other hand, the hydrothermal gasification process could degrade other waste such as sewage sludge and waste from food factories.

===Precursor to other potassium compounds===
Many potassium salts are prepared by neutralization reactions involving KOH. The potassium salts of ], ], ], ], and various silicates are prepared by treating either the oxides or the acids with KOH.<ref name=Ullmann/> The high solubility of ] is desirable in ]s.

===Manufacture of soft soaps===
The ] of ]s with KOH is used to prepare the corresponding "potassium ]", which are softer than the more common ]-derived soaps. Because of their softness and greater solubility, potassium soaps require less water to liquefy, and can thus contain more cleaning agent than liquefied sodium soaps.<ref>{{cite book |author=K. Schumann |author2=K. Siekmann |chapter=Soaps|title=Ullmann's Encyclopedia of Industrial Chemistry |year=2005|publisher=Wiley-VCH |location=Weinheim|doi=10.1002/14356007.a24_247|isbn=978-3527306732 }}</ref>

===As an electrolyte===
]
] potassium hydroxide is employed as the ] in ] based on ]-], ]-], and ]-]. Potassium hydroxide is preferred over ] because its solutions are more conductive.<ref>{{cite book |author=D. Berndt |author2=D. Spahrbier |chapter=Batteries |title=Ullmann's Encyclopedia of Industrial Chemistry |year=2005 |publisher=Wiley-VCH |location=Weinheim |doi=10.1002/14356007.a03_343|isbn=978-3527306732 }}</ref> The ] in the ] use a mixture of potassium hydroxide and sodium hydroxide.<ref>{{Cite web |title=Toyota Prius Hybrid 2010 Model Emergency Response Guide |publisher=Toyota Motor Corporation |year=2009 |url=http://www.toyota-tech.eu/HYBRID/ERG/EN/Prius%20ZVW30%20ERG.pdf |archive-url=https://web.archive.org/web/20120320175142/http://www.toyota-tech.eu/HYBRID/ERG/EN/Prius%20ZVW30%20ERG.pdf |archive-date=2012-03-20 |url-status=dead }}</ref> ] also use potassium hydroxide electrolyte.

===Food industry===
In food products, potassium hydroxide acts as a food thickener, pH control agent and food stabilizer. The ] considers it generally safe as a direct food ingredient when used in accordance with ].<ref>{{cite web |title=Compound Summary for CID 14797 - Potassium Hydroxide |url=https://pubchem.ncbi.nlm.nih.gov/compound/potassium_hydroxide |publisher=PubChem}}</ref> It is known in the ] system as '''E525'''.

===Niche applications===
Like sodium hydroxide, potassium hydroxide attracts numerous specialized applications, virtually all of which rely on its properties as a strong chemical base with its consequent ability to degrade many materials. For example, in a process commonly referred to as "chemical cremation" or "]", potassium hydroxide hastens the decomposition of soft tissues, both animal and human, to leave behind only the bones and other hard tissues.<ref>{{cite journal|last=Green|first=Margaret|title=A RAPID METHOD FOR CLEARING AND STAINING SPECIMENS FOR THE DEMONSTRATION OF BONE|journal=The Ohio Journal of Science|date=January 1952|volume=52|issue=1|pages=31–33|hdl=1811/3896}}</ref> ] wishing to study the fine structure of ] ] may use a 10% aqueous solution of KOH to apply this process.<ref>{{cite book |author=Thomas Eisner |title=For the Love of Insects |publisher=Harvard University Press |year=2003 |page=71}}</ref>

In chemical synthesis, the choice between the use of KOH and the use of NaOH is guided by the solubility or keeping quality of the resulting ].

The corrosive properties of potassium hydroxide make it a useful ingredient in agents and preparations that clean and ] surfaces and materials that can themselves resist ] by KOH.<ref name="auto"/>

KOH is also used for semiconductor chip fabrication (for example ]).

Potassium hydroxide is often the main active ingredient in chemical "cuticle removers" used in ] treatments.

Because aggressive bases like KOH damage the ] of the ] shaft, potassium hydroxide is used to chemically assist the removal of hair from animal hides. The hides are soaked for several hours in a solution of KOH and water to prepare them for the unhairing stage of the ] process. This same effect is also used to weaken human hair in preparation for shaving. Preshave products and some shave creams contain potassium hydroxide to force open the hair cuticle and to act as a hygroscopic agent to attract and force water into the hair shaft, causing further damage to the hair. In this weakened state, the hair is more easily cut by a razor blade.

Potassium hydroxide is used to identify some species of ]. A 3–5% aqueous solution of KOH is applied to the flesh of a mushroom and the researcher notes whether or not the color of the flesh changes. Certain species of ], ], ], and ]<ref>{{cite book|last1=Elix|first1=J.A.|title=Lichen Biology|last2=Stocker-Wörgötter|first2=Elfie|date=2008|publisher=]|isbn=978-0-521-69216-8|editor-last=Nash III|editor-first=Thomas H.|edition=2nd|location=New York|pages=118–119|chapter=Chapter 7: Biochemistry and secondary metabolites|author-link=John Alan Elix}}</ref> are identifiable based on this color-change reaction.<ref> {{webarchive|url=https://web.archive.org/web/20091015000955/http://www.mushroomexpert.com/macrochemicals.html |date=2009-10-15 }} at MushroomExpert.com</ref>

==Safety==
Potassium hydroxide is a ] alkali and its solutions range from irritating to skin and other tissue in low concentrations, to highly corrosive in high concentrations. Eyes are particularly vulnerable, and dust or mist is severely irritating to lungs and can cause ].<ref>{{Cite web |title=Hazardous Substance Fact Sheet: Potassium Hydroxide |url=https://nj.gov/health/eoh/rtkweb/documents/fs/1571.pdf |access-date=7 October 2024 |website=New Jersey Department of Health}}</ref> Safety considerations are similar to ].

The caustic effects arise from being highly alkaline, but if potassium hydroxide is ] with a non-toxic acid then it becomes a non-toxic potassium salt. It is approved as a food additive under the code E525.
]]]

==See also==
* ]
* ]
* ] – sailors' soap

==References==
{{reflist|30em}}

==External links==
{{Commons category}}
*
*
*

{{Potassium compounds}}
{{Hydroxides}}

{{Authority control}}

{{DEFAULTSORT:Potassium Hydroxide}}
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